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A sensitive differential manometer
VACUUM Classified A b s t r a c t s
II ---
Vacuum Apparatus and Auxiliaries Contd.
--
II
Abstract No. and References
The p u m p i n g action of these gauges for oxygen has been investigated. The expected rate of oxygen adsorption has been calculated to be 0.26 litres/second. This is r o u g h l y confirmed b y e x p e r i m e n t . . The p u m p i n g of v a p o u r s and gases originating f r o m t h e diffusion p u m p is based on a s o m e w h a t different m e c h a n i s m from t h a t a s s u m e d for the cold-cathode ionisation gauge. I t h a s been stated previously t h a t no p u m p i n g effect could be observed w h e n the glass envelope of t h e gauge was operated at a t e m p e r a t u r e above 200°C, whilst the collector was r u n n i n g at a t e m p e r a t u r e of 280°C. I t can be a s s u m e d therefore t h a t the glass envelope is the actual sorbing surface, i 2 , the oil decomposition p r o d u c t s dissociate u p o n collision w i t h the hot filament and are sorbed b y the s u r r o u n d i n g cooler surfaces. The influence of the gauge t u b u l a t i o n on the pressure reading of the ins t r u m e n t is d e m o n s t r a t e d in a table. Sommaire : La sensibilit6 de la jauge ~ ionisation ~ cathode chaude a 6td etudi6e et les diffdrents aspects de son effet de p o m p a g e a u x tr~s basses pressions examin6s.
Article by L. Riddiford J. Sci. Instrum. 28, Dec. 1951 375-379
On the Application of a Philips Ionisation Gauge Type of Ion Source in a Mass Spectrometer Leak Detector
13/II
See _~:bstract No. : 4 1 / I I
O
Electronic Manometer Measures Minute Pressures United States. Tile m i c r o m a n o m e t e r referred to was constructed for use with a m a s s spectrometer and gives direct readings of pressure on a scale t h a t can be calibrated in units of pressure. ( B . S . I . t ~ . A . Bulletin) Sommaire : Description d ' u n m i c r o m a n o m 6 t r e destin~ "t ~tre employd avec le spectrom~tre de masse,
Knudsen Gauges United Kingdom.
Note by Anon. Math. Design 23, Aug. 1951 119
15/I1
A brief revieCv of the development and applications of the K n u d s e n gauge is followed b y a detailed description of i m p r o v e d forms of metal and glass gauges. Their performance w i t h respect to factors such as outgassing, m e t h o d s of suspension, extension of range b y electro-magnetic compensation, and d a m p i n g are discussed. The t h e o r y of the absolute m a n o m e t e r is reviewed. I n particular, t h e f u n d a m e n t a l a s s u m p t i o n s concerning a c c o m m o d a t i o n coefficient, the edge effect due to large heater-to-vane distance, a n d v a n e t e m p e r ature in t h e low pressure (Knudsen) region are discussed. A t h e o r y is developed to give a correction factor for a rectangular vane a n d h e a t e r valid for a n y dimensions and distance. I t is s h o w n t h a t u n d e r certain conditions calibration is independent of the t e m p e r a t u r e of the vane. Sommaire : Bref c o m p t e r e n d u sur le ddveloppement et les application~ de la jauge de Knudsen, suivi de la description ddtaill~e de formes amdliorSes de jauges m~talliques et en verre.
