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Penning gauge as leak detector
VACUUM Classified A b s t r a c t s
II
-
-
Vacuum
Apparatus
and Auxiliaries
--
II
Contd.
Penning Gauge as Leak Detector Yugoslavia. A modified probe gas technique for cold ionisation gauges of a n y t y p e is described which facilitates s i m u l t a n e o u s pressure m e a s u r e m e n t and leak detection b y the aid of the p o t e n t i o m e t e r method. The m e t h o d is simple, accurate and reliable over a large pressure range. The gauge used in the experiments described h a d an anode ring of m o l y b d e n u m 0.6 cm. long with internal diameter 2 cm., and t w o stainless steel cathode plates 1.5 cm. in diameter and 2.5 cm. apart. The applied anode voltage was 900 V and the magnetic field s t r e n g t h 400 G. The working range was 5 × 10 -8 to 5 × 10 -8 ram. Hg. The circuit included a galvanometer G (sensitivity 3 × 10 "g A./mm.) in series w i t h the gauge. The potential difference across G was balanced b y a cell and variable resistances. Using H , and CO 8 as probe gases, changes of pressure of ca. 10 -8 m m . H g could be detected. Use of CO, caused the discharge c u r r e n t to decrease with time, due p r o b a b l y to formation of c a r b o n a t e film on the electrodes. Using H 2, leak detection was possible over the working range of the gauge.
Beta Gauge for Localised Measurements on Thin Films United States. A device is described which allows non-destructive p o i n t - b y - p o i n t thickness m e a s u r e m e n t of films used as cyclotron targets. The film is m o u n t e d on a microscope-type moveable stage over a collimated b e t a source, a t h i n - w i n d o w Geiger t u b e being fixed above it. The source was prepared b y depositing a b o u t 5 mC of carrier-free p r o m e t h i u m chloride in a circle of a b o u t 0.05 inch diameter on a disc of 0.04 inch thick Lucite plastic. The collimator is m a d e of { inch thick Lucite with a ~ inch hole t h r o u g h it. s u r m o u n t e d b y a inch thick lead washer. The b e a m is a b o u t ~ inch in diameter and thickness variations of less t h a n 0.1 mg./sq, cm. (alumininm equivalent) can be measured for thicknesses up to a b o u t 6 mg./sq.cm. Properties of Evaporated Metal Films Related to Their Use for Surface Temperature Measurements United States. The use of e v a p o r a t e d metal films as resistance t h e r m o m e t e r s for surface t e m p e r a t u r e measurem e n t s is described. The properties of thin films of the m o s t chemically inert and refractory, metals h a v e been studied so t h a t stable resistance t h e r m o m e t e r s can be obtained. W i t h films 300-3,000 A thick, accuracies of 0.01°C have been obtained for useful periods of time. The a d v a n t a g e s of thin films in this application a r e : - (i) L o w t h e r m a l capacity of the element. (if) Simple resistance m e a s u r e m e n t (iii) Surface t o p o g r a p h y is unchanged. The useful t e m p e r a t u r e range is from r o o m t e m p e r a t u r e up to a b o u t 300°C for Co, Cr, Ni and P t films. The m e t h o d s of p r e p a r a t i o n include the use of resistance heated v a p o u r sources and also sources heated b y electron b o m b a r d m e n t a t 4 kV and "up to 0.5A. A large n u m b e r of trial r u n s were carried out to establish a s t a n d a r d technique of m a n u f a c t u r e and use of the films. The mechanical and chemical resistance were c o m p a r e d for different metals b y m e a n s of abrasion t e s t s and etching tests. I n general, the thin films were found to have a greater chemical resistance t h a n the bulk metals. The films were aged artificially b y heating at least to the t e m p e r a t u r e of operation, and this is discussed fully in relation to the m e t h o d of film preparation. G r a p h s h a v e been plotted which s h o w the relationship between the resistivity of film and of bulk metal, and the relationship between thickness and t e m p e r a t u r e coefficient of resistance. The t e m p e r a t u r e coefficient of thick films can be related to their atomic n u m b e r . The limitations of thin films as resistance t h e r m o m e t e r s in various applications have been outlined.
