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Electronics
VACUUM Classified A b s t r a c t s
IV
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Special
Subsidiary S u b j e c t s
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IV
Contd.
of f r a g m e n t s of processed material situated near the opening of the bottle. W h e n air is a d m i t t e d rapidly to the v a c u u m c h a m b e r containing bottles w i t h the closures of the new design the i n r u s h of air will excercise an additional .~orce on the closure such t h a t the k n o b s collapse a n d t h e closure is forced down o n t o the container flange sealing the bottle in t h e process. If t h e v a c u u m c h a m b e r is b r o u g h t u p gradually to atmospheric pressure no seal is m a d e and pressure in the bottle rises to atmospheric. A collar is t h e n placed over the closure a n d crimped u n d e r t h e flange of the container in order to effect a seal. A central hole in this cover facilitates the insertion of an h y p o d e r m i c needle for w i t h d r a w a l of the material w h e n required. F o r normal storage p u r p o s e s the hole is covered u p b y a second cap which in t u r n is held down b y an outer collar, the lower portion of which is crimped u n d e r t h e flange of t h e container. Sommaire: Ce b r e v e t ddcrit u n container de lyophilisation amdliord dans lequel le p r o d u i t est lyophilisd, et stockd aseptiqueraent.
45 - -
ELECTRONICS
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Ab~tr~t No. and Refereno~
A. D. Holmes & Armour & Co. Brit. Pa~
730,148
45
3211V
High Energy Physics See A b s t r a c t No.: 88/I
Production of Enriched Non-Radioactive Isotopes at Oak Ridge National Laboratory
33/1V
See A b s t r a c t No.: 74/II 34/IV
High Energy Particle Accelerators United Kingdom. The first particle accelerators gave o u t p u t s of a few h u n d r e d keV, b u t m o d e r n machines will soon operate at u p to 20-30 GeV. The lower energy a p p a r a t u s , however, is not obsolete. The article discusses the characteristics of the high-energy machines and the uses to which t h e y m a y be put. All accelerators of highenergy particles use acceleration b y an r.f. field across gaps, except the betatron, which accelerates electrons and uses the electric field associated w i t h a changing magnetic field. Particle stability is the m a i n problem. Firstly, the particles and fields m u s t be as near in phase a t the gaps as possible, and secondly, focusing m u s t be employed to p r e v e n t dissipation of a large n u m b e r of particles. I n linear accelerators a large n u m b e r of gaps in a s t r a i g h t line are used, while the o t h e r t y p e s of machine use a magnetic field to e m p l o y the same gap or gaps repeatedly. The linear accelerator is likely to be the b e t t e r machine for electrons, while the closed orbit machines are p r o b a b l y the best for heavier particles. The synchro-cyclotron is restricted b y the fact t h a t its cost rises rapidly as the energy r e q u i r e m e n t s increase owing to the large m a g n e t required. The p r o t o n s y n c h r o t r o n uses a fixed orbit radius and therefore only an a n n u l a r magnetic field is required, t h u s lowering the cost. The linear accelerator has reached 600 MeV (electrons) using a sectioned corrugated waveguide 60 m. long. Synchro-cyclotrons h a v e delivered p r o t o n s w i t h energies up to 450 MeV. Electron s y n c h r o t r o n s will operate at 5-6 GeV, and the p r o t o n machine a t a b o u t the same level, the orbit radius being a b o u t 18 m. These high energy machines are used for a v a r i e t y of nuclear experiments, of which polarisation effects in the scattering of p r o t o n s b y nuclei, and observation of individual particles of the meson group, are typical examples. Sommaire: Une revue des accdldrateurs de particule, ~ h a u t e dnergie actuellement employds, et t y p e d'expdriences faites avec ces appareils.
Berkeley Proton Linear Accelerator
Article by J. Coekcroft &
T. O. Pickavance Endeavour x4, April 1955 61-70
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United States. I n the historical introduction to their p a p e r the a u t h o r s p o i n t o u t t h a t a l t h o u g h the p r o t o n linear accelerator has n o w been bettered from the cost point of view b y the p r o t o n s y n c h r o t r o n it still h a s a n u m b e r of a d v a n t a g e s over the s y n c h r o t r o n , principally in the characteristics of the external beam. 85% of the b e a m is concentrated within a 3 ram. diam. circle; the angular divergence of the b e a m is 10 "s radian; the energy h o m o g e n e i t y is a b o u t 3 x 10-a; t h e average external b e a m c u r r e n t is a b o u t l0 s times t h a t of the 184-inch cyclotron and the average external b e a m c u r r e n t density is a b o u t 106 times as great. The general design characteristics are discussed with relation to cost, efficiency and safety. The wavelength was chosen to be 150 cm. because r a d a r e q u i p m e n t was available in this range. The p o w e r per unit-length is limited by x - r a y emission and electrical breakdown. I t is observed t h a t layers of p u m p oil are responsible for m o s t of the electron emission. The injection energy was chosen as 4 MeV, this being a reasonable voltage to attain with an electrostatic generat o r and also a high injection energy was desirable to accomplish focusing b y thin beryllium foils. The accelerator consists of 47 individual cavity resonators which h a v e to be individually t u n e d to the same r e s o n a n t frequency. Drift t u b e s are incorporated to shield the p r o t o n s while the field is in the w r o n g direction. A particle takes one full r.f. period to travel between mid-points of successive drift tubes. The a u t h o r s give m a t h e m a t i c a l t r e a t m e n t s for the voltage gain, p o w e r input, Q, and modes of the cavities. The general b e a m d y n a m i c s are considered mathematically. W h e t h e r or not a particle injected into the machine is accelerated t h r o u g h the machine depends on the p h a s e and velocity t h a t it has as the entrance to the machine. A set of curves is given from which the phase acceptance of the particle can be determined. The r e s o n a n t cavity of the accelerator is housed in a steel t a n k 40 ft. long and 48 inch. in diam. The top is hinged, 4 inch. above centre, and can be raised b y a pair of hydraulic cylinders. The v a c u u m gasket used in sealing, r u n s completely r o u n d the t a n k and is 90 ft. long.
October, 1955
Vacuum l'ol. I"
321
VACUUM Classified A b s t r a c t s
Abstract No. and References
Article by L. W. Alvarez, H. Bradner, J. V. Franck, :H. Gordon, J. D. Gow, L. C. Marshall, F. Oppenheimer, W. K. It. Panofsky, C. Riehman & J. R. Woodyard Rev. ~ci. Instrum.
26, Feb. 1955 111-133
36/iv
322
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The gasket is of flat-H cross section of moulded r u b b e r and is held to the un-machined flange b y special screws and retained by a ¼-inch square strip of steel, tack-welded to the v a c u u m side of the flange. The t a n k is m o u n t e d on a roller at one end to allow expansion and is prevented from rolling over b y the p u m p manifold which is resting on the floor. The r e s o n a n t cavity is a 'liner' m o u n t e d within the tank. I t is of dodecagon cross section, each face being a long copper strip the length of the liner, s u p p o r t e d on die-formed circumferential frames, in t u r n s u p p o r t e d b y spring s u p p o r t s to the main tank. The liner is also m o u n t e d to allow for expansion. The liner h a s 40 p u m p - o u t slots, 12 inch. long b y ½ inch wide. E a c h liner panel is cooled b y a 40 ft. length of t u b i n g t h r o u g h which w a t e r is circulated. The principle radiations from the accelerator were x - r a y s and fast neutrons. The x - r a y s were reduced to a safe level b y 1½ inch. of lead and the n e u t r o n s b y an 18 inch. thick wall of basalite concrete. X-radiation generally increased after opening the s y s t e m to air. After several m o n t h s r u n n i n g the s y s t e m had to be cleaned of p u m p oil deposits. The v a c u u m r e q u i r e m e n t s are m e t b y a 30-inch. three-stage diffusion p u m p and an 8-inch two-stage diffusion p u m p in series backed b y two 43 c.f.m. K i n n e y r o t a r y p u m p s in parallel. A refrigerated baffling s y s t e m was used. The p u m p i n g speed m e a s u r e d inside t h e liner was 2,500 1./sec. Many different types of v a c u u m seals are used in the s y s t e m including Teflon compression seals in the transmission line input. The machine operates with a total end-to-end voltage of 36 MV. The d u t y cycle is 0.9, the average power is a p p r o x i m a t e l y 20 kW. The oscillator s y s t e m consists of three pre-exciter oscillators and nine single-tube power oscillators, each connected to the liner t h r o u g h a separate transmission line and coupling loop. The correct mode of operation is chosen b y m a n u a l t u n i n g of the pre-exciter oscillators. The magnitude of the load impedance is adjusted b y v a r y i n g the size of the coupling loop in the liner. The power s y s t e m uses a s t a n d a r d three-phase m e r c u r y v a p o u r rectifier circuit charging a pulse-forming n e t w o r k t h r o u g h a reactance. The n e t w o r k is discharged into the load b y a triggered spark gap t h r o u g h a pulse transformer. A separate power s y s t e m feeds the pre-exciter oscillators. The pulse generator supplies a trigger pulse to the Van de Graaff generator which keys the ion source after the cavity is built up. One small m a g n e t deflects electrons formed in the final drift tubes u p w a r d s into a carbon catcher and a larger electro-magnet is used for separating the b e a m h a r m o n i c s and deflecting the b e a m to its desired position. The m e a s u r e d energy available is close to 31.7 MeV. Beam c u r r e n t available is ¼ tLA average, the m a x i m u m recorded being 0.37 ~zA at a recurrence rate of 15 c./sec. S o m m a i r e : Ddtails d ' u n accdl6rateur lin~aire de p r o t o n s opdrant m a i n t e n a n t 5. Berkeley; cet appareil a u g m e n t e l'dnergie des p r o t o n s jusqu'& une 6nergie finale de 31.5 MeV, p a r t a n t d ' u n 6jecteur Van de Graaff de 4 MeV.
Stanford High-Energy Linear Electron Accelerator (Mark III) United States. The Stanford electron accelerator Mark I I I is a travelling-wave accelerator employing 21 klystron amplifiers, feeding separate 10 ft. sections with 10-20 MW of pulsed power of a wavelength of 10.5 cm. The electrons are injected at 50-80 kV and travel 220 ft. in an a p e r t u r e of 2 cm. diam. E x p e r i m e n t a l stations are provided at points 10 ft., 100 ft. and 125 ft., along the accelerator as well as at three positions a t the end. A simple explanation of the principle of operation of a travelling-wave accelerator is given and it is pointed o u t t h a t the electron after the first few inches reaches nearly the velocity of light and thereafter the gain in energy of the electron is shown by a gain in mass. At the design values of 1=220 ft. and V = I , 0 0 0 MeV the electron 'sees' the accelerator as being 26 cm. long whereas the a p e r t u r e r e m a i n s relativistically unaltered. The acceler a t o r s t r u c t u r e is of the disc-loaded t y p e and the choice of the various design p a r a m e t e r s is discussed with a view to as high an o u t p u t as possible. These factors include materials, configuration, disc spacing, disc thickness, power distribution and frequency. The filling time for the s t r u c t u r e is chosen as 1 ~ sec. leaving 1 ~t sec. as the accelerating time when using 2 ~ sec. pulses. Special klystron amplifiers were developed which are synchronised b y supplying t h e m from a c o m m o n source. A single master-oscillator provides the necessary trigger pulses to operate the various pulsed components. A phase-shifter in the i n p u t to each klystron is adjusted to maximise the b e a m o u t p u t . The e a r t h ' s magnetic field is minimised b y w r a p p i n g the accelerator with hypersil and also b y degaussing coils. E a c h accelerator section is made up from five 2-ft. subsections made b y shrinking 23 copper discs in a prepared copper tube. The fabrication of the accelerator subsections is described in detail laying stress on the importance of attaining great accuracy and repeatability. A micro-wave m e a s u r i n g technique is used to check the internal diameter of the t u b i n g after machining and honing. I n the shrinking operation the tube is placed in a s t e a m jacket; the discs, m o u n t e d on an inner mandrel, are immersed in liquid nitrogen and t h e n the two are fitted together and allowed to reach r o o m temperature. The mandrel is r e m o v e d and the flanges at either end of the t u b e are machined to provide an O-ring slot which can be p u m p e d t h r o u g h a small hole to provide a g u a r d - v a c u u m space between the lapped ends of the section and the O-ring. The completed section is t h e n s u b m i t t e d to r.f. tests for m e a s u r e m e n t of phase velocity, group velocity, Q, impedance and reflections, m a t c h i n g of couplers and m e a s u r e m e n t s of imperfections. The klystrons are continuously p u m p e d to a pressure of a p p r o x i m a t e l y 10 -5 mm. Hg, when the cathode is hot. The accelerator v a c u u m is governed b y two factors, electrical b r e a k d o w n and electron scattering, and is a p p r o x i m a t e l y 2 x 10 "4 mm. H g when the accelerator is r u n n i n g at full power. The klystrons were specially developed for the application. The design is such t h a t the valve is d e m o u n t a b l e for replacement of the cathode b u t a sealed-off design is t h o u g h t to be feasible. The accelerator is fed by 21 klystrons, the p o w e r to each one of which is synchronised allowing for the time of flight of electrons t h r o u g h the accelerator. Power is transferred from the klystrons to the accelerator t h r o u g h an evacuated (10 -5 ram. Hg) waveguide. The klystrons are separated from the amplifier b y ceramic w i n d o w s brazed into the waveguide. Each 10 ft. section of accelerator is p u m p e d by a small oil diffusion p u m p t h r o u g h the i n p u t waveguide with a liquid nitrogen t r a p and a water-cooled baffle between p u m p and waveguide. Continuous monitoring of pressure is accomplished b y using ionisation gauges which are also used to give a l a r m in case of v a c u u m failure. Isolation valves of a special design are used to isolate 10 ft. sections for serviceing purposes. The g u a r d - v a c u u m between O-rings and lapped surfaces at the end of each accelerator section is obtained using a mechanical p u m p . The problem of injecting the electrons into the accelerator is discussed
Vacuum Vol. V
October, 1985
VACUUM Classified A b s t r a c t s
IV --
Special
Subsidiary
Subjects
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IV
Abstract No. and Referencea
Contd.
m a t h e m a t i c a l l y a n d d e s c r i p t i o n s a r e g i v e n of t h r e e t y p e s of g u n a n d p u l s i n g circuits w h i c h were tried. T h e g u n c u r r e n t l y in u s e is of t h e directly h e a t e d t u n g s t e n spiral t y p e d e v e l o p e d a t T e l e c o m m u n i c a t i o n s R e s e a r c h E s t a b l i s h m e n t , E n g l a n d . A t h e o r e t i c a l s t u d y of b u n c h e r s a n d b u n c h e r design is given. F a c t o r s c a u s i n g t r a n s v e r s e m o t i o n of t h e electron b e a m w i t h i n t h e accelerator are considered. A p a r t f r o m t h r e e i n t e r m e d i a t e t a p p i n g p o i n t s t h e m a i n b e a m is deflected b y m a g n e t s a t t h e e x i t of t h e accelerator to give electron b e a m s s u b s t a n t i a l l y free f r o m x - r a y s a n d n e u t r o n s b y either t h e ' a c h r o m a t i c p r i s m ' s y s t e m or t h e ' a c h r o m a t i c t r a n s l a t i o n ' s y s t e m . R a d i a t i o n shielding p r o b l e m s f r o m s u c h a h i g h e n e r g y accelerator are serious a n d are discussed fully. T h e principle sources of r a d i a t i o n h a z a r d are x - r a y s a n d n e u t r o n s . Discussion of n e u t r o n e n e r g y d i c t a t e s t h a t 5 ft. of concrete is n e c e s s a r y to r e d u c e t h e level to safe limits. A g r a d e d shield of concrete is u s e d for p r o t e c t i o n f r o m x - r a y s , ~,-rays a n d electrons, b e i n g 2 ft. t h i c k of o r d i n a r y concrete a t t h e i n p u t e n d a n d 3 ft. t h i c k of ferrite-loaded concrete a t t h e o u t p u t end. T h e m a x i m u m e n e r g y a t t h e t i m e of w r i t i n g w a s 630 MeV, t h e m a x i m u m a v e r a g e c u r r e n t is 1.0 I~A, m a x i m u m p e a k c u r r e n t is a b o u t 50 m A , t h e cross section of t h e b e a m is ¼ i n c h d i a m . a n d t h e b u l k of t h e e n e r g y is in a 2 % e n e r g y b a n d . T h e c u r r e n t available a t i n t e r m e d i a t e p o i n t s is h i g h e r t h a n a t t h e end. Sommaire: D6tails s u r u n acc616rateur lin6aire d'61ectrons, ~ h a u t e Snergie (Mark III) install6 h l ' U n i v e r s i t ~ de S t a n f o r d , ainsi q u e de s o n & t u i p e m e n t d'acc616ration, de t r a n s m i s s i o n de p u i s s a n c e radio-fr6quence, appareil auxilliaire, d y n a m i q u e s d u faisceau e t c e r t a i n s r 6 s u l t a t s s u r son f o n c t i o n n e m e n t .