A New All-Glass Membrane Manometer United Kingdom. I n pressure m e a s u r e m e n t s involving substances which m i g h t a t t a c k m e r c u r y all-glass
O
14/II
m a n o m e t e r s are p a r t i c u l a r l y useful. The a u t h o r s refer in particular to m a n o m e t e r s of the d i a p h r a g m type, where the corrosive gas, the pressure of which is to be measured, is kept on one side of the d i a p h r a g m and a m e r c u r y m a n o m e t e r is connected to the s y s t e m on the other side of tim d m p h r a g m . Details are given of a n e w design developed b y the authors. The d i a p h r a g m of the n e w m a n o m e t e r is in contact with a vertical lever, which consists of a glass t u b e and contains a p l a t i n u m wire, suspended f r o m a glass spring. The zero position is checked b y electrical c o n t a c t with the p l a t i n u m wire. The d i a p h r a g m has a d i a m e t e r of a b o u t 2 cm. and is kept as t h i n as possible. This gauge has been used with success for the m e a s u r e m e n t of the v a p o u r pressures of stannic halides in t h e t e m p e r a t u r e range 20-340°C. Tile gauge facilitates readings with a precision of 0.1 m m . Hg. T h e variation of the zero setting is less irregular t h a n is the case with o t h e r gauges of this type. I t should be useful in all instances, where the measuring procedure requires successive heating and cooling of the gauge. S o m m a i r e : On donne les d~tails d ' u n m a n o m ~ t r e ~ m e m b r a n e enti~rement en verre employ6 avec succ6s p o u r le m e s u r a g e de la pression de v a p e u r des halog~nures s t a n n i q u e s en t e m p 6 r a t u r e s v a r i a n t de la t e m p 6 r a t u r e a t m o s p h 6 r i q u e j u s q u ' h e n v i r o n 340°C,
A Sensitive Differential Manometer Canada. A description is given of a differential m a n o m e t e r of small volume, developed b y the a u t h o r for a
Article by W. Steckelmacher Vacuum x, Oct. 1951 266-282 16/II
Note by A. Kabesh & R. S. Nyholm J. Chem. Soe. Nov, 19~1
3252-3253 17/II
special purpose. I t is capable of a precision of 0.1 to 0.2 micron Hg. The i n s t r u m e n t consists of two m e a s u r i n g cells each connected to nearly identical oscillator circuits and is of the d i a p h r a g m gauge type, where t h e d i a p h r a g m is one plate of a n electrical condenser. I n this case the m e r c u r y surface serves as t h e diaphragm. F o r m o s t m e a s u r e m e n t s t h e distance b e t w e e n condenser plate and m e r c u r y surface in each of the two cells was held a t 1.3 m m . B o t h m e a s u r i n g cells were m o u n t e d on a brass plate which in t u r n was bolted to a concrete base, r e s t i n g on shock absorbers. Vibration w a s n o t eliminated altogether, b u t reduced to a n a m o u n t which did n o t interfere w i t h the m e a s u r e m e n t s . Changes in t e m p e r a t u r e h a d some effect on t h e position of the m e r c u r y levels a n d h a d to be t a k e n into a c c o u n t w h e n o p e r a t i n g the i n s t r u m e n t . A wire sealed into t h e b o t t o m of t h e m a n o m e t e r connected t h e t o t a l m a s s of m e r c u r y to t h e g r o u n d a n d t h u s acted as a r e t u r n lead
J a n u a r y , 1952
vacuum Vol. I I No. I
78
VACUUM Classified Abstracts
II
Vacuum Apparatus and Auxiliaries --
II
Contd.
to the oscillators. A change of p r e s s u r e changed the capacity in the t w o oscillator circuits in opposite directions. The beat frequency of t h e oscillator was c o m p a r e d on a n oscilloscope w i t h t h e o u t p u t of a n audio-signal generator with a v e r y high f r e q u e n c y stability in t h e range of 1,000 to 100,000 cycles/second. Details are given of t h e electrical circuit. A m a t h e m a t i c a l analysis of t h e o p e r a t i o n of the i n s t r u m e n t is added. The m a n o m e t e r m a y be used for highly accurate m e a s u r e m e n t s over a small p r e s s u r e range or for less accurate measurem e n t s over a wide pressure range. Sommaire : Description d ' u n m a n o m 6 t r e diffdrentiel au m e r c u r e de construction spdciale.