A Semi-Conducting Antimony Bolometer United Kingdom. Thin films of a semi-conducting form of a n t i m o n y p r e p a r e d b y s p u t t e r i n g from a cathode of metallic a n t i m o n y are suitable, w i t h regard to resistivity, t e m p e r a t u r e coefficient of resistance and freedom from c u r r e n t noise, for the construction of bolometers of good sensitivity and of sufficiently high resistance for m a t c h i n g into a valve amplifer. A description is given of the construction and performance of such a bolometer, in which the a n t i m o n y film is deposited on a thin plastic pellicle. (Author)
An Improved Helium Liquefier and Cryostat United Kingdom. The rate of production of liquid helium by small scale liquefier-cryostat combinations of the D a u n t and Mendelssohn design has hitherto been limited to 4-5 cm3/min, and the m a x i m u m v o l u m e produced has been 250 cm. 3 W i t h such e q u i p m e n t the evaporation loss is low and a m o u n t s to 1-2 cm.a/h. The s y s t e m s are free from c o n t a m i n a t i o n and, therefore, the design is very convenient for investigations of the b e h a v i o u r of helium II. The a p p a r a t u s here described retains the a d v a n t a g e s of the old design b u t gives a higher o u t p u t rate and a total volume of 750 cm. 3 of liquid helium. The Joule T h o m s o n m e t h o d of cooling is used as before b u t the heat interchangers have been redesigned and a metal reservoir has been incorporated inside the evacuated casing to hold liquid h y d r o g e n boiling u n d e r reduced v a p o u r pressure. H y d r o g e n c o n s u m p t i o n is t h e r e b y decreased and the reservoir can be replenished in less t h a n one m i n u t e as against 5-10 m i n u t e s w i t h the old-type liquifier. By omitting the cooling well at the top of the old-type liquefier, liquid oxygen c o n s u m p t i o n is reduced a n d the control k n o b of the expansion valve never becomes frozen. Precooling of compressed helium to liquid oxygen t e m p e r a t u r e now takes place outside the main a p p a r a t u s . Details of the construction and a time table of the liquefaction process are given.
Multiple Target Nuclear Magnetic Resonance Cryostat United States. An a p p a r a t u s is described for controlling the t e m p e r a t u r e s to 0.1°K of several solid specimens
Ahm~t No. and References
114/II
Note by M. Varieak Rev. Sci. Instrum. ZT, Aug. 1956
655
115/II Note by O. U. Anders & W. W. Meinke Rev. Sei. Inetrum. ZT, June 1956
416-417 ll6/II
Article by T. B. Simpson & C. C. Winding A.I.Ch. E. Journal 2, March 1956 113.117 117/II Article by E. J. Gillham J. Sei. Instrum. 33~ Sept. 1956 338.341 ll8/II
Article by D. F. Brewer & D. O. Edwards J. B~. Instr~m. 33, April 1956
148-150 119/II
during nuclear magnetic resonance experiments in the range 10-400°K. The m e t h o d used is a combination of the ' t h e r m a l d a m ' and v a c u u m calorimeter. As developed, the a p p a r a t u s is used to s t u d y resonance a b s o r p t i o n
October, 1956
Vacuum Vol. V1
259
II
-
-
Vacuum
Apparatus
and Auxiliaries
--
II
Contd.
Penning Gauge as Leak Detector Yugoslavia. A modified probe gas technique for cold ionisation gauges of a n y t y p e is described which facilitates s i m u l t a n e o u s pressure m e a s u r e m e n t and leak detection b y the aid of the p o t e n t i o m e t e r method. The m e t h o d is simple, accurate and reliable over a large pressure range. The gauge used in the experiments described h a d an anode ring of m o l y b d e n u m 0.6 cm. long with internal diameter 2 cm., and t w o stainless steel cathode plates 1.5 cm. in diameter and 2.5 cm. apart. The applied anode voltage was 900 V and the magnetic field s t r e n g t h 400 G. The working range was 5 × 10 -8 to 5 × 10 -8 ram. Hg. The circuit included a galvanometer G (sensitivity 3 × 10 "g A./mm.) in series w i t h the gauge. The potential difference across G was balanced b y a cell and variable resistances. Using H , and CO 8 as probe gases, changes of pressure of ca. 10 -8 m m . H g could be detected. Use of CO, caused the discharge c u r r e n t to decrease with time, due p r o b a b l y to formation of c a r b o n a t e film on the electrodes. Using H 2, leak detection was possible over the working range of the gauge.