Article by M. Chodorow, E, L. Ginzton, W. W. Hansen, R. L. Kyhl, R. B. Neal, W. K. H. Panofsky e2al. Rev. Sci. I ~ . a6z Feb. 1955 134-204
A Linear Accelerator for X - R a y Therapy See A b s t r a c t No.: 22/I
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Developments in Apparatus for Deep X - R a y Therapy See A b s t r a c t No.: 149/I
3s/Iv.
Medical Research Council's Cyclotron United Kingdom. T h e M.R.C. c y c l o t r o n a t H a m m e r s m i t h H o s p i t a l is to p r o d u c e b o t h n e u t r o n a n d c h a r g e d particle r a d i a t i o n , a n d radio-isotopes for t h e r a p y a n d research. T h e c y c l o t r o n is a 45-inch m a c h i n e , t h e m a g n e t core c o n s i s t i n g of e i g h t pieces. R e c t a n g u l a r a l u m i n i u m t u b i n g is u s e d for t h e c o n s t r u c t i o n of t h e coils (408 t u r n s each), a n d cooling is b y distilled w a t e r t h r o u g h t h i s t u b i n g . A s e p a r a t e h e a t e x c h a n g e r u s i n g t a p w a t e r cools t h e distilled w a t e r , t h e t a p w a t e r c i r c u l a t i n g t h r o u g h e v a p o r a t o r cooling towers. A field s t r e n g t h of 17 k g a u s s is o b t a i n e d across a n effective g a p of 8 inch. T h e lids of t h e v a c u u m b o x f o r m t h e pole faces ( ' A r m c o ' iron, 3 inch. thick, copper p l a t e d on t h e inside face). T h e v a c u u m b o x itself is of rolled brass, b r a z e d t o g e t h e r . T h e ' d e e ' s y s t e m is c o n v e n t i o n a l , a n d o p e r a t e s a t 11,286 Mc./sec. T h e m e a s u r e d Q is 4,550. T h e ion source is of the h o o d e d t y p e a n d h a s a vertical h a i r p i n f i l a m e n t fed f r o m a 500A 6V generator. T h e p u m p i n g a g g r e g a t e c o n s i s t s of t w o 16-inch diffusion p u m p s b a c k e d b y t w o m e c h a n i c a l p u m p s of 200 c u . f t . / m i n , c a p a c i t y . W i t h r e f r i g e r a t e d baffles t h e speed is 4,000 1./see. a t 10 "5 m m , H g for a v o l u m e of 4,000 1. Distilled w a t e r cooling is e m p l o y e d , a n d 5 / 10 "s ram. H g c a n be r e a c h e d in 2 hr, a n d 5 x 10 "6 ram. H g in 2 d a y s . T h e leak r a t e h a s b e e n m e a s u r e d a t 6 m i c r o n s p e r h o u r . T h e r.f. s y s t e m c o n s i s t s of a 12 k W t r a n s m i t t e r d r i v i n g t w o n e u t r a l i s e d B W 165 v a l v e s of 22.5 k W a n o d e dissipation. T h e o u t p u t a t t h e f r e q u e n c y s t a t e d is 75 k W . T h e m a c h i n e will give a 30 MeV ~-particle b e a m , a n d b e a m c u r r e n t s of 750 ~A of singly c h a r g e d h y d r o g e n m o l e c u l a r ions h a v e b e e n m e a s u r e d a t 6 i n c h radius. Sommaire: D e s c r i p t i o n d ' u n c y c l o t r o n install6 ~ l ' H S p i t a l d ' H a m m e r s m i t h p o u r la p r o d u c t i o n de n e u t r o n s , ou de r a d i a t i o n charg6es de p a r t i c u l e s et d ' i s o t o p e s radio-actifs.
39/Iv
Article by ~Luon. E~n~ x99, 17.6.1955 846-847
The x56-inch. Cyclotron at Liverpool United Kingdom. T h e e s s e n t i a l f e a t u r e s a n d u s e of t h e 156-inch. s y n c h r o - c y c l o t r o n a t Liverpool U n i v e r s i t y a r e described. T h e b u i l d i n g of t h e m a c h i n e w a s i n s t i g a t e d b y Sir J a m e s C h a d w i c k a n d its c o n s t r u c t i o n w a s c o m pleted in t i m e for t h e r e g u l a r e x p e r i m e n t al p r o g r a m m e c o n c e r n e d w i t h t h e p r o p e r t i e s of f a s t p r o t o n s , n e u t r o n s a n d pious, to begin in J a n u a r y , 1955. T h e b u i l d i n g h o u s i n g t h e m a c h i n e consists of t h e t w o - s t o r e y c y c l o t r o n r o o m w i t h a large a n t e - r o o m u s e d for e x p e r i m e n t a l w o r k . A b o v e t h e s e are s i t u a t e d v e n t i l a t i o n a n d cooling e q u i p m e n t . T h e c y c l o t r o n r o o m is h e a v i l y screened b y t h i c k concrete walls a n d s a n d s t o n e p a c k i n g , w i t h c h a n nels p r o v i d e d t h r o u g h t h e 12 ft. t h i c k concrete wall to allow b e a m s of particles to e n t e r t h e a n t e - r o o m . T h e m a g n e t h a s poles of 13 ft. d i a m . T h i s d i a m e t e r w a s d e t e r m i n e d b y t h e p l a n t a v a i l a b l e in B r i t a i n for t h e m a c h i n ing. T h e energising coils for t h e m a g n e t are cooled w i t h w a t e r c i r c u l a t i n g in t h e c o n d u c t o r , a n d p r o d u c e a c e n t r e field of 18,900 g a u s s c o r r e s p o n d i n g to a p r o t o n e n e r g y of 410 MeV. T h e g a p is 15.5 inch. n e a r t h e c e n t r e a n d ] 1.5 inch. a t t h e edge. T h e r.f. s y s t e m is similar to t h e t h r e e - q u a r t e r w a v e s y s t e m u s e d b y M a c K e n z i e (Berkeley) w h e r e t h e dee is coupled t h r o u g h a section of t r a n s m i s s i o n line to a v a r i a b l e c a p a c i t y , t h e o t h e r side of w h i c h is c o n n e c t e d t h r o u g h a s t u b line to earth. T h e dee is s u s p e n d e d in t h e v a c u u m t a n k . T h e t o t a l v o l u m e to be e v a c u a t e d is 30,000 1. a n d t h e p r e s s u r e c a n be r e d u c e d to 3 x 10 -6 ram. H g b y t w o 80-cm. m u l t i - s t a g e oil diffusion p u m p s w i t h a c o m b i n e d speed of 24,000 L/see. a t 10 -4 ram. Hg. As in-leakage of h y d r o g e n is necessary, t h e o p e r a t i n g p r e s s u r e is higher, i.e. 5 x 10 "5 ram. H g . T h e m e a n b e a m c u r r e n t is over 1 ~tA f r o m w h i c h a n ext r a c t e d b e a m of p r o t o n s of 383 MeV a n d a c u r r e n t of 3 × 10 "t I~A is available in t h e e x p e r i m e n t a l room. N e u t r o n s of energies 200-400 MeV are available, a n d b e a m s of pious of 150 M e V a n d 96 MeV m a y be e x t r a c t e d f r o m t h e tank. Sommaire: D e s c r i p t i o n des p a r t i e s essentielles et de r e m p l o i d ' u n s y n c h r o - c y c l o t r o n de 156 inches install~ ~t l ' U n i v e r s i t ~ de Liverpool.
40/IV
Article by M. J. Moore 2Vature x75 , 11.0.1955 1012-1015 •
October. 1955
V~cuum Vol. V
a
323
VACUUM Classified A b s t r a c t s Abstract No.
and References
41/IV
Note b y K. E. A. Effat & J. H. Fremlin J. Be/. I marum. 32, Sept. 19{~5 363-364
--
Special Subsidiary Subjects - Contd.
IV
A Circulation-System for He-3 United Kingdom. Reference is m a d e to e x p e r i m e n t s occasionally carried o u t in t h e B i r m i n g h a m 60-inch cyclotron e m p l o y i n g ions of helium-3. H e l i u m - 3 occurs in t h e a t m o s p h e r e as one p a r t p e r million a n d t e n t i m e s less in well-helium. H e l i u m , enriched w i t h t h e isotope of m a s s 3 to 2~/o, c a n be o b t a i n e d b u t is expensive. F o r t h a t reason a s y s t e m h a s been devised for t h e h e l i u m e m p l o y e d in e x p e r i m e n t s to be collected from t h e cyclotron, purified a n d recirculated to t h e i n s t r u m e n t . T h e s y s t e m m a k e s use of t h e fact t h a t charcoal cooled to liquid air t e m p e r a t u r e a b s o r b s all gases b u t h e l i u m . I n detail, t h e all-metal s y s t e m consists of a m e c h a n i c a l r o t a r y p u m p (disconnected while t h e h e l i u m is circulated), a n d t w o 14-inch off diffusion p u m p s o p e r a t i n g in parallel to e v a c u a t e t h e c y c l o t r o n v a c u u m c h a m b e r , b a c k e d b y a 1-inch m e r c u r y diffusion p u m p . A liquid air t r a p in f r o n t of t h e m e r c u r y diffusion p u m p r e m o v e s w a t e r a n d oil v a p o u r f r o m t h e s y s t e m . T h e m e r c u r y diffusion p u m p ejects t h e circulating g a s into t h e charcoal t r a p w h i c h consists of a s t a i n l e s s steel U - t u b e c o n t a i n i n g 35 g. of a c t i v a t e d charcoal cooled b y liquid air. A second m e r c u r y diffusion p u m p m a i n t a i n s a p r e s s u r e g r a d i e n t across t h e charcoal a n d r e t u r n s t h e purified h e l i u m t h r o u g h a needle v a l v e to t h e c y c l o t r o n source. W i t h t h e n o r m a l air leak (1-2 c.c./min, a t a t m o s p h e r i c pressure) t h e c i r c u l a t i n g o p e r a t i o n c a n be m a i n t a i n e d for 8 hr. w i t h o u t u n d u e rise of t h e n o r m a l o p e r a t i o n a l p r e s s u r e w h i c h is 3 × 10 -6 m m . H g . On c o m p l e t i o n of a r u n t h e g a s e s a b sorbed in t h e charcoal t r a p , w h i c h s h o u l d a m o u n t to a b o u t ½ 1. of air a t a t m o s p h e r i c pressure, are r e m o v e d b y h e a t i n g t h e t r a p to 400°C. T h e g a s e s liberated are w i t h d r a w n b y m e a n s of a n a u x i l i a r y p u m p . Sommaire: Description d ' u n s y s t ~ m e p o u r rc~cup~rer et recirculer l'h61ium; ce s y s t ~ m e est employ~ p o u r c e r t a i n s t r a v a u x avec le cyclotron de 60 inches de B i r m i n g h a m .
42]IV
Radioisotope Production Rates in a zz-MeV Cyclotron See A b s t r a c t No.: 142/III
43/IV
S o m e Properties of a Simple O m e g a t r o n - T y p e M a s s Spectrometer See A b s t r a c t No.: 4 7 / I I
44/IV
Theory and Probe Measurements in a Magnetic Ion Source Belgium. A m a g n e t i c ion source is described consisting of a cylindrical t u b e (the anode) p a r t i a l l y closed a t each e n d b y a disc p e r f o r a t e d a t t h e centre. E a c h of t h e s e holes o p e n s into a s h o r t cylindrical c h a m b e r of t h e s a m e d i a m e t e r as t h e anode; in one c h a m b e r is t h e f i l a m e n t w h i c h serves as t h e source of electrons, in t h e o t h e r a F a r a d a y cylinder for t h e e x t r a c t i o n of ions a n d a p a s s a g e to t h e p u m p i n g s y s t e m . H a l f - w a y a l o n g t h e a n o d e is a side t u b e c o n t a i n i n g a L a n g m u i r p r o b e carried b y a s p r i n g - r e t a i n e d iron piston. B y m e a n s of a m a g n e t , t h e probe c a n be m a d e to p r o t r u d e into t h e a n o d e t u b e to i n v e s t i g a t e t h e potential, etc., a t v a r i o u s p o i n t s a l o n g t h e d i a m e t e r of t h e anode. B o t h e n d - p l a t e s a n d c h a m b e r s are e a r t h e d , while t h e a n o d e is c o n n e c t e d t h r o u g h a resistor a n d a c u r r e n t m e t e r to a positive poten*,_'al. T h e probe c a n be m a d e either positive or negative, a n d h a s its o w n v o l t m e t e r a n d a m m e t e r . T h e whole t u b e fits inside a pair of H e l m h o l t z coils w h i c h p r o d u c e a n axial m a g n e t i c field. T h e f i l a m e n t a n d one e n d - p l a t e a c t as t b e c a t h o d e a n d e m i t e l e c t r o n s a l o n g t h e axis of t h e anode; t h e electrons oscillate in t h e c o m b i n e d electric a n d m a g n e t i c fields a n d c a u s e ionisation of t h e g a s filling. A t h e o r y is o u t l i n e d l e a d i n g to e q u a t i o n s for t h e densities of electrons a n d ions as f u n c t i o n s ~f d i s t a n c e from t h e axis, in t h e ' n o r m a l s t a t e ' (ionic d e n s i t y neglected) a n d in t h e ' s u p e r s t a t e ' (ionic a n d electronic densities r o u g h l y equal). P r o b e c h a r a c t e r i s t i c s were i n v e s t i g a t e d e x p e r i m e n t a l l y for t h e s u p e r s t a t e ; w i t h a cylindrical probe t h e ionic b r a n c h of t h e characteristic w a s f o u n d to be similar to t h a t for o r d i n a r y discharges, w i t h t h e s q u a r e of t h e c u r r e n t falling linearly w i t h increasing positive p o t e n t i a l . T h e r e s u l t s of t h e e x p e r i m e n t s , perf o r m e d w i t h m e r c u r y v a p o u r , were f o u n d to agree w i t h t h e theoretical prediction of ionic or electronic d e n s i t y as a G a u s s i a n f u n c t i o n of d i s t a n c e f r o m t h e axis. B y c o m p a r i n g t h e radial d i s t r i b u t i o n of t h e space p o t e n t i a l w i t h t h e a c t u a l a n o d e potential, t h e q u a n t i t y k T + / q w a s e v a l u a t e d , a n d h e n c e T + , t h e ionic t e m p e r a t u r e ( k = B o l t z m a n n ' s C o n s t a n t , q = i o n i c charge). V a l u e s of T + as h i g h as 720,000°K h a v e been found. T h e electronic b r a n c h of t h e c h a r a c t e r i s t i c w a s f o u n d difficult to i n t e r p r e t . Sommaire: O n a ~tudi~ e x p 6 r i m e n t a l e m e n t et t h $ o r i q u e m e n t le ' s u p e r s t a t e ' d u n s u n e source m a g n ~ t i q u e d'ion.
Article by M. Hoyaux, R. Lema;tre & P. Gsns
J. Ap'pl. Phya. a6, Jan. 1955 110-112
$24
IV
45/iv
Plutonium: Evaporation Tests, Ionisation Potential and Electron Emission See A b s t r a c t No.: 112/I
46/iv
Uniform Field Breakdown" in A i r See A b s t r a c t No.: 63/1
47/iv
Electrical B r e a k d o w n a t V e r y L o w G a s Pressures See A b s t r a c t No.: 62/I
Vacuum Vol. V
October, 1966
VACUUM Classified Abstracts
IV
-
-
Special Subsidiary Subjects --
IV
Contd.