Determination of Mercury Level in a Steel-Tube Manometer United K i n g d o m . A device for reading t h e m e r c u r y level in a steel-tube m a n o m e t e r is described which
O
consists of a radiation source e m i t t i n g a b e a m of g a m m a r a y s which p e n e t r a t e s the steel-tube of the m a n o m e t e r and enters into a n ionisation c h a m b e r detector on t h e opposite side. The ionisation c u r r e n t passes t h r o u g h a resistance connected to the grid circuit of t h e electrometer valve, t h e o u t p u t of which is amplified and fed to the Yl-plate of a cathode r a y tube. The p o t e n t i a l of this plate is t h u s p r o p o r t i o n a l to the intensity of the radiation reaching the chamber. W h e n t h e radiation passes t h r o u g h t h e m e r c u r y column the ionisation c u r r e n t is low, b u t if the m e r c u r y h a s n o t reached the level of t h e radiation p a t h t h e ionisation c u r r e n t is high. I n t e r m e d i a t e values occur, where the n a r r o w b e a m passes t h r o u g h the meniscus of the mercury, the exact value being determined b y the p r o p o r t i o n of m e r c u r y and air included in the beam. The r a d i u m source is m o u n t e d in a lead p o t giving protection in all directions except on a line ~arough t h e m a n o m e t e r tube. The l a t t e r is screened b y the ionisation c h a m b e r itself. Details of the design a~e discussed and an electrical circuit d i a g r a m is shown. Sommaire: Description d ' u n dispositif p a r lequel la h a u t e u r de la colonne de mercure dans un t u b e en acier p e u t ~tre ddtermin6e. I1 consiste en une source radiactive c o m a e 6mitteur et une c h a m b r e k ionisation c o m a e r~cepteur.
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MEASURING
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in o r d i n a r y d y n a m i c v a c u u m systems. Two different t y p e s of m a s s spectrometers were used for the experiments. One of the t u b e s was constructed t h r o u g h o u t f r o m silica glass and copper and was entirely free f r o m d e m o u n t a b l e joints, the o t h e r was m a d e of b r a s s or stainless steel and was fitted with r u b b e r gaskets. The former t y p e was evacuated b y m e r c u r y diffusion p u m p s , t h e latter b y oil diffusion p u m p s . E x a m i n i n g the conditions during t~he initial evacuation period it was found t h a t the o x y g e n p r e s s u r e was less t h a n 10-~mm, H g after 20 m i n u t e s of p u m p i n g and less t h a n 10-Smm. H g after one h o u r of p u m p i n g . 70% of t h e ions p r e s e n t were formed f r o m w a t e r and m o s t of t h e r e m a i n d e r from h y d r o c a r b o n vapours. The c a r b o n m o n o x i d e concentration was a b o u t 3% of that of the water. The conclusion is t h a t in the early stages of an evacuation process the concentrations of all kinds of molecules diminish at a p p r o x i m a t e l y the same rate. I n a n o t h e r series of e x p e r i m e n t s t h e effects of low t e m p e r a t u r e b a k i n g h a v e been investigated. After stabilising t h e residual pressure the s y s t e m was baked a t 100°C for a period of 4 h o u r s and the t e m p e r a t u r e of the cold t r a p maintained a t - 78°C. This e x p e r i m e n t p r o v e d t h a t w a t e r c a n n o t effectively be r e m o v e d in these conditions. I t is m e r e l y transferred to the cold surface from which it re-evaporates, a typical c a s e of a ' v i r t u a l leak '. Analysing the residual gases prevailing at e x t r e m e l y low pressures it was found t h a t constructional m e t h o d s and p u m p fluids h a d v e r y little influence on the composition of the gases unless high t e m p e r a t u r e b a k i n g was employed. I n all t r a p p e d s y s t e m s the m o r e a b u n d