Beta Gauge for Localised Measurements on Thin Films United States. A device is described which allows non-destructive p o i n t - b y - p o i n t thickness m e a s u r e m e n t of films used as cyclotron targets. The film is m o u n t e d on a microscope-type moveable stage over a collimated b e t a source, a t h i n - w i n d o w Geiger t u b e being fixed above it. The source was prepared b y depositing a b o u t 5 mC of carrier-free p r o m e t h i u m chloride in a circle of a b o u t 0.05 inch diameter on a disc of 0.04 inch thick Lucite plastic. The collimator is m a d e of { inch thick Lucite with a ~ inch hole t h r o u g h it. s u r m o u n t e d b y a inch thick lead washer. The b e a m is a b o u t ~ inch in diameter and thickness variations of less t h a n 0.1 mg./sq, cm. (alumininm equivalent) can be measured for thicknesses up to a b o u t 6 mg./sq.cm. Properties of Evaporated Metal Films Related to Their Use for Surface Temperature Measurements United States. The use of e v a p o r a t e d metal films as resistance t h e r m o m e t e r s for surface t e m p e r a t u r e measurem e n t s is described. The properties of thin films of the m o s t chemically inert and refractory, metals h a v e been studied so t h a t stable resistance t h e r m o m e t e r s can be obtained. W i t h films 300-3,000 A thick, accuracies of 0.01°C have been obtained for useful periods of time. The a d v a n t a g e s of thin films in this application a r e : - (i) L o w t h e r m a l capacity of the element. (if) Simple resistance m e a s u r e m e n t (iii) Surface t o p o g r a p h y is unchanged. The useful t e m p e r a t u r e range is from r o o m t e m p e r a t u r e up to a b o u t 300°C for Co, Cr, Ni and P t films. The m e t h o d s of p r e p a r a t i o n include the use of resistance heated v a p o u r sources and also sources heated b y electron b o m b a r d m e n t a t 4 kV and "up to 0.5A. A large n u m b e r of trial r u n s were carried out to establish a s t a n d a r d technique of m a n u f a c t u r e and use of the films. The mechanical and chemical resistance were c o m p a r e d for different metals b y m e a n s of abrasion t e s t s and etching tests. I n general, the thin films were found to have a greater chemical resistance t h a n the bulk metals. The films were aged artificially b y heating at least to the t e m p e r a t u r e of operation, and this is discussed fully in relation to the m e t h o d of film preparation. G r a p h s h a v e been plotted which s h o w the relationship between the resistivity of film and of bulk metal, and the relationship between thickness and t e m p e r a t u r e coefficient of resistance. The t e m p e r a t u r e coefficient of thick films can be related to their atomic n u m b e r . The limitations of thin films as resistance t h e r m o m e t e r s in various applications have been outlined.
A Semi-Conducting Antimony Bolometer United Kingdom. Thin films of a semi-conducting form of a n t i m o n y p r e p a r e d b y s p u t t e r i n g from a cathode of metallic a n t i m o n y are suitable, w i t h regard to resistivity, t e m p e r a t u r e coefficient of resistance and freedom from c u r r e n t noise, for the construction of bolometers of good sensitivity and of sufficiently high resistance for m a t c h i n g into a valve amplifer. A description is given of the construction and performance of such a bolometer, in which the a n t i m o n y film is deposited on a thin plastic pellicle. (Author)
An Improved Helium Liquefier and Cryostat United Kingdom. The rate of production of liquid helium by small scale liquefier-cryostat combinations of the D a u n t and Mendelssohn design has hitherto been limited to 4-5 cm3/min, and the m a x i m u m v o l u m e produced has been 250 cm. 3 W i t h such e q u i p m e n t the evaporation loss is low and a m o u n t s to 1-2 cm.a/h. The s y s t e m s are free from c o n t a m i n a t i o n and, therefore, the design is very convenient for investigations of the b e h a v i o u r of helium II. The a p p a r a t u s here described retains the a d v a n t a g e s of the old design b u t gives a higher o u t p u t rate and a total volume of 750 cm. 3 of liquid helium. The Joule T h o m s o n m e t h o d of cooling is used as before b u t the heat interchangers have been redesigned and a metal reservoir has been incorporated inside the evacuated casing to hold liquid h y d r o g e n boiling u n d e r reduced v a p o u r pressure. H y d r o g e n c o n s u m p t i o n is t h e r e b y decreased and the reservoir can be replenished in less t h a n one m i n u t e as against 5-10 m i n u t e s w i t h the old-type liquifier. By omitting the cooling well at the top of the old-type liquefier, liquid oxygen c o n s u m p t i o n is reduced a n d the control k n o b of the expansion valve never becomes frozen. Precooling of compressed helium to liquid oxygen t e m p e r a t u r e now takes place outside the main a p p a r a t u s . Details of the construction and a time table of the liquefaction process are given.
Multiple Target Nuclear Magnetic Resonance Cryostat United States. An a p p a r a t u s is described for controlling the t e m p e r a t u r e s to 0.1°K of several solid specimens
Ahm~t No. and References
114/II
Note by M. Varieak Rev. Sci. Instrum. ZT, Aug. 1956
655
115/II Note by O. U. Anders & W. W. Meinke Rev. Sei. Inetrum. ZT, June 1956
416-417 ll6/II
Article by T. B. Simpson & C. C. Winding A.I.Ch. E. Journal 2, March 1956 113.117 117/II Article by E. J. Gillham J. Sei. Instrum. 33~ Sept. 1956 338.341 ll8/II
Article by D. F. Brewer & D. O. Edwards J. B~. Instr~m. 33, April 1956
148-150 119/II
during nuclear magnetic resonance experiments in the range 10-400°K. The m e t h o d used is a combination of the ' t h e r m a l d a m ' and v a c u u m calorimeter. As developed, the a p p a r a t u s is used to s t u d y resonance a b s o r p t i o n
October, 1956
Vacuum Vol. V1
259