Artificial Increase of Electrical Breakdown S t r e n ~ h of Air at Low Pressure in the R e . o n of 300 Mc./s. United Kingdom. Experiments carried out in the past applying high frequency energy to an electrode system separated by a small air gap at low pressures (59 ram. Hg and upwards) proved t h a t the use of a d.c. bias voltage can delay the electrical breakdown. The authors report on fresh experiments extending the study to the pressure range 5-120 ram. Hg and using gap widths from 1-4 ram. Two frequencies were employed, 227 and 379 Mc./sec. The d.c. bias voltages ranged from 0-125V. Breakdown will be effected eventually if the life of the free electrons in the gap is longer t h a n half a period of the applied high frequency stress, thus facilitating the building up of an electron avalanche. Where these conditions exist, the presence of a d.c. bias voltage causes the withdrawal of free electrons, which may otherwise contribute to avalanche formation from the gap, by attracting t h e m to the anode. A graph is shown giving the results for a series of experiments carried out a t a pressure of 20 ram. Hg and a high frequency energy of 378.5 Mc./sec. The phenomenon described can be used in practice to inhibit breakdown in electronic equipment operating a t high altitudes. Sommaire: Le phdnombne par lequel un courant continn moddr6 s u p e r p o ~ sur une ultra haute fr~quence appliqu6e ~ un espace variant de 1 ~ 4 mm. sous pressions de l'ordre de 5 ~ 120 mm. Hg, augmente considdrablement la tension de claquage ~ haute fr&quence.
Role of Positive Ions in High-Voltage Breakdown in Vacuum United States. I t has been suggested t h a t one of the more important processes contributing to high voltage breakdown between metallic electrodes in vacuum is electron emission from the cathode due to positive ion bombardment. The results so far obtained cannot be properly correlated because of the varying experimental methods. The study reported in the present article was essentially concerned with three basic factors governing electron emission caused by positive ion bombardment: (a) The effect of high extractive cathode gradlants, (b) the effect of different metallic targets and (c) the effect of different positive ions. Details of the experimental set-up are given. An ion beam of 0.07 [~A, produced by electrons emitted from a ring-shaped tungsten filament on a cup shaped anode, were passed into the acceleration gap, hitting an electrode at earth potential. The latter consisted of a disc which could be rotated and in which were, alternatively, a ½-inch hole and three ½-inch insulated targets of different metals. If the hole w a s placed in the path of the ion beam the latter was collected in a Faraday cage positioned underneath the disc-shaped electrode. The cathode gradient and the total ion energy could be varied by adjusting the terminal voltage and the gap length. The pressure in the system was 6 X I0 "i mm. Hg and total gap voltages ranged from 10 to 140 kV. The experiments were conducted either in helium, hydrogen, nitrogen, xenon, or mercury. Targets of magnesium, aluminium, steel, copper, gold and lead were employed. In each case initial rapid rise of electron emission with ion energy was followed by a slowlinear increase. The emission from aluminium and magnesium target bombardment with helium ions varied slightly with cathode gradient but the emission of other targets such as lead and gold was independent of the value of the cathode gradient. Minimum electron emission was obtained for materials, the atomic number of which was about 40 and the density of which was in the ~eighbourhood of 9 g./c.c. The highest numbers of electrons produced by a positive ion was obtained in bombarding steel with nitrogen ions. By inclining the target to the electron beam the emission could be increased. For an angle of 30 ° between ion beam and target surface the emission was doubled. Previous workers have established t h a t the positive ion emission from metals bombarded by electrons is less t h a n one ion per 1,000 electrons (coefficient A). In this work, it was found t h a t less than twenty electrons are released per impinging positive ion (coefficient B). The particle-interchange theory of high-voltage breakdown in vacuum stipulates t h a t A × B > 1 to produce the required instability to initiate a chain reaction causing eventual vacuum breakdown. The present experiments proved t h a t the secondary electron emission was quantitatively inadequate to fulfil this condition. The present investigation however does not take into account the possible formation of negative ions. Also the outcome of the experiments does not exclude the possibility t h a t vacuum breakdown is caused b y larger atomic aggregates than simple gaseous ions and reference is made in this connection to Cranberg's 'clump' theory of vacuum breakdown (see Volume I I Abstract No. 60/IV. (See also Abstract No. 50/IV.) Sommaire: On a mesurd l'dmission dlectronique de cibles de magndsium, aluminium, cuivre pur, or et plomb, soumises ~ un bombardement d'ions de diff6rents gaz.
Composition of t h e Interelectrode Prebreakdown Current in High Vacuum United States. The study reported in the present article is connected with the work recorded in Abstract No. 49/IV and is concerned essentially with the composition of the interelectrode prebreakdown current. Details of the experimental set-up are given. Measurements were taken on a pair of aluminium electrodes and a pair of steel electrodes. One of the two electrodes was of low heat capacity and thermally insulated, and the other was of large heat capacity remaining a t substantially constant temperature throughout an experimental run. T h e gap between the two electrodes was ~ inch, the high voltage source was a Van de Graaff generator and the gap voltages used were 80-100 kV. The pressure was 5 × 10" ram. Hg. By measuring the rate at which the temperature of the heat insulated electrode rose, the relative amount of prebreakdown current carried b y negatively and positively charged particles passing through the gap could be ascertained. The experiments indicated t h a t the prebreakdown current was composed chiefly of negatively charged particles. In the case of the alumiuium electrode the electrons outnumbered the positive ions by more than 300:1, and in the case of the steel electrode the figure was 1,000:l. I t was established in previous studies t h a t about 1,000 electrons are required for t h e emission of one positive ion. In the work recorded in the previous abstract it was found t h a t no more t h a n twenty electrons were produced b y one impinging positive ion. I t appears t h a t the predominantly negative
October, 1955
Vacuum Vol. V
Ab~.~t No. and Referenoes
is/iv
Letter by G. W. E. Stark & G. L. Fougere Nature x74, 4.12.1964 1066
49/Iv
Artiole by H. C. Bourns, Jr., R. W. Cloud & J. G. Trump J. Appl. Phys. a6, May 1955 596-599
~o/Iv
325
VACUUM Classified A b s t r a c t s
Abstract No.
IV
and Referenees
Article by H. C. Bourne, Jr., J. A~pl. Phys. • 6, May 1955 625-626
5~/IV
Note by P. F. Browne PTo¢. Phys. 8oe. 68B, Aug. 1955 564-566
Special
Subsidiary Contd.
Subjects
m
IV
emission e s t a b l i s h e d in t h e p r e s e n t e x p e r i m e n t s m u s t be c a u s e d b y a d d i t i o n a l m e c h a n i s m s s u c h as field e m i s s i o n o p e r a t i v e in t h e c o n d i t i o n s s t a t e d . Sommaire: D e s m e s u r e s s u r l ' a u g m e n t a t i o n de t e m p e r a t u r e d ' u n e 61ectrode s o u m i s e ~ d e s t e n s i o n s de l'ordre de 80 ~ 100 k V m o n t r e q u e le c o u r a n t de pr~-claquage est compos6 p r i n c i p a l e m e n t de p a r t i c u l e s charg6es n 6 g a t i v e ment.
The Transfer of Metal Between Electrodes in a H i g h V a c u u m on Application of a H i g h Electric Field Eire. D e t a i l s are given of a series of e x p e r i m e n t s c o n d u c t e d for t h e p u r p o s e of c h e c k i n g C r a n b e r g ' s t h e o r y of t h e i n i t i a t i o n of h i g h v a c u u m electric b r e a k d o w n (see V o l u m e II A b s t r a c t No. 60/IV). T w o electrode s y s t e m s were u s e d : (a) W i r e a n o d e - - p l a n e c a t h o d e a n d (b) p l a n e a n o d e - - p l a n e cathode. T h e m a t e r i a l w a s nickel or lead a n d the a n o d e s were coated w i t h deposit of =-active p o l o n i u m of a d e n s i t y of 10 xl a t o m s p e r s q . c m . T h e t r a n s f e r of p o l o n i u m w a s recorded b y m e a n s of a n u c l e a r plate. T h e g a p e m p l o y e d w a s 1 ram. a n d d.c. v o l t a g e s u p to 80 k V were applied. C l u m p s f o r m e d on t h e c a t h o d e a t v o l t a g e s below a n d a b o v e t h e s p a r k i n g voltage. A t large g a p s occasional s p a r k s occurred w i t h o u t p r o d u c i n g c l u m p s . I t w a s f o u n d t h a t a h i g h field r a t h e r t h a n a h i g h v o l t a g e was c a u s i n g t h e i r a p p e a r a n c e . C u r r e n t s of 10"lSA for 1 m i n . resulted in c l u m p f o r m a t i o n . T h e area covered b y e a c h c l u m p w a s less t h a n 10 "~ sq.cm. T h e e x p e r i m e n t s i n d i c a t e d t h a t positive ions f o r m e d from t h e p o l o n i u m d e p o s i t on t h e a n o d e f o r m e d c l u m p s on t h e c a t h o d e on being d r a w n to p o i n t s of field emission. Conditions m o r e t y p i c a l of t h e C r a n b e r g c l u m p e x p l a n a t i o n were f o u n d in a special e x p e r i m e n t w h e r e t h e a n o d e consisted of a s h a r p e n e d t i p of a nickel wire 0.053 cm. d i a m , a n d a p l a n e c a t h o d e , t h e g a p b e i n g 0.025 cm. N i n e t e e n c l u m p s were f o u n d in a n a r e a of a b o u t 1 sq.cm, of t h e cathode. T h e effect of solid c l u m p s b e i n g d e t a c h e d f r o m t h e anode m a y be p r o d u c e d b y electrostatic forces. A calculation in t h e p a r t i c u l a r case i n d i c a t e d t h a t t h e electros t a t i c s t r e s s a t t h e a n o d e a t b r e a k d o w n agreed well w i t h t h e tensile s t r e n g t h of t h e electrode. I n a n o t h e r series of e x p e r i m e n t s t w o p l a n e electrodes were u s e d b u t t h e c a t h o d e w a s c o a t e d w i t h t h e p o l o n i u m deposit. I n t h i s e x p e r i m e n t , too, c l u m p f o r m a t i o n w a s observed. T h e r e w a s a series of s m a l l e r a n d a series of larger c l u m p s on t h e cathode, a n d in a d d i t i o n a n u m b e r of c l u m p s on t h e anode. I n t h i s case t h e c l u m p s c a n n o t h a v e been f o r m e d b y m a t e r i a l t r a n s f e r as o n l y t h e c a t h o d e w a s radioactive. I t is believed t h a t p o l o n i u m ions, f o r m e d b y positive ion b o m b a r d m e n t of t h e cathode, c o n c e n t r a t e in p o i n t s of field emission. T h i s will e x p l a i n w h y t h e r e are s m a l l and large c l u m p s on t h e r a d i o a c t i v e c a t h o d e . T h e c l u m p s o b s e r v e d on t h e n o n - r a d i o a c t i v e a n o d e m a y originate b y m a t e r i a l t r a n s f e r f r o m s u c h p o i n t s on t h e c a t h o d e s u r f a c e w h e r e electron emission, w h i c h c a u s e s t h e conceno t r a t i o n of p o l o n i u m ions in t h e f o r m of a m a j o r c l u m p , is i n t e n s e e n o u g h to m e l t or d i s r u p t t h e c a t h o d e surface. T h e r e s u l t s of t h e l a t t e r series of e x p e r i m e n t s i n t r o d u c e s a n e l e m e n t of d o u b t i~ato t h e t r u e origin of c l u m p s as conceived b y Cranberg. Sommaire: O n a ~tudi6 le t r a n s f e r t de m ~ t a l e n t r e ~lectrodes, sous vide pouss6.
52/iv
Work Function of Tungsten Single Crystal Planes Measured b y the Field Emissioh Microscope See A b s t r a c t No.: 60/II
53/xv
The Effect of Gases on the Contact Potentials of Evaporated Metal F i l m s United States. T h e effect w i t h t i m e of o x y g e n , nitrogen, w a t e r v a p o u r a n d air on t h e c o n t a c t p o t e n t i a l differences b e t w e e n aged b u l k p l a t i n u m a n d e v a p o r a t e d m e t a l films w a s s t u d i e d b y t h e v i b r a t i n g c o n d e n s e r m e t h o d . T h e m e t a l s u s e d were a l u m i n i u m , lead, nickel, c h r o m i u m a n d iron. B o t h reversible a n d irreversible effects were observed. A n e x p l a n a t i o n is offered b a s e d on s o r p t i o n of t h e g a s e s w h i c h p r o v i d e either a dipole barrier or a n ion barrier to t h e emission of electrons. (Authors) Sommaire: O n a 6tudi6 les effets d a n s le t e m p s , de l'oxyg~ne, azote, v a p e u r d ' e a u et air s u r les diff6renees de potentiel de c o n t a c t e n t r e p l a t i n e b r u t vieilli et films de m ~ t a l 6vapor6s.
Article by N. Haekerman & E. H. Lee J. Phys. Chem. 59, Sept. 1955 900-906
54/iv
326
--
A Demountable Vacuum System for Secondary Emission Studies See A b s t r a c t No.: 21]I
55/Iv
Improvements i.o.r.t. Vacuum Tight Joints See A b s t r a c t No.: 106/II
56/Iv
Ceramic-to-Metal Sealing See A b s t r a c t No.: 87/II
57/IV
Ceramic Twin-Triode Pumping Technique See A b s t r a c t No.: 23/II
Vacuum Vol. V
October, 1955
VACUUM Classified A b s t r a c t s
IV
Special Subsidiary Subjects --
IV
Contd.
The Vacuum Valve and Semiconductors France. A l t h o u g h s o m e of t h e r e l e v a n t p r o p e r t i e s of s e m i c o n d u c t o r s h a v e b e e n k n o w n for s o m e t i m e , it w a s t h e i n v e n t i o n of t h e t h e r m i o n i c triode v a l v e in 1913 w h i c h f o r m e d t h e f o u n d a t i o n s t o n e of electronics as we k n o w it t o d a y . H o w e v e r , t h e i n v e n t i o n of t h e t r a n s i s t o r in 1948 h a s a d d e d a n e w a n d i m p o r t a n t b r a n c h to electronic science. T h e p r e s e n t p a p e r p r e s e n t s a c o m p a r a t i v e e v a l u a t i o n of t h e t h e r m i o n i c v a l v e a n d t h e t r a n s i s t o r . I n t h e t h e r m i o n i c valve, e l e c t r o n s or ions are m o v i n g freely on a n e s s e n t i a l l y u n i m p e d e d p a t h . I n t h e t r a n s i s t o r t h e e l e c t r o n s a r e 'tied' to t h e m e d i u m in w h i c h p r o p a g a t i o n t a k e s place a n d t h i s m e d i u m exercises a n appreciable r e s i s t a n c e to a n y forces a p p l i e d e x t e r n a l l y . T r a n s p o r t of electricity in t h e t h e r m i o n i c v a l v e is e s s e n t i a l l y obt a i n e d a t t h e e x p e n s e of a p p l y i n g g r e a t e n e r g y in t h e f o r m of h e a t , t h e d i s s i p a t i o n of w h i c h o f t e n p r e s e n t s t r o u b l e s o m e p r o b l e m s . T r a n s p o r t of electricity in s e m i c o n d u c t o r s on t h e o t h e r h a n d is c o m p a r a t i v e l y simple; it t a k e s place a t r o o m t e m p e r a t u r e a n d is effected t h r o u g h t h e i n t e r m e d i a r y of a p - n j u n c t i o n . T h e speed of t h e m o t i o n of t h e free e l e c t r o n s in t h e t h e r m i o n i c v a l v e is large a n d b e c o m e s a l i m i t i n g factor o n l y a t frequencies of several h u n d r e d m e g a c y c l e s . Besides, t h e finite t i m e t a k e n b y t h e electrons for t h e i r p a s s a g e is a n a d v a n t a g e in c e r t a i n a p p l i c a t i o n s of specially d e s i g n e d t h e r m i o n i c valves. T h e p a s s a g e of electricity in a s e m i c o n d u c t o r , on t h e o t h e r h a n d , is b o u n d to be slow d u e to f r e q u e n t collisions w i t h t h e a t o m s of t h e m a t e r i a l . A f o r m u l a is given to define t h e speed of t h e p a s s a g e of electricity in s e m i c o n d u c t o r s s u c h as g e r m a n i u m . A n appreciable loss of g a i n is i n c u r r e d if e m p l o y e d a t f r e q u e n c i e s a b o v e 2 Mc./sec. T h e t r a n s i t t i m e is p r o p o r t i o n a l to t h e s q u a r e of t h e d i s t a n c e b e t w e e n e m i t t e r a n d collector a n d g r e a t t e c h n i c a l difficulties h a v e to be o v e r c o m e in o r d e r to r e d u c e t h i s d i s t a n c e to a v a l u e of t h e o r d e r of a few microns. A t t h a t distance, frequencies u p t o a few h u n d r e d m e g a c y c l e s m a y be e m p l o y e d b u t t h e r e is t h e c o n s t a n t d a n g e r of s h o r t circuiting collector a n d e m i t t e r . T h e effect of a n y p a r a s i t i c p h e n o m e n a w i t h i n a t h e r m i o n i c v a l v e c a n largely be c o m p e n s a t e d for, b u t in t h e case of t h e t r a n s i s t o r t h e whole m e c h a n i s m of o p e r a t i o n is n o t sufficiently explored to c o u n t e r a c t s u c h p h e n o m e n a b y a n y t h i n g b u t t e n t a t i v e m e a s u r e s . T h e p r o b l e m of noise is e q u a l l y u n s o l v e d . A l t h o u g h t h e r e is still m u c h w o r k to be carried o u t in o r d e r to m a k e t h e s e m i c o n d u c t o r a real rival to t h e t h e r m i o n i c v a l v e t h e fact s h o u l d n o t b e ignored t h a t t h e t r a n s i s t o r c a n be a p p l i e d w i t h a d v a n t a g e w h e r e a device of s m a l l d i m e n s i o n s a n d low c o n s u m p t i o n is required. Somma ire : L ' a u t e u r fait u n parall~le e n t r e le t u b e ~ vide et les s e m i - c o n d u c t e u r s , e x p o s a n t leurs a v a n t a g e s et l e u r s i n c o n v 6 n i e n t s respectifs.