a n t residual was water. The residual h y d r o c a r b o n pressure was higher in s y s t e m s served b y oil diffusion p u m p s t h a n in those served b y m e r c u r y p u m p s b u t t h e difference was n o t v e r y marked. The presence of h y d r o c a r b o n molecules in s y s t e m s evacuated b y m e r c u r y diffusion p u m p s even if p r o p e r l y baked and t r a p p e d can be explained as follows : I n the intitial stage of evacuation, the diffusion p u m p c a n n o t be switched on for fear of oxidation and the cold t r a p c a n n o t be cooled because this would cause condensation of large q u a n t i t i e s of water. A t this stage oil molecules from the r o t a r y p u m p diffuse t h r o u g h o u t t h e s y s t e m and some of t h e m are a b s o r b e d on t h e fine side. E v e n prolonged high t e m p e r a t u r e baking and the application of cold t r a p s at the t e m p e r a t u r e of liquid nitrogen seldom succeeds in r e m o v i n g these molecules completely. I t a p p e a r s advisable, therefore, to place a n active c a r b o n t r a p between the r o t a r y and diffusion p u m p if v e r y low pressures are to be obtained,
Sommaire : Le spectrom+tre de masse a 6t6 utilisd p o u r l'6tude de la n a t u r e et le c o m p o r t e m e n t de gaz r6siduels dans u n syst6me n o r m a l d y n a m i q u e ~t vide.
A Cold-Cathode Mass Spectrometer Leak Detector
Arbicle by J. M. Los & J. A. Morrison Rev. Sci. Instrum. 2z, Nov. 1951 805-809
18/II
Article by R. Meakin J Set. Instru~. z8, Dec. 1951 372-373
zz
Application of the Mass Spectrometer to High Vacuum Problems United K i n g d o m . Details are given of an investigation into the composition a n d behaviour of residual gases
O
Abstract No. and References
19/1i
Article by J. Blears J. Sci. Instrum. Suppl. 1, 1951 36-42
~,o/Ii
See A b s t r a c t No. : 4 0 / I I
J a n u a r y , 1952
vowuum VoL I I No. I
79
II ---
Vacuum Apparatus and Auxiliaries Contd.
--
II
Abstract No. and References
The p u m p i n g action of these gauges for oxygen has been investigated. The expected rate of oxygen adsorption has been calculated to be 0.26 litres/second. This is r o u g h l y confirmed b y e x p e r i m e n t . . The p u m p i n g of v a p o u r s and gases originating f r o m t h e diffusion p u m p is based on a s o m e w h a t different m e c h a n i s m from t h a t a s s u m e d for the cold-cathode ionisation gauge. I t h a s been stated previously t h a t no p u m p i n g effect could be observed w h e n the glass envelope of t h e gauge was operated at a t e m p e r a t u r e above 200°C, whilst the collector was r u n n i n g at a t e m p e r a t u r e of 280°C. I t can be a s s u m e d therefore t h a t the glass envelope is the actual sorbing surface, i 2 , the oil decomposition p r o d u c t s dissociate u p o n collision w i t h the hot filament and are sorbed b y the s u r r o u n d i n g cooler surfaces. The influence of the gauge t u b u l a t i o n on the pressure reading of the ins t r u m e n t is d e m o n s t r a t e d in a table. Sommaire : La sensibilit6 de la jauge ~ ionisation ~ cathode chaude a 6td etudi6e et les diffdrents aspects de son effet de p o m p a g e a u x tr~s basses pressions examin6s.
Article by L. Riddiford J. Sci. Instrum. 28, Dec. 1951 375-379
On the Application of a Philips Ionisation Gauge Type of Ion Source in a Mass Spectrometer Leak Detector
13/II
See _~:bstract No. : 4 1 / I I
O
Electronic Manometer Measures Minute Pressures United States. Tile m i c r o m a n o m e t e r referred to was constructed for use with a m a s s spectrometer and gives direct readings of pressure on a scale t h a t can be calibrated in units of pressure. ( B . S . I . t ~ . A . Bulletin) Sommaire : Description d ' u n m i c r o m a n o m 6 t r e destin~ "t ~tre employd avec le spectrom~tre de masse,
Knudsen Gauges United Kingdom.