Ab,tract No. and References
5s/iv
Article by J. Laplume Le V/de zo, March-April 1955 2-8
The Vacuum Obtainable in a Thermionic Valve and its Measurement See A b s t r a c t No.: 20/I
59/IV
Deterioration of Oxide Cathodes b y the Evolution of Gas from the Anode Under Electron Bombardment See A b s t r a c t No.: 19/I
6o/xv
Evaporation of Barium and Strontium from Oxide-Coated Cathodes United States. A n e x p e r i m e n t a l s t u d y is r e p o r t e d of t h e factors g o v e r n i n g t h e e v a p o r a t i o n , f r o m oxide c a t h o d e s , of b a r i u m , s t r o n t i u m a n d t h e i r c o m p o u n d s . T h e f a c t o r s s t u d i e d are: (1) O p e r a t i n g t e m p e r a t u r e , (2) s p a c e c u r r e n t d e n s i t y , (3) i m p u r i t i e s of t h e c a t h o d e core m a t e r i a l (nickel), (4) c o m p o s i t i o n of o t h e r electrodes. I n t h e m a i n series of e x p e r i m e n t s , a b o u t 400 triodes h a v i n g e s s e n t i a l l y t h e s t r u c t u r e of a r e p e a t e r v a l v e were a s s e m b l e d , p u m p e d a n d aged u n d e r identical conditions, b a t c h e s of 4 0 - 1 0 0 b e i n g s t u d i e d statistically. S a m p l e s of 3-15 v a l v e s were selected a t r a n d o m i m m e d i a t e l y a f t e r p u m p i n g , a n d a t i n t e r v a l s d u r i n g t h e ageing, for a n a l y s i s ; t h e grid a n d a n o d e were r e m o v e d f r o m e a c h valve, t h e m a t e r i a l collected on t h e m dissolved in h y d r o c h l o r i c acid a n d t h e s o l u t i o n s a n a l y s e d s p e c t r o c h e m i c a l l y b y t h e c o m p a r i s o n s t a n d a r d m e t h o d . T h e r e s u l t s g a v e t h e c u m u l a t i v e e v a p o r a t i o n w h i c h h a d occurred d u r i n g p u m p i n g a n d d u r i n g v a r i o u s periods of ageing, a n d were e x p r e s s e d in m i c r o g r a m p e r s q . c m , of c a t h o d e surface. T h e ageing c o n d i t i o n s were: F i l a m e n t t e m p e r a t u r e - - 1,02O°K, a n d a n o d e p o t e n t i a l - - 1 3 5 V g i v i n g a s p a c e c u r r e n t of 1 0 m A / c m . I. T h r e e t y p e s of nickel were u s e d as core m a t e r i a l for t h e filaments, t w o w i t h a b o u t 0 . 8 4 % i m p u r i t y , t h e t h i r d w i t h 0.03%. W i t h t h e l o w - p u r i t y s a m p l e s , a b o u t 50-80 ~g./sq.cm. w a s e v a p o r a t e d d u r i n g p u m p i n g , w h e n t h e f i l a m e n t w a s flashed a t 1,300°K for 2 m i n . T h e t o t a l increased to 110 ~g. a f t e r a b o u t 3,000 hr. ageing, followed b y a s t e a d y f u r t h e r increase of a b o u t 2 vg. p e r 1,000 hr. u p to 20,000 hr. (the l o n g e s t period quoted). T h e figures for t h e h i g h - p u r i t y nickel s h o w e d a b o u t 40 ~g. d u r i n g p u m p i n g a n d no significant increase d u r i n g ageing. I n all cases, s t r o n t i u m a c c o u n t e d for o n l y a b o u t 5 o of t h e t o t a l a n d it w a s concluded, from k n o w l e d g e of t h e v a p o u r p r e s s u r e s of B a O a n d SrO a t 1,300~K, t h a t v e r y little of either m e t a l could h a v e e v a p o r a t e d as oxide. T h i s conclusion, t h a t t h e p u r e m e t a l is involved, w a s c o n f i r m e d b y a second series of e x p e r i m e n t s in w h i c h t h e e v a p o r a t e d m a t e r i a l w a s cond e n s e d on a t u n g s t e n r i b b o n (the t e c h n i q u e of B e c k e r a n d Sears), t h e t h e r m i o n i c e m i s s i o n of w h i c h w a s t h e n o b s e r v e d , a n d b y o t h e r t e s t s in w h i c h t h e m a t e r i a l w a s allowed to r e a c t w i t h w a t e r v a p o u r , p r o d u c i n g h y d r o g e n . T e s t s w i t h o u t space c u r r e n t flow s h o w e d t h i s to h a v e a negligible effect on t h e e v a p o r a t i o n rate. T h e effect of f i l a m e n t t e m p e r a t u r e w a s t h a t a n increase of 80 ° to 1,100°K g a v e a four-fold increase in t h e t o t a l e v a p o r a t i o n of b a r i u m d u r i n g t h e first 4,000 hr. A factor n o t a t first s u s p e c t e d w a s t h e influence of a n o d e a n d grid m a t e r i a l (bright nickel in t h e first e x p e r i m e n t s ) . T h e u s e of cleaned a n d s u b s e q u e n t l y oxidised nickel a n o d e s a n d grids g r e a t l y r e d u c e d e v a p o r a t i o n , especially w i t h h i g h - p u r i t y nickel filaments, s u g g e s t i n g t h a t i m p u r i t i e s f r o m a n o d e and grid m a y h a v e c o n t r i b u t e d to t h e s u p p l y of excess b a r i u m in t h e c a t h o d e . I n fact, m a g n e s i u m w a s d e t e c t e d in t h e oxide c o a t i n g itself w h e n b r i g h t nickel a n o d e s were used, e v e n w i t h h i g h - p u r i t y nickel filaments. Cont r a r y to w h a t m i g h t h a v e b e e n e x p e c t e d , no correlation w a s f o u n d b e t w e e n t h e r m i o n i c e m i s s i o n a n d e v a p o r a t i o n . S o m m a i r e : L e s t a u x d ' ~ v a p o r a t i o n d u b a r i u m et d u s t r o n t i u m d u c a t h o d e s ~ o x y d e d ' u n t u b e c o u r a n t o n t 6t~ m e s u r 6 s p e n d a n t d e s essais d u dur~e jusqu'~. 20,000 h e u r e s .
01/IV
October, 1955
Vacuum Vol. V
Article by L. A. Wooten, A. E. Ruehle & G. E. l~oore J. AppL Phys. 26, Jan. 1955 44-51 327
VACUUM Classified Abstracts
Abstract No.
IV
and References
62/iv
Note by R. Levi J. Appl. Phys.
26, May 1955 639 & Le Vide
9, Nov. 1954 284-289 63/IV
--
Special
Subsidiary Contd.
Subjects
--
IV
Improved 'Impregnated C~thode' United States. Details are given of the properties of the new impregnated cathode which represents a development of the L-cathode. The same porous tungsten body of 3 ram, diameter as in the case of the L-cathode is used. The body is impregnated in a hydrogen atmosphere with a melt containing 5 moles of BaO, 2 moles of A l s o a and 3 moles of CaO. The L-cathode was impregnated in vacuum and the material consisted of 5 moles of BaO and 2 moles of A l t o s. The emission current density, measured pulsewise by discharging periodically across the diode an R-C network, having a time constant of 60 ~ see., at a repetition rate of 60 per see., has been increased four times. The ageing process required to obtain full and stable emission has been reduced from 3 days to 3 hr. The average total barium evaporation rate during the first 2,000 hr. of service life is reduced to 2 x l0 "~° g. of Ba per sq.cm, per sec. at 1,465°K. Life tests carried out at the same temperature exceeded 5,000 hr. without any failure. The operating characteristics of the new cathode when employed in a typical diode valve are shown in a graph. Sommaire: Des recherches faites auparavant dans le but d'am61iorer les techniques de fabrication de cathodes du type L ont cenduit au d~veloppement de 'cathodes impr6gn~es'.
The Evolution of Particle Counters Switzerland. Counting devices necessary for assaying the rate of emission of particles have become of general
Article by H. Oreinacher Endeavour
I3, Oct. 1954 190-197 64/IV
scientific importance. The evolution of counters is surveyed and the principle characteristics of types at present in use are reviewed. Elster and Geitel discovered in 1903 t h a t m-particles striking zinc blende (ZnS) produce light flashes. This device was employed for the detection and counting of "-particles until Rutherford and Geiger in 1908 developed an improved method for the detection and counting of "-particles by means of their ionising action. This led to the first design of the proportional (gas multiplication) counter. Details of the operating principle of the counter are given. The method ranges today among the fastest available: 1,000,000 a second can be counted. I t facilitates the counting of =-particles independently of any ~-particles since the latter have about 100 times weaker an ionising power. Geiger developed in 1913 t b e p o i n t counter. The output of this instrument is proportional to the primary ionisation and facilitates the counting of ~- ~- and 7-particles. An instrument which facilitated the measurement of the ionisation produced by single ,,-particles and protons was developed by Kohlrausch and Schweidler in 1912, known as the electrometer counter. However its counting is slqw and therefore the method is not generally applied. In 1924 the author of the present article developed the so-called chamber counter which facilitates the detection of particles directly through their primary ionisation. The chamber counter facilitates counting of "-particles and protons without interference from ~- and 7-particles present at the same time. Up to 1928 the counter had to be used for the counting of 6- and 7-rays. In t h a t year Geiger and Miiller published the improved design of a counter, known today as the GeigerMiiller counter, which was a development of the multiplication counter. This design was improved in 1935 by Trost, by providing a 'self-quenching' effect. The author proceeds to describe the hydraulic design of a spark counter and later developments of this instrument. Methods of counting based on the action of electron multipliers were brought into practical use in 1936 by Zworykin and represent a major deviation from the operating principle employed on previous counters, i.e. from counting methods based on gas ionisation. The article concludes with a description of the scintillation counter originated by Kallmann in 1947. Crystals and liquids which show changes of resistance when particles are incident upon them can also form the basis of counters. Sommaire: On passe en revue l'~volution des compteurs et les caract6ristiques principales de quelques types actuels.
Techniques for Counting Radiokrypton See Abstract No.: 5/IV
65/IV
~2s
Radiocarbon Dating System See Abstract No.: 139/III
Vacuum Tr ^ 7
¥7
Oaober 1955
VACUUM Classified Abstracts
Author Index, Author
Vol. V
(I955)
Title of Publication
Aitken, P. B., et al. Alexander, J., et al. Alexeff, I., et al. Allegheny Ludlum Steel Corp., et al. Allen, F. G., et al. Allen, T. K., et al. Alvarez, L. W . , et al. Andersson, L., et al. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon (A.S.H.). Armour & Co., et al. Atkins, D. F., et al.
New Design of a Vacuum Jacket Precision Combustion Calorimeter. Twenty-Stage Molecular Distillation Unit. Evapor-Ion P u m p Developments. Wrapped Alloy Core Electrode.
Bach, B. B., et al. Bailey, R. A., et al. Bailleuil-Langlais, J. Ballentine, O. M.
Hydrogen in Cast Iron. The Appearance of Some Oscillating Discharges. The Vacuum Obtainable in a Thermionic Valve and Its Measurement. Procedure for Determining Vapour Pressures of Materials of Low Volatility. Use of the Gliding Spark for Spectro Analysis in the Far Ultra-Violet. Improvements r.t. Rotary Vacuum Pumps. Production of Hafnium. High Vacuum Metallising and Toy Manufacture. Gassing of Liquid Dielectrics Under Electrical Stress. How Processing Conditions Affect Micro-Organism Radio-Resistance. Metal-Film Resistance Thermometers for Measuring Surface Temperatures. A Study of Consumable Electrode Arc Melting. Production of Zirconium Alloys by Consumable Electrode Arc Melting. The Magnetically Suspended Equilibrium Ultracentrifuge. Ultra High Vacua. Carbonyl Process.
Balloffet, G., et al. Bancroft, F. E., et al. Barr, M. M., et al. Barrett, A. S. D. Basseches, H., et al. Bates, C. J., et aL Baus, B. V., et al. Beall, R. A., et al. Beall, R. A., et al. Beams, J. w . , a al. Becker, J. A. Bell Telephone Labs. Inc., et aL Bell Telephone Labs. Inc., et al. Bendersky, D. Benner, F. C., et al. Berkeley, F. D. Berkowitz, A. E.
Bernier, J. P.,
et al.
Bernier, J. c., et al. Berry, R . , et al.
October, 1955
Abstr. No. 107/I 132/III 4/II 95/III
Ultra-High Vacuum Valve. 98/II The Appearance of Some Oscillating Discharges. 60/I Berkeley Proton Linear Accelerator. 35/IV Freeze-Drying with a Modified Glick-Malmstrom Apparatus. 30/IV Metallic Coatings on Non-Metallic Materials. IV. Vacuum Coating Methods 4 / I I I Ceramic Twin-Triode Pumping Technique. 23/II Medical Research Council's Cyclotron. 39/IV Evaporated Films--New Use? 44/I The Electron Microscope and Some of Its Industrial Applications. 61/II Finishing Ever Ready Lamps. 71/I Vacuum Brazed Clad Metal Now Commercial Reality. 82/I Applying Test Loads by Vacuum. 84/I Seal-Off Valve for Vacuum Systems. 102/II Vacuum Melting Furnace Installation a t Carboloy Plant. 107/III Vacuum Bushings. 109/II Vacuum Annealing Upgrades Metals ll0/III Precision Casting with Vacuum and I n e r t Gases. ll9/III A Modern Cryogenic Engineering Laboratory. 145/I Good Tomato Powder Made Experimentally. 152/III Giant Chambers Cool Lettuce. 154/III Buhler Vacuum Paste-Goods Device. 156/III Stainless Provides Durability in De-aerators. 158/III 3 Keys to Clear Solution. 160/I Vacuum Flotation for Coal Fines. 160/III Melt Quality Tests. I. Non-Ferrous. 190/I Titanium and Zirconium Tubing Annealed in Vacuum Furnace. 201/I A Metallurgical Study of Molybdenum. Quarterly Status Report. 210/I Aluminised Clothing to Give Heat the Bounce. 216/I TV Chemicals. 55/I Improvements i.o.r.t. Closures for Lyophilisation Containers. 31/IV Electronic Vacuum Dilatometer. 53/II
Electrical Capacitors.
81/1I 60/1
20/I llS/II 651I 20/II 2071I 45/I 12/I 151/I ll0/I 94/III 99/III 55/II 8/I 123/III 48/III
A Special Thermocouple for Measuring Transient Temperatures. Improvements i.o.r.t, the Coating of Threads With Metals. Air Ejectors Cheaper T h a n Steam. Relation to Diffusion Measurements of Some Beta-Ray Absorption Phenomena. A Direct Measurement of the Energy Locally Absorbed from a GammaRay Beam. High Vacuum Pump. Improvements i.o.r.t. Valves. Vacuum Vol. V
75/I 215/I 22/II 97/I 96/I 12/II I01/II
329
IV
--
Special
Subsidiary S u b j e c t s
--
IV
Contd.
of f r a g m e n t s of processed material situated near the opening of the bottle. W h e n air is a d m i t t e d rapidly to the v a c u u m c h a m b e r containing bottles w i t h the closures of the new design the i n r u s h of air will excercise an additional .~orce on the closure such t h a t the k n o b s collapse a n d t h e closure is forced down o n t o the container flange sealing the bottle in t h e process. If t h e v a c u u m c h a m b e r is b r o u g h t u p gradually to atmospheric pressure no seal is m a d e and pressure in the bottle rises to atmospheric. A collar is t h e n placed over the closure a n d crimped u n d e r t h e flange of the container in order to effect a seal. A central hole in this cover facilitates the insertion of an h y p o d e r m i c needle for w i t h d r a w a l of the material w h e n required. F o r normal storage p u r p o s e s the hole is covered u p b y a second cap which in t u r n is held down b y an outer collar, the lower portion of which is crimped u n d e r t h e flange of t h e container. Sommaire: Ce b r e v e t ddcrit u n container de lyophilisation amdliord dans lequel le p r o d u i t est lyophilisd, et stockd aseptiqueraent.
45 - -
ELECTRONICS
--
Ab~tr~t No. and Refereno~
A. D. Holmes & Armour & Co. Brit. Pa~
730,148
45
3211V
High Energy Physics See A b s t r a c t No.: 88/I
Production of Enriched Non-Radioactive Isotopes at Oak Ridge National Laboratory
33/1V
See A b s t r a c t No.: 74/II 34/IV
High Energy Particle Accelerators United Kingdom. The first particle accelerators gave o u t p u t s of a few h u n d r e d keV, b u t m o d e r n machines will soon operate at u p to 20-30 GeV. The lower energy a p p a r a t u s , however, is not obsolete. The article discusses the characteristics of the high-energy machines and the uses to which t h e y m a y be put. All accelerators of highenergy particles use acceleration b y an r.f. field across gaps, except the betatron, which accelerates electrons and uses the electric field associated w i t h a changing magnetic field. Particle stability is the m a i n problem. Firstly, the particles and fields m u s t be as near in phase a t the gaps as possible, and secondly, focusing m u s t be employed to p r e v e n t dissipation of a large n u m b e r of particles. I n linear accelerators a large n u m b e r of gaps in a s t r a i g h t line are used, while the o t h e r t y p e s of machine use a magnetic field to e m p l o y the same gap or gaps repeatedly. The linear accelerator is likely to be the b e t t e r machine for electrons, while the closed orbit machines are p r o b a b l y the best for heavier particles. The synchro-cyclotron is restricted b y the fact t h a t its cost rises rapidly as the energy r e q u i r e m e n t s increase owing to the large m a g n e t required. The p r o t o n s y n c h r o t r o n uses a fixed orbit radius and therefore only an a n n u l a r magnetic field is required, t h u s lowering the cost. The linear accelerator has reached 600 MeV (electrons) using a sectioned corrugated waveguide 60 m. long. Synchro-cyclotrons h a v e delivered p r o t o n s w i t h energies up to 450 MeV. Electron s y n c h r o t r o n s will operate at 5-6 GeV, and the p r o t o n machine a t a b o u t the same level, the orbit radius being a b o u t 18 m. These high energy machines are used for a v a r i e t y of nuclear experiments, of which polarisation effects in the scattering of p r o t o n s b y nuclei, and observation of individual particles of the meson group, are typical examples. Sommaire: Une revue des accdldrateurs de particule, ~ h a u t e dnergie actuellement employds, et t y p e d'expdriences faites avec ces appareils.
Berkeley Proton Linear Accelerator
Article by J. Coekcroft &
T. O. Pickavance Endeavour x4, April 1955 61-70
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United States. I n the historical introduction to their p a p e r the a u t h o r s p o i n t o u t t h a t a l t h o u g h the p r o t o n linear accelerator has n o w been bettered from the cost point of view b y the p r o t o n s y n c h r o t r o n it still h a s a n u m b e r of a d v a n t a g e s over the s y n c h r o t r o n , principally in the characteristics of the external beam. 85% of the b e a m is concentrated within a 3 ram. diam. circle; the angular divergence of the b e a m is 10 "s radian; the energy h o m o g e n e i t y is a b o u t 3 x 10-a; t h e average external b e a m c u r r e n t is a b o u t l0 s times t h a t of the 184-inch cyclotron and the average external b e a m c u r r e n t density is a b o u t 106 times as great. The general design characteristics are discussed with relation to cost, efficiency and safety. The wavelength was chosen to be 150 cm. because r a d a r e q u i p m e n t was available in this range. The p o w e r per unit-length is limited by x - r a y emission and electrical breakdown. I t is observed t h a t layers of p u m p oil are responsible for m o s t of the electron emission. The injection energy was chosen as 4 MeV, this being a reasonable voltage to attain with an electrostatic generat o r and also a high injection energy was desirable to accomplish focusing b y thin beryllium foils. The accelerator consists of 47 individual cavity resonators which h a v e to be individually t u n e d to the same r e s o n a n t frequency. Drift t u b e s are incorporated to shield the p r o t o n s while the field is in the w r o n g direction. A particle takes one full r.f. period to travel between mid-points of successive drift tubes. The a u t h o r s give m a t h e m a t i c a l t r e a t m e n t s for the voltage gain, p o w e r input, Q, and modes of the cavities. The general b e a m d y n a m i c s are considered mathematically. W h e t h e r or not a particle injected into the machine is accelerated t h r o u g h the machine depends on the p h a s e and velocity t h a t it has as the entrance to the machine. A set of curves is given from which the phase acceptance of the particle can be determined. The r e s o n a n t cavity of the accelerator is housed in a steel t a n k 40 ft. long and 48 inch. in diam. The top is hinged, 4 inch. above centre, and can be raised b y a pair of hydraulic cylinders. The v a c u u m gasket used in sealing, r u n s completely r o u n d the t a n k and is 90 ft. long.
October, 1955
Vacuum l'ol. I"
321
VACUUM Classified A b s t r a c t s
Abstract No. and References
Article by L. W. Alvarez, H. Bradner, J. V. Franck, :H. Gordon, J. D. Gow, L. C. Marshall, F. Oppenheimer, W. K. It. Panofsky, C. Riehman & J. R. Woodyard Rev. ~ci. Instrum.
26, Feb. 1955 111-133
36/iv
322
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Special Subsidiary
Subjects
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Contd.
The gasket is of flat-H cross section of moulded r u b b e r and is held to the un-machined flange b y special screws and retained by a ¼-inch square strip of steel, tack-welded to the v a c u u m side of the flange. The t a n k is m o u n t e d on a roller at one end to allow expansion and is prevented from rolling over b y the p u m p manifold which is resting on the floor. The r e s o n a n t cavity is a 'liner' m o u n t e d within the tank. I t is of dodecagon cross section, each face being a long copper strip the length of the liner, s u p p o r t e d on die-formed circumferential frames, in t u r n s u p p o r t e d b y spring s u p p o r t s to the main tank. The liner is also m o u n t e d to allow for expansion. The liner h a s 40 p u m p - o u t slots, 12 inch. long b y ½ inch wide. E a c h liner panel is cooled b y a 40 ft. length of t u b i n g t h r o u g h which w a t e r is circulated. The principle radiations from the accelerator were x - r a y s and fast neutrons. The x - r a y s were reduced to a safe level b y 1½ inch. of lead and the n e u t r o n s b y an 18 inch. thick wall of basalite concrete. X-radiation generally increased after opening the s y s t e m to air. After several m o n t h s r u n n i n g the s y s t e m had to be cleaned of p u m p oil deposits. The v a c u u m r e q u i r e m e n t s are m e t b y a 30-inch. three-stage diffusion p u m p and an 8-inch two-stage diffusion p u m p in series backed b y two 43 c.f.m. K i n n e y r o t a r y p u m p s in parallel. A refrigerated baffling s y s t e m was used. The p u m p i n g speed m e a s u r e d inside t h e liner was 2,500 1./sec. Many different types of v a c u u m seals are used in the s y s t e m including Teflon compression seals in the transmission line input. The machine operates with a total end-to-end voltage of 36 MV. The d u t y cycle is 0.9, the average power is a p p r o x i m a t e l y 20 kW. The oscillator s y s t e m consists of three pre-exciter oscillators and nine single-tube power oscillators, each connected to the liner t h r o u g h a separate transmission line and coupling loop. The correct mode of operation is chosen b y m a n u a l t u n i n g of the pre-exciter oscillators. The magnitude of the load impedance is adjusted b y v a r y i n g the size of the coupling loop in the liner. The power s y s t e m uses a s t a n d a r d three-phase m e r c u r y v a p o u r rectifier circuit charging a pulse-forming n e t w o r k t h r o u g h a reactance. The n e t w o r k is discharged into the load b y a triggered spark gap t h r o u g h a pulse transformer. A separate power s y s t e m feeds the pre-exciter oscillators. The pulse generator supplies a trigger pulse to the Van de Graaff generator which keys the ion source after the cavity is built up. One small m a g n e t deflects electrons formed in the final drift tubes u p w a r d s into a carbon catcher and a larger electro-magnet is used for separating the b e a m h a r m o n i c s and deflecting the b e a m to its desired position. The m e a s u r e d energy available is close to 31.7 MeV. Beam c u r r e n t available is ¼ tLA average, the m a x i m u m recorded being 0.37 ~zA at a recurrence rate of 15 c./sec. S o m m a i r e : Ddtails d ' u n accdl6rateur lin~aire de p r o t o n s opdrant m a i n t e n a n t 5. Berkeley; cet appareil a u g m e n t e l'dnergie des p r o t o n s jusqu'& une 6nergie finale de 31.5 MeV, p a r t a n t d ' u n 6jecteur Van de Graaff de 4 MeV.
Stanford High-Energy Linear Electron Accelerator (Mark III) United States. The Stanford electron accelerator Mark I I I is a travelling-wave accelerator employing 21 klystron amplifiers, feeding separate 10 ft. sections with 10-20 MW of pulsed power of a wavelength of 10.5 cm. The electrons are injected at 50-80 kV and travel 220 ft. in an a p e r t u r e of 2 cm. diam. E x p e r i m e n t a l stations are provided at points 10 ft., 100 ft. and 125 ft., along the accelerator as well as at three positions a t the end. A simple explanation of the principle of operation of a travelling-wave accelerator is given and it is pointed o u t t h a t the electron after the first few inches reaches nearly the velocity of light and thereafter the gain in energy of the electron is shown by a gain in mass. At the design values of 1=220 ft. and V = I , 0 0 0 MeV the electron 'sees' the accelerator as being 26 cm. long whereas the a p e r t u r e r e m a i n s relativistically unaltered. The acceler a t o r s t r u c t u r e is of the disc-loaded t y p e and the choice of the various design p a r a m e t e r s is discussed with a view to as high an o u t p u t as possible. These factors include materials, configuration, disc spacing, disc thickness, power distribution and frequency. The filling time for the s t r u c t u r e is chosen as 1 ~ sec. leaving 1 ~t sec. as the accelerating time when using 2 ~ sec. pulses. Special klystron amplifiers were developed which are synchronised b y supplying t h e m from a c o m m o n source. A single master-oscillator provides the necessary trigger pulses to operate the various pulsed components. A phase-shifter in the i n p u t to each klystron is adjusted to maximise the b e a m o u t p u t . The e a r t h ' s magnetic field is minimised b y w r a p p i n g the accelerator with hypersil and also b y degaussing coils. E a c h accelerator section is made up from five 2-ft. subsections made b y shrinking 23 copper discs in a prepared copper tube. The fabrication of the accelerator subsections is described in detail laying stress on the importance of attaining great accuracy and repeatability. A micro-wave m e a s u r i n g technique is used to check the internal diameter of the t u b i n g after machining and honing. I n the shrinking operation the tube is placed in a s t e a m jacket; the discs, m o u n t e d on an inner mandrel, are immersed in liquid nitrogen and t h e n the two are fitted together and allowed to reach r o o m temperature. The mandrel is r e m o v e d and the flanges at either end of the t u b e are machined to provide an O-ring slot which can be p u m p e d t h r o u g h a small hole to provide a g u a r d - v a c u u m space between the lapped ends of the section and the O-ring. The completed section is t h e n s u b m i t t e d to r.f. tests for m e a s u r e m e n t of phase velocity, group velocity, Q, impedance and reflections, m a t c h i n g of couplers and m e a s u r e m e n t s of imperfections. The klystrons are continuously p u m p e d to a pressure of a p p r o x i m a t e l y 10 -5 mm. Hg, when the cathode is hot. The accelerator v a c u u m is governed b y two factors, electrical b r e a k d o w n and electron scattering, and is a p p r o x i m a t e l y 2 x 10 "4 mm. H g when the accelerator is r u n n i n g at full power. The klystrons were specially developed for the application. The design is such t h a t the valve is d e m o u n t a b l e for replacement of the cathode b u t a sealed-off design is t h o u g h t to be feasible. The accelerator is fed by 21 klystrons, the p o w e r to each one of which is synchronised allowing for the time of flight of electrons t h r o u g h the accelerator. Power is transferred from the klystrons to the accelerator t h r o u g h an evacuated (10 -5 ram. Hg) waveguide. The klystrons are separated from the amplifier b y ceramic w i n d o w s brazed into the waveguide. Each 10 ft. section of accelerator is p u m p e d by a small oil diffusion p u m p t h r o u g h the i n p u t waveguide with a liquid nitrogen t r a p and a water-cooled baffle between p u m p and waveguide. Continuous monitoring of pressure is accomplished b y using ionisation gauges which are also used to give a l a r m in case of v a c u u m failure. Isolation valves of a special design are used to isolate 10 ft. sections for serviceing purposes. The g u a r d - v a c u u m between O-rings and lapped surfaces at the end of each accelerator section is obtained using a mechanical p u m p . The problem of injecting the electrons into the accelerator is discussed
Vacuum Vol. V
October, 1985
VACUUM Classified A b s t r a c t s
IV --
Special
Subsidiary
Subjects
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IV
Abstract No. and Referencea
Contd.
m a t h e m a t i c a l l y a n d d e s c r i p t i o n s a r e g i v e n of t h r e e t y p e s of g u n a n d p u l s i n g circuits w h i c h were tried. T h e g u n c u r r e n t l y in u s e is of t h e directly h e a t e d t u n g s t e n spiral t y p e d e v e l o p e d a t T e l e c o m m u n i c a t i o n s R e s e a r c h E s t a b l i s h m e n t , E n g l a n d . A t h e o r e t i c a l s t u d y of b u n c h e r s a n d b u n c h e r design is given. F a c t o r s c a u s i n g t r a n s v e r s e m o t i o n of t h e electron b e a m w i t h i n t h e accelerator are considered. A p a r t f r o m t h r e e i n t e r m e d i a t e t a p p i n g p o i n t s t h e m a i n b e a m is deflected b y m a g n e t s a t t h e e x i t of t h e accelerator to give electron b e a m s s u b s t a n t i a l l y free f r o m x - r a y s a n d n e u t r o n s b y either t h e ' a c h r o m a t i c p r i s m ' s y s t e m or t h e ' a c h r o m a t i c t r a n s l a t i o n ' s y s t e m . R a d i a t i o n shielding p r o b l e m s f r o m s u c h a h i g h e n e r g y accelerator are serious a n d are discussed fully. T h e principle sources of r a d i a t i o n h a z a r d are x - r a y s a n d n e u t r o n s . Discussion of n e u t r o n e n e r g y d i c t a t e s t h a t 5 ft. of concrete is n e c e s s a r y to r e d u c e t h e level to safe limits. A g r a d e d shield of concrete is u s e d for p r o t e c t i o n f r o m x - r a y s , ~,-rays a n d electrons, b e i n g 2 ft. t h i c k of o r d i n a r y concrete a t t h e i n p u t e n d a n d 3 ft. t h i c k of ferrite-loaded concrete a t t h e o u t p u t end. T h e m a x i m u m e n e r g y a t t h e t i m e of w r i t i n g w a s 630 MeV, t h e m a x i m u m a v e r a g e c u r r e n t is 1.0 I~A, m a x i m u m p e a k c u r r e n t is a b o u t 50 m A , t h e cross section of t h e b e a m is ¼ i n c h d i a m . a n d t h e b u l k of t h e e n e r g y is in a 2 % e n e r g y b a n d . T h e c u r r e n t available a t i n t e r m e d i a t e p o i n t s is h i g h e r t h a n a t t h e end. Sommaire: D6tails s u r u n acc616rateur lin6aire d'61ectrons, ~ h a u t e Snergie (Mark III) install6 h l ' U n i v e r s i t ~ de S t a n f o r d , ainsi q u e de s o n & t u i p e m e n t d'acc616ration, de t r a n s m i s s i o n de p u i s s a n c e radio-fr6quence, appareil auxilliaire, d y n a m i q u e s d u faisceau e t c e r t a i n s r 6 s u l t a t s s u r son f o n c t i o n n e m e n t .