Note by Anon. Math. Design 23, Aug. 1951 119
15/I1
A brief revieCv of the development and applications of the K n u d s e n gauge is followed b y a detailed description of i m p r o v e d forms of metal and glass gauges. Their performance w i t h respect to factors such as outgassing, m e t h o d s of suspension, extension of range b y electro-magnetic compensation, and d a m p i n g are discussed. The t h e o r y of the absolute m a n o m e t e r is reviewed. I n particular, t h e f u n d a m e n t a l a s s u m p t i o n s concerning a c c o m m o d a t i o n coefficient, the edge effect due to large heater-to-vane distance, a n d v a n e t e m p e r ature in t h e low pressure (Knudsen) region are discussed. A t h e o r y is developed to give a correction factor for a rectangular vane a n d h e a t e r valid for a n y dimensions and distance. I t is s h o w n t h a t u n d e r certain conditions calibration is independent of the t e m p e r a t u r e of the vane. Sommaire : Bref c o m p t e r e n d u sur le ddveloppement et les application~ de la jauge de Knudsen, suivi de la description ddtaill~e de formes amdliorSes de jauges m~talliques et en verre.
A New All-Glass Membrane Manometer United Kingdom. I n pressure m e a s u r e m e n t s involving substances which m i g h t a t t a c k m e r c u r y all-glass
O
14/II
m a n o m e t e r s are p a r t i c u l a r l y useful. The a u t h o r s refer in particular to m a n o m e t e r s of the d i a p h r a g m type, where the corrosive gas, the pressure of which is to be measured, is kept on one side of the d i a p h r a g m and a m e r c u r y m a n o m e t e r is connected to the s y s t e m on the other side of tim d m p h r a g m . Details are given of a n e w design developed b y the authors. The d i a p h r a g m of the n e w m a n o m e t e r is in contact with a vertical lever, which consists of a glass t u b e and contains a p l a t i n u m wire, suspended f r o m a glass spring. The zero position is checked b y electrical c o n t a c t with the p l a t i n u m wire. The d i a p h r a g m has a d i a m e t e r of a b o u t 2 cm. and is kept as t h i n as possible. This gauge has been used with success for the m e a s u r e m e n t of the v a p o u r pressures of stannic halides in t h e t e m p e r a t u r e range 20-340°C. Tile gauge facilitates readings with a precision of 0.1 m m . Hg. T h e variation of the zero setting is less irregular t h a n is the case with o t h e r gauges of this type. I t should be useful in all instances, where the measuring procedure requires successive heating and cooling of the gauge. S o m m a i r e : On donne les d~tails d ' u n m a n o m ~ t r e ~ m e m b r a n e enti~rement en verre employ6 avec succ6s p o u r le m e s u r a g e de la pression de v a p e u r des halog~nures s t a n n i q u e s en t e m p 6 r a t u r e s v a r i a n t de la t e m p 6 r a t u r e a t m o s p h 6 r i q u e j u s q u ' h e n v i r o n 340°C,
A Sensitive Differential Manometer Canada. A description is given of a differential m a n o m e t e r of small volume, developed b y the a u t h o r for a
Article by W. Steckelmacher Vacuum x, Oct. 1951 266-282 16/II
Note by A. Kabesh & R. S. Nyholm J. Chem. Soe. Nov, 19~1
3252-3253 17/II
special purpose. I t is capable of a precision of 0.1 to 0.2 micron Hg. The i n s t r u m e n t consists of two m e a s u r i n g cells each connected to nearly identical oscillator circuits and is of the d i a p h r a g m gauge type, where t h e d i a p h r a g m is one plate of a n electrical condenser. I n this case the m e r c u r y surface serves as t h e diaphragm. F o r m o s t m e a s u r e m e n t s t h e distance b e t w e e n condenser plate and m e r c u r y surface in each of the two cells was held a t 1.3 m m . B o t h m e a s u r i n g cells were m o u n t e d on a brass plate which in t u r n was bolted to a concrete base, r e s t i n g on shock absorbers. Vibration w a s n o t eliminated altogether, b u t reduced to a n a m o u n t which did n o t interfere w i t h the m e a s u r e m e n t s . Changes in t e m p e r a t u r e h a d some effect on t h e position of the m e r c u r y levels a n d h a d to be t a k e n into a c c o u n t w h e n o p e r a t i n g the i n s t r u m e n t . A wire sealed into t h e b o t t o m of t h e m a n o m e t e r connected t h e t o t a l m a s s of m e r c u r y to t h e g r o u n d a n d t h u s acted as a r e t u r n lead
J a n u a r y , 1952
vacuum Vol. I I No. I
78
VACUUM Classified Abstracts
II
Vacuum Apparatus and Auxiliaries --
II
Contd.