Article by M. Chodorow, E, L. Ginzton, W. W. Hansen, R. L. Kyhl, R. B. Neal, W. K. H. Panofsky e2al. Rev. Sci. I ~ . a6z Feb. 1955 134-204
A Linear Accelerator for X - R a y Therapy See A b s t r a c t No.: 22/I
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Developments in Apparatus for Deep X - R a y Therapy See A b s t r a c t No.: 149/I
3s/Iv.
Medical Research Council's Cyclotron United Kingdom. T h e M.R.C. c y c l o t r o n a t H a m m e r s m i t h H o s p i t a l is to p r o d u c e b o t h n e u t r o n a n d c h a r g e d particle r a d i a t i o n , a n d radio-isotopes for t h e r a p y a n d research. T h e c y c l o t r o n is a 45-inch m a c h i n e , t h e m a g n e t core c o n s i s t i n g of e i g h t pieces. R e c t a n g u l a r a l u m i n i u m t u b i n g is u s e d for t h e c o n s t r u c t i o n of t h e coils (408 t u r n s each), a n d cooling is b y distilled w a t e r t h r o u g h t h i s t u b i n g . A s e p a r a t e h e a t e x c h a n g e r u s i n g t a p w a t e r cools t h e distilled w a t e r , t h e t a p w a t e r c i r c u l a t i n g t h r o u g h e v a p o r a t o r cooling towers. A field s t r e n g t h of 17 k g a u s s is o b t a i n e d across a n effective g a p of 8 inch. T h e lids of t h e v a c u u m b o x f o r m t h e pole faces ( ' A r m c o ' iron, 3 inch. thick, copper p l a t e d on t h e inside face). T h e v a c u u m b o x itself is of rolled brass, b r a z e d t o g e t h e r . T h e ' d e e ' s y s t e m is c o n v e n t i o n a l , a n d o p e r a t e s a t 11,286 Mc./sec. T h e m e a s u r e d Q is 4,550. T h e ion source is of the h o o d e d t y p e a n d h a s a vertical h a i r p i n f i l a m e n t fed f r o m a 500A 6V generator. T h e p u m p i n g a g g r e g a t e c o n s i s t s of t w o 16-inch diffusion p u m p s b a c k e d b y t w o m e c h a n i c a l p u m p s of 200 c u . f t . / m i n , c a p a c i t y . W i t h r e f r i g e r a t e d baffles t h e speed is 4,000 1./see. a t 10 "5 m m , H g for a v o l u m e of 4,000 1. Distilled w a t e r cooling is e m p l o y e d , a n d 5 / 10 "s ram. H g c a n be r e a c h e d in 2 hr, a n d 5 x 10 "6 ram. H g in 2 d a y s . T h e leak r a t e h a s b e e n m e a s u r e d a t 6 m i c r o n s p e r h o u r . T h e r.f. s y s t e m c o n s i s t s of a 12 k W t r a n s m i t t e r d r i v i n g t w o n e u t r a l i s e d B W 165 v a l v e s of 22.5 k W a n o d e dissipation. T h e o u t p u t a t t h e f r e q u e n c y s t a t e d is 75 k W . T h e m a c h i n e will give a 30 MeV ~-particle b e a m , a n d b e a m c u r r e n t s of 750 ~A of singly c h a r g e d h y d r o g e n m o l e c u l a r ions h a v e b e e n m e a s u r e d a t 6 i n c h radius. Sommaire: D e s c r i p t i o n d ' u n c y c l o t r o n install6 ~ l ' H S p i t a l d ' H a m m e r s m i t h p o u r la p r o d u c t i o n de n e u t r o n s , ou de r a d i a t i o n charg6es de p a r t i c u l e s et d ' i s o t o p e s radio-actifs.
39/Iv
Article by ~Luon. E~n~ x99, 17.6.1955 846-847
The x56-inch. Cyclotron at Liverpool United Kingdom. T h e e s s e n t i a l f e a t u r e s a n d u s e of t h e 156-inch. s y n c h r o - c y c l o t r o n a t Liverpool U n i v e r s i t y a r e described. T h e b u i l d i n g of t h e m a c h i n e w a s i n s t i g a t e d b y Sir J a m e s C h a d w i c k a n d its c o n s t r u c t i o n w a s c o m pleted in t i m e for t h e r e g u l a r e x p e r i m e n t al p r o g r a m m e c o n c e r n e d w i t h t h e p r o p e r t i e s of f a s t p r o t o n s , n e u t r o n s a n d pious, to begin in J a n u a r y , 1955. T h e b u i l d i n g h o u s i n g t h e m a c h i n e consists of t h e t w o - s t o r e y c y c l o t r o n r o o m w i t h a large a n t e - r o o m u s e d for e x p e r i m e n t a l w o r k . A b o v e t h e s e are s i t u a t e d v e n t i l a t i o n a n d cooling e q u i p m e n t . T h e c y c l o t r o n r o o m is h e a v i l y screened b y t h i c k concrete walls a n d s a n d s t o n e p a c k i n g , w i t h c h a n nels p r o v i d e d t h r o u g h t h e 12 ft. t h i c k concrete wall to allow b e a m s of particles to e n t e r t h e a n t e - r o o m . T h e m a g n e t h a s poles of 13 ft. d i a m . T h i s d i a m e t e r w a s d e t e r m i n e d b y t h e p l a n t a v a i l a b l e in B r i t a i n for t h e m a c h i n ing. T h e energising coils for t h e m a g n e t are cooled w i t h w a t e r c i r c u l a t i n g in t h e c o n d u c t o r , a n d p r o d u c e a c e n t r e field of 18,900 g a u s s c o r r e s p o n d i n g to a p r o t o n e n e r g y of 410 MeV. T h e g a p is 15.5 inch. n e a r t h e c e n t r e a n d ] 1.5 inch. a t t h e edge. T h e r.f. s y s t e m is similar to t h e t h r e e - q u a r t e r w a v e s y s t e m u s e d b y M a c K e n z i e (Berkeley) w h e r e t h e dee is coupled t h r o u g h a section of t r a n s m i s s i o n line to a v a r i a b l e c a p a c i t y , t h e o t h e r side of w h i c h is c o n n e c t e d t h r o u g h a s t u b line to earth. T h e dee is s u s p e n d e d in t h e v a c u u m t a n k . T h e t o t a l v o l u m e to be e v a c u a t e d is 30,000 1. a n d t h e p r e s s u r e c a n be r e d u c e d to 3 x 10 -6 ram. H g b y t w o 80-cm. m u l t i - s t a g e oil diffusion p u m p s w i t h a c o m b i n e d speed of 24,000 L/see. a t 10 -4 ram. Hg. As in-leakage of h y d r o g e n is necessary, t h e o p e r a t i n g p r e s s u r e is higher, i.e. 5 x 10 "5 ram. H g . T h e m e a n b e a m c u r r e n t is over 1 ~tA f r o m w h i c h a n ext r a c t e d b e a m of p r o t o n s of 383 MeV a n d a c u r r e n t of 3 × 10 "t I~A is available in t h e e x p e r i m e n t a l room. N e u t r o n s of energies 200-400 MeV are available, a n d b e a m s of pious of 150 M e V a n d 96 MeV m a y be e x t r a c t e d f r o m t h e tank. Sommaire: D e s c r i p t i o n des p a r t i e s essentielles et de r e m p l o i d ' u n s y n c h r o - c y c l o t r o n de 156 inches install~ ~t l ' U n i v e r s i t ~ de Liverpool.
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Article by M. J. Moore 2Vature x75 , 11.0.1955 1012-1015 •
October. 1955
V~cuum Vol. V
a
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Note b y K. E. A. Effat & J. H. Fremlin J. Be/. I marum. 32, Sept. 19{~5 363-364
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Special Subsidiary Subjects - Contd.
IV
A Circulation-System for He-3 United Kingdom. Reference is m a d e to e x p e r i m e n t s occasionally carried o u t in t h e B i r m i n g h a m 60-inch cyclotron e m p l o y i n g ions of helium-3. H e l i u m - 3 occurs in t h e a t m o s p h e r e as one p a r t p e r million a n d t e n t i m e s less in well-helium. H e l i u m , enriched w i t h t h e isotope of m a s s 3 to 2~/o, c a n be o b t a i n e d b u t is expensive. F o r t h a t reason a s y s t e m h a s been devised for t h e h e l i u m e m p l o y e d in e x p e r i m e n t s to be collected from t h e cyclotron, purified a n d recirculated to t h e i n s t r u m e n t . T h e s y s t e m m a k e s use of t h e fact t h a t charcoal cooled to liquid air t e m p e r a t u r e a b s o r b s all gases b u t h e l i u m . I n detail, t h e all-metal s y s t e m consists of a m e c h a n i c a l r o t a r y p u m p (disconnected while t h e h e l i u m is circulated), a n d t w o 14-inch off diffusion p u m p s o p e r a t i n g in parallel to e v a c u a t e t h e c y c l o t r o n v a c u u m c h a m b e r , b a c k e d b y a 1-inch m e r c u r y diffusion p u m p . A liquid air t r a p in f r o n t of t h e m e r c u r y diffusion p u m p r e m o v e s w a t e r a n d oil v a p o u r f r o m t h e s y s t e m . T h e m e r c u r y diffusion p u m p ejects t h e circulating g a s into t h e charcoal t r a p w h i c h consists of a s t a i n l e s s steel U - t u b e c o n t a i n i n g 35 g. of a c t i v a t e d charcoal cooled b y liquid air. A second m e r c u r y diffusion p u m p m a i n t a i n s a p r e s s u r e g r a d i e n t across t h e charcoal a n d r e t u r n s t h e purified h e l i u m t h r o u g h a needle v a l v e to t h e c y c l o t r o n source. W i t h t h e n o r m a l air leak (1-2 c.c./min, a t a t m o s p h e r i c pressure) t h e c i r c u l a t i n g o p e r a t i o n c a n be m a i n t a i n e d for 8 hr. w i t h o u t u n d u e rise of t h e n o r m a l o p e r a t i o n a l p r e s s u r e w h i c h is 3 × 10 -6 m m . H g . On c o m p l e t i o n of a r u n t h e g a s e s a b sorbed in t h e charcoal t r a p , w h i c h s h o u l d a m o u n t to a b o u t ½ 1. of air a t a t m o s p h e r i c pressure, are r e m o v e d b y h e a t i n g t h e t r a p to 400°C. T h e g a s e s liberated are w i t h d r a w n b y m e a n s of a n a u x i l i a r y p u m p . Sommaire: Description d ' u n s y s t ~ m e p o u r rc~cup~rer et recirculer l'h61ium; ce s y s t ~ m e est employ~ p o u r c e r t a i n s t r a v a u x avec le cyclotron de 60 inches de B i r m i n g h a m .
42]IV
Radioisotope Production Rates in a zz-MeV Cyclotron See A b s t r a c t No.: 142/III
43/IV
S o m e Properties of a Simple O m e g a t r o n - T y p e M a s s Spectrometer See A b s t r a c t No.: 4 7 / I I
44/IV
Theory and Probe Measurements in a Magnetic Ion Source Belgium. A m a g n e t i c ion source is described consisting of a cylindrical t u b e (the anode) p a r t i a l l y closed a t each e n d b y a disc p e r f o r a t e d a t t h e centre. E a c h of t h e s e holes o p e n s into a s h o r t cylindrical c h a m b e r of t h e s a m e d i a m e t e r as t h e anode; in one c h a m b e r is t h e f i l a m e n t w h i c h serves as t h e source of electrons, in t h e o t h e r a F a r a d a y cylinder for t h e e x t r a c t i o n of ions a n d a p a s s a g e to t h e p u m p i n g s y s t e m . H a l f - w a y a l o n g t h e a n o d e is a side t u b e c o n t a i n i n g a L a n g m u i r p r o b e carried b y a s p r i n g - r e t a i n e d iron piston. B y m e a n s of a m a g n e t , t h e probe c a n be m a d e to p r o t r u d e into t h e a n o d e t u b e to i n v e s t i g a t e t h e potential, etc., a t v a r i o u s p o i n t s a l o n g t h e d i a m e t e r of t h e anode. B o t h e n d - p l a t e s a n d c h a m b e r s are e a r t h e d , while t h e a n o d e is c o n n e c t e d t h r o u g h a resistor a n d a c u r r e n t m e t e r to a positive poten*,_'al. T h e probe c a n be m a d e either positive or negative, a n d h a s its o w n v o l t m e t e r a n d a m m e t e r . T h e whole t u b e fits inside a pair of H e l m h o l t z coils w h i c h p r o d u c e a n axial m a g n e t i c field. T h e f i l a m e n t a n d one e n d - p l a t e a c t as t b e c a t h o d e a n d e m i t e l e c t r o n s a l o n g t h e axis of t h e anode; t h e electrons oscillate in t h e c o m b i n e d electric a n d m a g n e t i c fields a n d c a u s e ionisation of t h e g a s filling. A t h e o r y is o u t l i n e d l e a d i n g to e q u a t i o n s for t h e densities of electrons a n d ions as f u n c t i o n s ~f d i s t a n c e from t h e axis, in t h e ' n o r m a l s t a t e ' (ionic d e n s i t y neglected) a n d in t h e ' s u p e r s t a t e ' (ionic a n d electronic densities r o u g h l y equal). P r o b e c h a r a c t e r i s t i c s were i n v e s t i g a t e d e x p e r i m e n t a l l y for t h e s u p e r s t a t e ; w i t h a cylindrical probe t h e ionic b r a n c h of t h e characteristic w a s f o u n d to be similar to t h a t for o r d i n a r y discharges, w i t h t h e s q u a r e of t h e c u r r e n t falling linearly w i t h increasing positive p o t e n t i a l . T h e r e s u l t s of t h e e x p e r i m e n t s , perf o r m e d w i t h m e r c u r y v a p o u r , were f o u n d to agree w i t h t h e theoretical prediction of ionic or electronic d e n s i t y as a G a u s s i a n f u n c t i o n of d i s t a n c e f r o m t h e axis. B y c o m p a r i n g t h e radial d i s t r i b u t i o n of t h e space p o t e n t i a l w i t h t h e a c t u a l a n o d e potential, t h e q u a n t i t y k T + / q w a s e v a l u a t e d , a n d h e n c e T + , t h e ionic t e m p e r a t u r e ( k = B o l t z m a n n ' s C o n s t a n t , q = i o n i c charge). V a l u e s of T + as h i g h as 720,000°K h a v e been found. T h e electronic b r a n c h of t h e c h a r a c t e r i s t i c w a s f o u n d difficult to i n t e r p r e t . Sommaire: O n a ~tudi~ e x p 6 r i m e n t a l e m e n t et t h $ o r i q u e m e n t le ' s u p e r s t a t e ' d u n s u n e source m a g n ~ t i q u e d'ion.
Article by M. Hoyaux, R. Lema;tre & P. Gsns
J. Ap'pl. Phya. a6, Jan. 1955 110-112
$24
IV
45/iv
Plutonium: Evaporation Tests, Ionisation Potential and Electron Emission See A b s t r a c t No.: 112/I
46/iv
Uniform Field Breakdown" in A i r See A b s t r a c t No.: 63/1
47/iv
Electrical B r e a k d o w n a t V e r y L o w G a s Pressures See A b s t r a c t No.: 62/I
Vacuum Vol. V
October, 1966
VACUUM Classified Abstracts
IV
-
-
Special Subsidiary Subjects --
IV
Contd.
Artificial Increase of Electrical Breakdown S t r e n ~ h of Air at Low Pressure in the R e . o n of 300 Mc./s. United Kingdom. Experiments carried out in the past applying high frequency energy to an electrode system separated by a small air gap at low pressures (59 ram. Hg and upwards) proved t h a t the use of a d.c. bias voltage can delay the electrical breakdown. The authors report on fresh experiments extending the study to the pressure range 5-120 ram. Hg and using gap widths from 1-4 ram. Two frequencies were employed, 227 and 379 Mc./sec. The d.c. bias voltages ranged from 0-125V. Breakdown will be effected eventually if the life of the free electrons in the gap is longer t h a n half a period of the applied high frequency stress, thus facilitating the building up of an electron avalanche. Where these conditions exist, the presence of a d.c. bias voltage causes the withdrawal of free electrons, which may otherwise contribute to avalanche formation from the gap, by attracting t h e m to the anode. A graph is shown giving the results for a series of experiments carried out a t a pressure of 20 ram. Hg and a high frequency energy of 378.5 Mc./sec. The phenomenon described can be used in practice to inhibit breakdown in electronic equipment operating a t high altitudes. Sommaire: Le phdnombne par lequel un courant continn moddr6 s u p e r p o ~ sur une ultra haute fr~quence appliqu6e ~ un espace variant de 1 ~ 4 mm. sous pressions de l'ordre de 5 ~ 120 mm. Hg, augmente considdrablement la tension de claquage ~ haute fr&quence.
Role of Positive Ions in High-Voltage Breakdown in Vacuum United States. I t has been suggested t h a t one of the more important processes contributing to high voltage breakdown between metallic electrodes in vacuum is electron emission from the cathode due to positive ion bombardment. The results so far obtained cannot be properly correlated because of the varying experimental methods. The study reported in the present article was essentially concerned with three basic factors governing electron emission caused by positive ion bombardment: (a) The effect of high extractive cathode gradlants, (b) the effect of different metallic targets and (c) the effect of different positive ions. Details of the experimental set-up are given. An ion beam of 0.07 [~A, produced by electrons emitted from a ring-shaped tungsten filament on a cup shaped anode, were passed into the acceleration gap, hitting an electrode at earth potential. The latter consisted of a disc which could be rotated and in which were, alternatively, a ½-inch hole and three ½-inch insulated targets of different metals. If the hole w a s placed in the path of the ion beam the latter was collected in a Faraday cage positioned underneath the disc-shaped electrode. The cathode gradient and the total ion energy could be varied by adjusting the terminal voltage and the gap length. The pressure in the system was 6 X I0 "i mm. Hg and total gap voltages ranged from 10 to 140 kV. The experiments were conducted either in helium, hydrogen, nitrogen, xenon, or mercury. Targets of magnesium, aluminium, steel, copper, gold and lead were employed. In each case initial rapid rise of electron emission with ion energy was followed by a slowlinear increase. The emission from aluminium and magnesium target bombardment with helium ions varied slightly with cathode gradient but the emission of other targets such as lead and gold was independent of the value of the cathode gradient. Minimum electron emission was obtained for materials, the atomic number of which was about 40 and the density of which was in the ~eighbourhood of 9 g./c.c. The highest numbers of electrons produced by a positive ion was obtained in bombarding steel with nitrogen ions. By inclining the target to the electron beam the emission could be increased. For an angle of 30 ° between ion beam and target surface the emission was doubled. Previous workers have established t h a t the positive ion emission from metals bombarded by electrons is less t h a n one ion per 1,000 electrons (coefficient A). In this work, it was found t h a t less than twenty electrons are released per impinging positive ion (coefficient B). The particle-interchange theory of high-voltage breakdown in vacuum stipulates t h a t A × B > 1 to produce the required instability to initiate a chain reaction causing eventual vacuum breakdown. The present experiments proved t h a t the secondary electron emission was quantitatively inadequate to fulfil this condition. The present investigation however does not take into account the possible formation of negative ions. Also the outcome of the experiments does not exclude the possibility t h a t vacuum breakdown is caused b y larger atomic aggregates than simple gaseous ions and reference is made in this connection to Cranberg's 'clump' theory of vacuum breakdown (see Volume I I Abstract No. 60/IV. (See also Abstract No. 50/IV.) Sommaire: On a mesurd l'dmission dlectronique de cibles de magndsium, aluminium, cuivre pur, or et plomb, soumises ~ un bombardement d'ions de diff6rents gaz.
Composition of t h e Interelectrode Prebreakdown Current in High Vacuum United States. The study reported in the present article is connected with the work recorded in Abstract No. 49/IV and is concerned essentially with the composition of the interelectrode prebreakdown current. Details of the experimental set-up are given. Measurements were taken on a pair of aluminium electrodes and a pair of steel electrodes. One of the two electrodes was of low heat capacity and thermally insulated, and the other was of large heat capacity remaining a t substantially constant temperature throughout an experimental run. T h e gap between the two electrodes was ~ inch, the high voltage source was a Van de Graaff generator and the gap voltages used were 80-100 kV. The pressure was 5 × 10" ram. Hg. By measuring the rate at which the temperature of the heat insulated electrode rose, the relative amount of prebreakdown current carried b y negatively and positively charged particles passing through the gap could be ascertained. The experiments indicated t h a t the prebreakdown current was composed chiefly of negatively charged particles. In the case of the alumiuium electrode the electrons outnumbered the positive ions by more than 300:1, and in the case of the steel electrode the figure was 1,000:l. I t was established in previous studies t h a t about 1,000 electrons are required for t h e emission of one positive ion. In the work recorded in the previous abstract it was found t h a t no more t h a n twenty electrons were produced b y one impinging positive ion. I t appears t h a t the predominantly negative
October, 1955
Vacuum Vol. V
Ab~.~t No. and Referenoes
is/iv
Letter by G. W. E. Stark & G. L. Fougere Nature x74, 4.12.1964 1066
49/Iv
Artiole by H. C. Bourns, Jr., R. W. Cloud & J. G. Trump J. Appl. Phys. a6, May 1955 596-599
~o/Iv
325
VACUUM Classified A b s t r a c t s
Abstract No.
IV
and Referenees
Article by H. C. Bourne, Jr., J. A~pl. Phys. • 6, May 1955 625-626
5~/IV
Note by P. F. Browne PTo¢. Phys. 8oe. 68B, Aug. 1955 564-566
Special
Subsidiary Contd.
Subjects
m
IV
emission e s t a b l i s h e d in t h e p r e s e n t e x p e r i m e n t s m u s t be c a u s e d b y a d d i t i o n a l m e c h a n i s m s s u c h as field e m i s s i o n o p e r a t i v e in t h e c o n d i t i o n s s t a t e d . Sommaire: D e s m e s u r e s s u r l ' a u g m e n t a t i o n de t e m p e r a t u r e d ' u n e 61ectrode s o u m i s e ~ d e s t e n s i o n s de l'ordre de 80 ~ 100 k V m o n t r e q u e le c o u r a n t de pr~-claquage est compos6 p r i n c i p a l e m e n t de p a r t i c u l e s charg6es n 6 g a t i v e ment.
The Transfer of Metal Between Electrodes in a H i g h V a c u u m on Application of a H i g h Electric Field Eire. D e t a i l s are given of a series of e x p e r i m e n t s c o n d u c t e d for t h e p u r p o s e of c h e c k i n g C r a n b e r g ' s t h e o r y of t h e i n i t i a t i o n of h i g h v a c u u m electric b r e a k d o w n (see V o l u m e II A b s t r a c t No. 60/IV). T w o electrode s y s t e m s were u s e d : (a) W i r e a n o d e - - p l a n e c a t h o d e a n d (b) p l a n e a n o d e - - p l a n e cathode. T h e m a t e r i a l w a s nickel or lead a n d the a n o d e s were coated w i t h deposit of =-active p o l o n i u m of a d e n s i t y of 10 xl a t o m s p e r s q . c m . T h e t r a n s f e r of p o l o n i u m w a s recorded b y m e a n s of a n u c l e a r plate. T h e g a p e m p l o y e d w a s 1 ram. a n d d.c. v o l t a g e s u p to 80 k V were applied. C l u m p s f o r m e d on t h e c a t h o d e a t v o l t a g e s below a n d a b o v e t h e s p a r k i n g voltage. A t large g a p s occasional s p a r k s occurred w i t h o u t p r o d u c i n g c l u m p s . I t w a s f o u n d t h a t a h i g h field r a t h e r t h a n a h i g h v o l t a g e was c a u s i n g t h e i r a p p e a r a n c e . C u r r e n t s of 10"lSA for 1 m i n . resulted in c l u m p f o r m a t i o n . T h e area covered b y e a c h c l u m p w a s less t h a n 10 "~ sq.cm. T h e e x p e r i m e n t s i n d i c a t e d t h a t positive ions f o r m e d from t h e p o l o n i u m d e p o s i t on t h e a n o d e f o r m e d c l u m p s on t h e c a t h o d e on being d r a w n to p o i n t s of field emission. Conditions m o r e t y p i c a l of t h e C r a n b e r g c l u m p e x p l a n a t i o n were f o u n d in a special e x p e r i m e n t w h e r e t h e a n o d e consisted of a s h a r p e n e d t i p of a nickel wire 0.053 cm. d i a m , a n d a p l a n e c a t h o d e , t h e g a p b e i n g 0.025 cm. N i n e t e e n c l u m p s were f o u n d in a n a r e a of a b o u t 1 sq.cm, of t h e cathode. T h e effect of solid c l u m p s b e i n g d e t a c h e d f r o m t h e anode m a y be p r o d u c e d b y electrostatic forces. A calculation in t h e p a r t i c u l a r case i n d i c a t e d t h a t t h e electros t a t i c s t r e s s a t t h e a n o d e a t b r e a k d o w n agreed well w i t h t h e tensile s t r e n g t h of t h e electrode. I n a n o t h e r series of e x p e r i m e n t s t w o p l a n e electrodes were u s e d b u t t h e c a t h o d e w a s c o a t e d w i t h t h e p o l o n i u m deposit. I n t h i s e x p e r i m e n t , too, c l u m p f o r m a t i o n w a s observed. T h e r e w a s a series of s m a l l e r a n d a series of larger c l u m p s on t h e cathode, a n d in a d d i t i o n a n u m b e r of c l u m p s on t h e anode. I n t h i s case t h e c l u m p s c a n n o t h a v e been f o r m e d b y m a t e r i a l t r a n s f e r as o n l y t h e c a t h o d e w a s radioactive. I t is believed t h a t p o l o n i u m ions, f o r m e d b y positive ion b o m b a r d m e n t of t h e cathode, c o n c e n t r a t e in p o i n t s of field emission. T h i s will e x p l a i n w h y t h e r e are s m a l l and large c l u m p s on t h e r a d i o a c t i v e c a t h o d e . T h e c l u m p s o b s e r v e d on t h e n o n - r a d i o a c t i v e a n o d e m a y originate b y m a t e r i a l t r a n s f e r f r o m s u c h p o i n t s on t h e c a t h o d e s u r f a c e w h e r e electron emission, w h i c h c a u s e s t h e conceno t r a t i o n of p o l o n i u m ions in t h e f o r m of a m a j o r c l u m p , is i n t e n s e e n o u g h to m e l t or d i s r u p t t h e c a t h o d e surface. T h e r e s u l t s of t h e l a t t e r series of e x p e r i m e n t s i n t r o d u c e s a n e l e m e n t of d o u b t i~ato t h e t r u e origin of c l u m p s as conceived b y Cranberg. Sommaire: O n a ~tudi6 le t r a n s f e r t de m ~ t a l e n t r e ~lectrodes, sous vide pouss6.
52/iv
Work Function of Tungsten Single Crystal Planes Measured b y the Field Emissioh Microscope See A b s t r a c t No.: 60/II
53/xv
The Effect of Gases on the Contact Potentials of Evaporated Metal F i l m s United States. T h e effect w i t h t i m e of o x y g e n , nitrogen, w a t e r v a p o u r a n d air on t h e c o n t a c t p o t e n t i a l differences b e t w e e n aged b u l k p l a t i n u m a n d e v a p o r a t e d m e t a l films w a s s t u d i e d b y t h e v i b r a t i n g c o n d e n s e r m e t h o d . T h e m e t a l s u s e d were a l u m i n i u m , lead, nickel, c h r o m i u m a n d iron. B o t h reversible a n d irreversible effects were observed. A n e x p l a n a t i o n is offered b a s e d on s o r p t i o n of t h e g a s e s w h i c h p r o v i d e either a dipole barrier or a n ion barrier to t h e emission of electrons. (Authors) Sommaire: O n a 6tudi6 les effets d a n s le t e m p s , de l'oxyg~ne, azote, v a p e u r d ' e a u et air s u r les diff6renees de potentiel de c o n t a c t e n t r e p l a t i n e b r u t vieilli et films de m ~ t a l 6vapor6s.
Article by N. Haekerman & E. H. Lee J. Phys. Chem. 59, Sept. 1955 900-906
54/iv
326
--
A Demountable Vacuum System for Secondary Emission Studies See A b s t r a c t No.: 21]I
55/Iv
Improvements i.o.r.t. Vacuum Tight Joints See A b s t r a c t No.: 106/II
56/Iv
Ceramic-to-Metal Sealing See A b s t r a c t No.: 87/II
57/IV
Ceramic Twin-Triode Pumping Technique See A b s t r a c t No.: 23/II
Vacuum Vol. V
October, 1955
VACUUM Classified A b s t r a c t s
IV
Special Subsidiary Subjects --
IV
Contd.
The Vacuum Valve and Semiconductors France. A l t h o u g h s o m e of t h e r e l e v a n t p r o p e r t i e s of s e m i c o n d u c t o r s h a v e b e e n k n o w n for s o m e t i m e , it w a s t h e i n v e n t i o n of t h e t h e r m i o n i c triode v a l v e in 1913 w h i c h f o r m e d t h e f o u n d a t i o n s t o n e of electronics as we k n o w it t o d a y . H o w e v e r , t h e i n v e n t i o n of t h e t r a n s i s t o r in 1948 h a s a d d e d a n e w a n d i m p o r t a n t b r a n c h to electronic science. T h e p r e s e n t p a p e r p r e s e n t s a c o m p a r a t i v e e v a l u a t i o n of t h e t h e r m i o n i c v a l v e a n d t h e t r a n s i s t o r . I n t h e t h e r m i o n i c valve, e l e c t r o n s or ions are m o v i n g freely on a n e s s e n t i a l l y u n i m p e d e d p a t h . I n t h e t r a n s i s t o r t h e e l e c t r o n s a r e 'tied' to t h e m e d i u m in w h i c h p r o p a g a t i o n t a k e s place a n d t h i s m e d i u m exercises a n appreciable r e s i s t a n c e to a n y forces a p p l i e d e x t e r n a l l y . T r a n s p o r t of electricity in t h e t h e r m i o n i c v a l v e is e s s e n t i a l l y obt a i n e d a t t h e e x p e n s e of a p p l y i n g g r e a t e n e r g y in t h e f o r m of h e a t , t h e d i s s i p a t i o n of w h i c h o f t e n p r e s e n t s t r o u b l e s o m e p r o b l e m s . T r a n s p o r t of electricity in s e m i c o n d u c t o r s on t h e o t h e r h a n d is c o m p a r a t i v e l y simple; it t a k e s place a t r o o m t e m p e r a t u r e a n d is effected t h r o u g h t h e i n t e r m e d i a r y of a p - n j u n c t i o n . T h e speed of t h e m o t i o n of t h e free e l e c t r o n s in t h e t h e r m i o n i c v a l v e is large a n d b e c o m e s a l i m i t i n g factor o n l y a t frequencies of several h u n d r e d m e g a c y c l e s . Besides, t h e finite t i m e t a k e n b y t h e electrons for t h e i r p a s s a g e is a n a d v a n t a g e in c e r t a i n a p p l i c a t i o n s of specially d e s i g n e d t h e r m i o n i c valves. T h e p a s s a g e of electricity in a s e m i c o n d u c t o r , on t h e o t h e r h a n d , is b o u n d to be slow d u e to f r e q u e n t collisions w i t h t h e a t o m s of t h e m a t e r i a l . A f o r m u l a is given to define t h e speed of t h e p a s s a g e of electricity in s e m i c o n d u c t o r s s u c h as g e r m a n i u m . A n appreciable loss of g a i n is i n c u r r e d if e m p l o y e d a t f r e q u e n c i e s a b o v e 2 Mc./sec. T h e t r a n s i t t i m e is p r o p o r t i o n a l to t h e s q u a r e of t h e d i s t a n c e b e t w e e n e m i t t e r a n d collector a n d g r e a t t e c h n i c a l difficulties h a v e to be o v e r c o m e in o r d e r to r e d u c e t h i s d i s t a n c e to a v a l u e of t h e o r d e r of a few microns. A t t h a t distance, frequencies u p t o a few h u n d r e d m e g a c y c l e s m a y be e m p l o y e d b u t t h e r e is t h e c o n s t a n t d a n g e r of s h o r t circuiting collector a n d e m i t t e r . T h e effect of a n y p a r a s i t i c p h e n o m e n a w i t h i n a t h e r m i o n i c v a l v e c a n largely be c o m p e n s a t e d for, b u t in t h e case of t h e t r a n s i s t o r t h e whole m e c h a n i s m of o p e r a t i o n is n o t sufficiently explored to c o u n t e r a c t s u c h p h e n o m e n a b y a n y t h i n g b u t t e n t a t i v e m e a s u r e s . T h e p r o b l e m of noise is e q u a l l y u n s o l v e d . A l t h o u g h t h e r e is still m u c h w o r k to be carried o u t in o r d e r to m a k e t h e s e m i c o n d u c t o r a real rival to t h e t h e r m i o n i c v a l v e t h e fact s h o u l d n o t b e ignored t h a t t h e t r a n s i s t o r c a n be a p p l i e d w i t h a d v a n t a g e w h e r e a device of s m a l l d i m e n s i o n s a n d low c o n s u m p t i o n is required. Somma ire : L ' a u t e u r fait u n parall~le e n t r e le t u b e ~ vide et les s e m i - c o n d u c t e u r s , e x p o s a n t leurs a v a n t a g e s et l e u r s i n c o n v 6 n i e n t s respectifs.