to the oscillators. A change of p r e s s u r e changed the capacity in the t w o oscillator circuits in opposite directions. The beat frequency of t h e oscillator was c o m p a r e d on a n oscilloscope w i t h t h e o u t p u t of a n audio-signal generator with a v e r y high f r e q u e n c y stability in t h e range of 1,000 to 100,000 cycles/second. Details are given of t h e electrical circuit. A m a t h e m a t i c a l analysis of t h e o p e r a t i o n of the i n s t r u m e n t is added. The m a n o m e t e r m a y be used for highly accurate m e a s u r e m e n t s over a small p r e s s u r e range or for less accurate measurem e n t s over a wide pressure range. Sommaire : Description d ' u n m a n o m 6 t r e diffdrentiel au m e r c u r e de construction spdciale.
Determination of Mercury Level in a Steel-Tube Manometer United K i n g d o m . A device for reading t h e m e r c u r y level in a steel-tube m a n o m e t e r is described which
O
consists of a radiation source e m i t t i n g a b e a m of g a m m a r a y s which p e n e t r a t e s the steel-tube of the m a n o m e t e r and enters into a n ionisation c h a m b e r detector on t h e opposite side. The ionisation c u r r e n t passes t h r o u g h a resistance connected to the grid circuit of t h e electrometer valve, t h e o u t p u t of which is amplified and fed to the Yl-plate of a cathode r a y tube. The p o t e n t i a l of this plate is t h u s p r o p o r t i o n a l to the intensity of the radiation reaching the chamber. W h e n t h e radiation passes t h r o u g h t h e m e r c u r y column the ionisation c u r r e n t is low, b u t if the m e r c u r y h a s n o t reached the level of t h e radiation p a t h t h e ionisation c u r r e n t is high. I n t e r m e d i a t e values occur, where the n a r r o w b e a m passes t h r o u g h the meniscus of the mercury, the exact value being determined b y the p r o p o r t i o n of m e r c u r y and air included in the beam. The r a d i u m source is m o u n t e d in a lead p o t giving protection in all directions except on a line ~arough t h e m a n o m e t e r tube. The l a t t e r is screened b y the ionisation c h a m b e r itself. Details of the design a~e discussed and an electrical circuit d i a g r a m is shown. Sommaire: Description d ' u n dispositif p a r lequel la h a u t e u r de la colonne de mercure dans un t u b e en acier p e u t ~tre ddtermin6e. I1 consiste en une source radiactive c o m a e 6mitteur et une c h a m b r e k ionisation c o m a e r~cepteur.