Ab,tract No. and References
5s/iv
Article by J. Laplume Le V/de zo, March-April 1955 2-8
The Vacuum Obtainable in a Thermionic Valve and its Measurement See A b s t r a c t No.: 20/I
59/IV
Deterioration of Oxide Cathodes b y the Evolution of Gas from the Anode Under Electron Bombardment See A b s t r a c t No.: 19/I
6o/xv
Evaporation of Barium and Strontium from Oxide-Coated Cathodes United States. A n e x p e r i m e n t a l s t u d y is r e p o r t e d of t h e factors g o v e r n i n g t h e e v a p o r a t i o n , f r o m oxide c a t h o d e s , of b a r i u m , s t r o n t i u m a n d t h e i r c o m p o u n d s . T h e f a c t o r s s t u d i e d are: (1) O p e r a t i n g t e m p e r a t u r e , (2) s p a c e c u r r e n t d e n s i t y , (3) i m p u r i t i e s of t h e c a t h o d e core m a t e r i a l (nickel), (4) c o m p o s i t i o n of o t h e r electrodes. I n t h e m a i n series of e x p e r i m e n t s , a b o u t 400 triodes h a v i n g e s s e n t i a l l y t h e s t r u c t u r e of a r e p e a t e r v a l v e were a s s e m b l e d , p u m p e d a n d aged u n d e r identical conditions, b a t c h e s of 4 0 - 1 0 0 b e i n g s t u d i e d statistically. S a m p l e s of 3-15 v a l v e s were selected a t r a n d o m i m m e d i a t e l y a f t e r p u m p i n g , a n d a t i n t e r v a l s d u r i n g t h e ageing, for a n a l y s i s ; t h e grid a n d a n o d e were r e m o v e d f r o m e a c h valve, t h e m a t e r i a l collected on t h e m dissolved in h y d r o c h l o r i c acid a n d t h e s o l u t i o n s a n a l y s e d s p e c t r o c h e m i c a l l y b y t h e c o m p a r i s o n s t a n d a r d m e t h o d . T h e r e s u l t s g a v e t h e c u m u l a t i v e e v a p o r a t i o n w h i c h h a d occurred d u r i n g p u m p i n g a n d d u r i n g v a r i o u s periods of ageing, a n d were e x p r e s s e d in m i c r o g r a m p e r s q . c m , of c a t h o d e surface. T h e ageing c o n d i t i o n s were: F i l a m e n t t e m p e r a t u r e - - 1,02O°K, a n d a n o d e p o t e n t i a l - - 1 3 5 V g i v i n g a s p a c e c u r r e n t of 1 0 m A / c m . I. T h r e e t y p e s of nickel were u s e d as core m a t e r i a l for t h e filaments, t w o w i t h a b o u t 0 . 8 4 % i m p u r i t y , t h e t h i r d w i t h 0.03%. W i t h t h e l o w - p u r i t y s a m p l e s , a b o u t 50-80 ~g./sq.cm. w a s e v a p o r a t e d d u r i n g p u m p i n g , w h e n t h e f i l a m e n t w a s flashed a t 1,300°K for 2 m i n . T h e t o t a l increased to 110 ~g. a f t e r a b o u t 3,000 hr. ageing, followed b y a s t e a d y f u r t h e r increase of a b o u t 2 vg. p e r 1,000 hr. u p to 20,000 hr. (the l o n g e s t period quoted). T h e figures for t h e h i g h - p u r i t y nickel s h o w e d a b o u t 40 ~g. d u r i n g p u m p i n g a n d no significant increase d u r i n g ageing. I n all cases, s t r o n t i u m a c c o u n t e d for o n l y a b o u t 5 o of t h e t o t a l a n d it w a s concluded, from k n o w l e d g e of t h e v a p o u r p r e s s u r e s of B a O a n d SrO a t 1,300~K, t h a t v e r y little of either m e t a l could h a v e e v a p o r a t e d as oxide. T h i s conclusion, t h a t t h e p u r e m e t a l is involved, w a s c o n f i r m e d b y a second series of e x p e r i m e n t s in w h i c h t h e e v a p o r a t e d m a t e r i a l w a s cond e n s e d on a t u n g s t e n r i b b o n (the t e c h n i q u e of B e c k e r a n d Sears), t h e t h e r m i o n i c e m i s s i o n of w h i c h w a s t h e n o b s e r v e d , a n d b y o t h e r t e s t s in w h i c h t h e m a t e r i a l w a s allowed to r e a c t w i t h w a t e r v a p o u r , p r o d u c i n g h y d r o g e n . T e s t s w i t h o u t space c u r r e n t flow s h o w e d t h i s to h a v e a negligible effect on t h e e v a p o r a t i o n rate. T h e effect of f i l a m e n t t e m p e r a t u r e w a s t h a t a n increase of 80 ° to 1,100°K g a v e a four-fold increase in t h e t o t a l e v a p o r a t i o n of b a r i u m d u r i n g t h e first 4,000 hr. A factor n o t a t first s u s p e c t e d w a s t h e influence of a n o d e a n d grid m a t e r i a l (bright nickel in t h e first e x p e r i m e n t s ) . T h e u s e of cleaned a n d s u b s e q u e n t l y oxidised nickel a n o d e s a n d grids g r e a t l y r e d u c e d e v a p o r a t i o n , especially w i t h h i g h - p u r i t y nickel filaments, s u g g e s t i n g t h a t i m p u r i t i e s f r o m a n o d e and grid m a y h a v e c o n t r i b u t e d to t h e s u p p l y of excess b a r i u m in t h e c a t h o d e . I n fact, m a g n e s i u m w a s d e t e c t e d in t h e oxide c o a t i n g itself w h e n b r i g h t nickel a n o d e s were used, e v e n w i t h h i g h - p u r i t y nickel filaments. Cont r a r y to w h a t m i g h t h a v e b e e n e x p e c t e d , no correlation w a s f o u n d b e t w e e n t h e r m i o n i c e m i s s i o n a n d e v a p o r a t i o n . S o m m a i r e : L e s t a u x d ' ~ v a p o r a t i o n d u b a r i u m et d u s t r o n t i u m d u c a t h o d e s ~ o x y d e d ' u n t u b e c o u r a n t o n t 6t~ m e s u r 6 s p e n d a n t d e s essais d u dur~e jusqu'~. 20,000 h e u r e s .
01/IV
October, 1955
Vacuum Vol. V
Article by L. A. Wooten, A. E. Ruehle & G. E. l~oore J. AppL Phys. 26, Jan. 1955 44-51 327
VACUUM Classified Abstracts
Abstract No.
IV
and References
62/iv
Note by R. Levi J. Appl. Phys.
26, May 1955 639 & Le Vide
9, Nov. 1954 284-289 63/IV
--
Special
Subsidiary Contd.
Subjects
--
IV
Improved 'Impregnated C~thode' United States. Details are given of the properties of the new impregnated cathode which represents a development of the L-cathode. The same porous tungsten body of 3 ram, diameter as in the case of the L-cathode is used. The body is impregnated in a hydrogen atmosphere with a melt containing 5 moles of BaO, 2 moles of A l s o a and 3 moles of CaO. The L-cathode was impregnated in vacuum and the material consisted of 5 moles of BaO and 2 moles of A l t o s. The emission current density, measured pulsewise by discharging periodically across the diode an R-C network, having a time constant of 60 ~ see., at a repetition rate of 60 per see., has been increased four times. The ageing process required to obtain full and stable emission has been reduced from 3 days to 3 hr. The average total barium evaporation rate during the first 2,000 hr. of service life is reduced to 2 x l0 "~° g. of Ba per sq.cm, per sec. at 1,465°K. Life tests carried out at the same temperature exceeded 5,000 hr. without any failure. The operating characteristics of the new cathode when employed in a typical diode valve are shown in a graph. Sommaire: Des recherches faites auparavant dans le but d'am61iorer les techniques de fabrication de cathodes du type L ont cenduit au d~veloppement de 'cathodes impr6gn~es'.
The Evolution of Particle Counters Switzerland. Counting devices necessary for assaying the rate of emission of particles have become of general
Article by H. Oreinacher Endeavour
I3, Oct. 1954 190-197 64/IV
scientific importance. The evolution of counters is surveyed and the principle characteristics of types at present in use are reviewed. Elster and Geitel discovered in 1903 t h a t m-particles striking zinc blende (ZnS) produce light flashes. This device was employed for the detection and counting of "-particles until Rutherford and Geiger in 1908 developed an improved method for the detection and counting of "-particles by means of their ionising action. This led to the first design of the proportional (gas multiplication) counter. Details of the operating principle of the counter are given. The method ranges today among the fastest available: 1,000,000 a second can be counted. I t facilitates the counting of =-particles independently of any ~-particles since the latter have about 100 times weaker an ionising power. Geiger developed in 1913 t b e p o i n t counter. The output of this instrument is proportional to the primary ionisation and facilitates the counting of ~- ~- and 7-particles. An instrument which facilitated the measurement of the ionisation produced by single ,,-particles and protons was developed by Kohlrausch and Schweidler in 1912, known as the electrometer counter. However its counting is slqw and therefore the method is not generally applied. In 1924 the author of the present article developed the so-called chamber counter which facilitates the detection of particles directly through their primary ionisation. The chamber counter facilitates counting of "-particles and protons without interference from ~- and 7-particles present at the same time. Up to 1928 the counter had to be used for the counting of 6- and 7-rays. In t h a t year Geiger and Miiller published the improved design of a counter, known today as the GeigerMiiller counter, which was a development of the multiplication counter. This design was improved in 1935 by Trost, by providing a 'self-quenching' effect. The author proceeds to describe the hydraulic design of a spark counter and later developments of this instrument. Methods of counting based on the action of electron multipliers were brought into practical use in 1936 by Zworykin and represent a major deviation from the operating principle employed on previous counters, i.e. from counting methods based on gas ionisation. The article concludes with a description of the scintillation counter originated by Kallmann in 1947. Crystals and liquids which show changes of resistance when particles are incident upon them can also form the basis of counters. Sommaire: On passe en revue l'~volution des compteurs et les caract6ristiques principales de quelques types actuels.
Techniques for Counting Radiokrypton See Abstract No.: 5/IV
65/IV
~2s
Radiocarbon Dating System See Abstract No.: 139/III
Vacuum Tr ^ 7
¥7
Oaober 1955
VACUUM Classified Abstracts
Author Index, Author
Vol. V
(I955)
Title of Publication
Aitken, P. B., et al. Alexander, J., et al. Alexeff, I., et al. Allegheny Ludlum Steel Corp., et al. Allen, F. G., et al. Allen, T. K., et al. Alvarez, L. W . , et al. Andersson, L., et al. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon. Anon (A.S.H.). Armour & Co., et al. Atkins, D. F., et al.
New Design of a Vacuum Jacket Precision Combustion Calorimeter. Twenty-Stage Molecular Distillation Unit. Evapor-Ion P u m p Developments. Wrapped Alloy Core Electrode.
Bach, B. B., et al. Bailey, R. A., et al. Bailleuil-Langlais, J. Ballentine, O. M.
Hydrogen in Cast Iron. The Appearance of Some Oscillating Discharges. The Vacuum Obtainable in a Thermionic Valve and Its Measurement. Procedure for Determining Vapour Pressures of Materials of Low Volatility. Use of the Gliding Spark for Spectro Analysis in the Far Ultra-Violet. Improvements r.t. Rotary Vacuum Pumps. Production of Hafnium. High Vacuum Metallising and Toy Manufacture. Gassing of Liquid Dielectrics Under Electrical Stress. How Processing Conditions Affect Micro-Organism Radio-Resistance. Metal-Film Resistance Thermometers for Measuring Surface Temperatures. A Study of Consumable Electrode Arc Melting. Production of Zirconium Alloys by Consumable Electrode Arc Melting. The Magnetically Suspended Equilibrium Ultracentrifuge. Ultra High Vacua. Carbonyl Process.
Balloffet, G., et al. Bancroft, F. E., et al. Barr, M. M., et al. Barrett, A. S. D. Basseches, H., et al. Bates, C. J., et aL Baus, B. V., et al. Beall, R. A., et al. Beall, R. A., et al. Beams, J. w . , a al. Becker, J. A. Bell Telephone Labs. Inc., et aL Bell Telephone Labs. Inc., et al. Bendersky, D. Benner, F. C., et al. Berkeley, F. D. Berkowitz, A. E.
Bernier, J. P.,
et al.
Bernier, J. c., et al. Berry, R . , et al.
October, 1955
Abstr. No. 107/I 132/III 4/II 95/III
Ultra-High Vacuum Valve. 98/II The Appearance of Some Oscillating Discharges. 60/I Berkeley Proton Linear Accelerator. 35/IV Freeze-Drying with a Modified Glick-Malmstrom Apparatus. 30/IV Metallic Coatings on Non-Metallic Materials. IV. Vacuum Coating Methods 4 / I I I Ceramic Twin-Triode Pumping Technique. 23/II Medical Research Council's Cyclotron. 39/IV Evaporated Films--New Use? 44/I The Electron Microscope and Some of Its Industrial Applications. 61/II Finishing Ever Ready Lamps. 71/I Vacuum Brazed Clad Metal Now Commercial Reality. 82/I Applying Test Loads by Vacuum. 84/I Seal-Off Valve for Vacuum Systems. 102/II Vacuum Melting Furnace Installation a t Carboloy Plant. 107/III Vacuum Bushings. 109/II Vacuum Annealing Upgrades Metals ll0/III Precision Casting with Vacuum and I n e r t Gases. ll9/III A Modern Cryogenic Engineering Laboratory. 145/I Good Tomato Powder Made Experimentally. 152/III Giant Chambers Cool Lettuce. 154/III Buhler Vacuum Paste-Goods Device. 156/III Stainless Provides Durability in De-aerators. 158/III 3 Keys to Clear Solution. 160/I Vacuum Flotation for Coal Fines. 160/III Melt Quality Tests. I. Non-Ferrous. 190/I Titanium and Zirconium Tubing Annealed in Vacuum Furnace. 201/I A Metallurgical Study of Molybdenum. Quarterly Status Report. 210/I Aluminised Clothing to Give Heat the Bounce. 216/I TV Chemicals. 55/I Improvements i.o.r.t. Closures for Lyophilisation Containers. 31/IV Electronic Vacuum Dilatometer. 53/II
Electrical Capacitors.
81/1I 60/1
20/I llS/II 651I 20/II 2071I 45/I 12/I 151/I ll0/I 94/III 99/III 55/II 8/I 123/III 48/III
A Special Thermocouple for Measuring Transient Temperatures. Improvements i.o.r.t, the Coating of Threads With Metals. Air Ejectors Cheaper T h a n Steam. Relation to Diffusion Measurements of Some Beta-Ray Absorption Phenomena. A Direct Measurement of the Energy Locally Absorbed from a GammaRay Beam. High Vacuum Pump. Improvements i.o.r.t. Valves. Vacuum Vol. V
75/I 215/I 22/II 97/I 96/I 12/II I01/II
329