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(VACUUM)
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in o r d i n a r y d y n a m i c v a c u u m systems. Two different t y p e s of m a s s spectrometers were used for the experiments. One of the t u b e s was constructed t h r o u g h o u t f r o m silica glass and copper and was entirely free f r o m d e m o u n t a b l e joints, the o t h e r was m a d e of b r a s s or stainless steel and was fitted with r u b b e r gaskets. The former t y p e was evacuated b y m e r c u r y diffusion p u m p s , t h e latter b y oil diffusion p u m p s . E x a m i n i n g the conditions during t~he initial evacuation period it was found t h a t the o x y g e n p r e s s u r e was less t h a n 10-~mm, H g after 20 m i n u t e s of p u m p i n g and less t h a n 10-Smm. H g after one h o u r of p u m p i n g . 70% of t h e ions p r e s e n t were formed f r o m w a t e r and m o s t of t h e r e m a i n d e r from h y d r o c a r b o n vapours. The c a r b o n m o n o x i d e concentration was a b o u t 3% of that of the water. The conclusion is t h a t in the early stages of an evacuation process the concentrations of all kinds of molecules diminish at a p p r o x i m a t e l y the same rate. I n a n o t h e r series of e x p e r i m e n t s t h e effects of low t e m p e r a t u r e b a k i n g h a v e been investigated. After stabilising t h e residual pressure the s y s t e m was baked a t 100°C for a period of 4 h o u r s and the t e m p e r a t u r e of the cold t r a p maintained a t - 78°C. This e x p e r i m e n t p r o v e d t h a t w a t e r c a n n o t effectively be r e m o v e d in these conditions. I t is m e r e l y transferred to the cold surface from which it re-evaporates, a typical c a s e of a ' v i r t u a l leak '. Analysing the residual gases prevailing at e x t r e m e l y low pressures it was found t h a t constructional m e t h o d s and p u m p fluids h a d v e r y little influence on the composition of the gases unless high t e m p e r a t u r e b a k i n g was employed. I n all t r a p p e d s y s t e m s the m o r e a b u n d a n t residual was water. The residual h y d r o c a r b o n pressure was higher in s y s t e m s served b y oil diffusion p u m p s t h a n in those served b y m e r c u r y p u m p s b u t t h e difference was n o t v e r y marked. The presence of h y d r o c a r b o n molecules in s y s t e m s evacuated b y m e r c u r y diffusion p u m p s even if p r o p e r l y baked and t r a p p e d can be explained as follows : I n the intitial stage of evacuation, the diffusion p u m p c a n n o t be switched on for fear of oxidation and the cold t r a p c a n n o t be cooled because this would cause condensation of large q u a n t i t i e s of water. A t this stage oil molecules from the r o t a r y p u m p diffuse t h r o u g h o u t t h e s y s t e m and some of t h e m are a b s o r b e d on t h e fine side. E v e n prolonged high t e m p e r a t u r e baking and the application of cold t r a p s at the t e m p e r a t u r e of liquid nitrogen seldom succeeds in r e m o v i n g these molecules completely. I t a p p e a r s advisable, therefore, to place a n active c a r b o n t r a p between the r o t a r y and diffusion p u m p if v e r y low pressures are to be obtained,
Sommaire : Le spectrom+tre de masse a 6t6 utilisd p o u r l'6tude de la n a t u r e et le c o m p o r t e m e n t de gaz r6siduels dans u n syst6me n o r m a l d y n a m i q u e ~t vide.
A Cold-Cathode Mass Spectrometer Leak Detector
Arbicle by J. M. Los & J. A. Morrison Rev. Sci. Instrum. 2z, Nov. 1951 805-809
18/II
Article by R. Meakin J Set. Instru~. z8, Dec. 1951 372-373
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Application of the Mass Spectrometer to High Vacuum Problems United K i n g d o m . Details are given of an investigation into the composition a n d behaviour of residual gases
O
Abstract No. and References
19/1i
Article by J. Blears J. Sci. Instrum. Suppl. 1, 1951 36-42
~,o/Ii
See A b s t r a c t No. : 4 0 / I I
J a n u a r y , 1952
vowuum VoL I I No. I
79