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1247. Pressure measurements in scattering experiments
Classified abstracts 1245-1255 entails a minimum of metallic parts to minimize perturbations due to outgassing or pumping by active metal. Operation is as easy as that of the classical Bayard-Alpert gauge. It is concluded that the Groszkowski modification may lead to a new step forward in ultrahigh vacuum metrology. H Bernadet and Mile Shaw, Le Vide, 23 (134), March-April 1968, 80 86 (in French). 22 1245. New mechanical pumps without lubrication. (France) Two new series of completely dry and sealed, mechanical displacement pumps are described. These pumps were developed by the Societe de Recherches Technique et Industrielles, Boulogne, France, and will soort be available for ultrahigh vacuum operations. Both types of pump (circular and swivelling translation) are considered to have the following advantages: highly efficient gas removal; complete gas and vapour tightness (primary pump is also dry); high pressure ratio for each stage; each machine is generally two-stage 10-1/10 ~ with two pumps; and available capacity range is 10, 100, 1000, and 10,000 m3/hour. Dry pump lines are being studied for the pumping of particle accelerators. L Lemoine, Le Vide, 23 (134), March-April 1968, 87-92 (in French). 22 1246. Experiences with an absolute precision gauge calibration system. (Germany) A bakeable, three-chamber, pressure reduction system was constructed for calibrating gauges in the pressure range from 10-~ to 10-8 torr. The ionization gauges being calibrated are mounted on a 61 cm diameter, spherical chamber designed to obtain an isotropic pressure distribution under dynamic conditions. Calibrations were derived in terms of known orifice conduetances and accurate pressure determinations with a precision MeLeod gauge connected to the primary chamber. High pumping speed in the ultrahigh vacuum chamber minimized the effects of adsorption/desorption and pumping by the gauge. The use of multiple traps fully protected the system against contamination from the pumping system. B Fletcher and J F Watts, Vakuum-Technik, 17 (6), June 1968, 145-149 (in German). 22 1247. Pressure measurements in scattering experiments. (Germany) In order to avoid thermal transpiration effects, for which corrections are rather difficult to introduce, an ionization gauge of very small dimensions (0.7 cm 3 volume) and very low heat input (1 watt), was fitted to a scattering chamber. The gauge was calibrated by means of a MeLeod gauge with capillaries of 4 mm internal diameter. The accuracy of the absolute pressure measurement was within 4-1 per cent. When the temperature of the scattering chamber was lowered to that of liquid nitrogen, the sensitivity of the ionization gauge dropped by about 8 per cent. J Politick et al, Vakuum-Technik, 17 (6), June 1968, 150-152 (in
German). 22 1248. Sensitivity variations in the Bayard-Alpert ionization gauge. Part two: simulation of ion collection, for collimated beam input and chaotic gas input, using a digital computer. (Great Britain) Bayard-Alpert ionization gauges with end-caps on the grids are known to show higher sensitivity than those with open-ended grids. Since the assumption of nearly 100 per cent collection efficiency is reasonable for a closed gauge, a simulation of the open gauge has been carried out to determine whether or not this explains the effect satisfactorily. It was found that the loss of sensitivity in the absence of end-caps could only partially be explained in this way. D J Turner and C Priestland, Vacuum, 18 (6), June 1968, 319-326.
22 1249. Error due to the meniscus volume in measuring low pressures with a McLeod gauge. (Japan) Low pressure measurement by MeLeod gauge involves a relatively large error due to the meniscus volume. Using a digital computer, the accurate volumes of the mercury meniscus for capillaries were calculated from the Laplace differential equation. The results are tabulated as a function of meniscus height for radii of 0.3 to 1.0 ram. Some correction methods for pressure measurements, utilizing the table, are discussed. It has been confirmed that a formula, obtained by the spherical surface approximation, readily gives the meniscus volume, within 2 per cent error, for capillaries of 2 mm diameter or less. K Nakayama, J Vac Soc Japan, II (5), 1968, 156-164 (in Japanese).
534
22 1250. The effect of the dimensions of an omegatron on its performance. (Great Britain) The paper discusses how the dimensions of an omegatron limit its applications as a mass spectrometer and explains why most omegatrons have a comparable performance in the same magnetic field. It is concluded that it should be possible to make an omegatron which resolves, without loss of sensitivity, unit mass at the base of the resonance up to mass 100 with flux densities less than 0.5T (5 kG). B W Petley and K Morris, J Sci Instrum, Ser 2, 1 (4), 1968, 417422. 22 : 27 1251. Combined leak detector and high sensitivity vacuum gauge.
(USA) In this combined vacuum gauge (10 11 torr) and leak detector the background currents are suppressed by an appropriately disposed magnetic field. In leak detection, negative-ion-forming tracer gases such as Freon 12 can be detected at partial pressures below l0 -11 torr in the presence of common background gases at total pressures as high as 10 -4 torr. G D Perkins and C F Robinson, Rev Sci Instrum, 39 (3), 1968, 361362. 22 1252. Two modifieations of the magnetic system of a charged particle analyzer. (USSR) Double focusing magnetic spectrometers with two-sectional or in homogeneous magnetic field are theoretically discussed. Yu G Basargin, Dokl Akad Nauk SSSR, 179 (5), llth April 1968, 1074-1075 (in Russian). 22 1253. Iron-free time-of-flight mass spectrometers. (USSR) This review article deals with the theory, typical designs and applications of time-of-flight mass spectrometers. The following Soviet devices are described: MKh-5201 (range of 12 to 75 m/e, resolution 40, argon sensitivity 10-9 torr, full spectrum in 3 rain), MSKh-3A (mass range of 1 to 250, argon sensitivity 5 × 10-9 torr, resolution 20, full spectrum in 4 to 60 msec), MKh-5301 also called Khromass-1 (combined with a chromatograph, with magnetic corrections of the ion beams, range 12 to 420 m/e, resolution 100, argon sensitivity 10-9 torr, scanning frequency 10 kHz, ion flight path 50 cm) and M K h 5401 (mass range 1 to 100, resolution 16, argon sensitivity of 5 × 10-s torr, full spectrum in 16 microseconds, weight 4.3 kg). 75 references are given. V A Pavlenko et al, Zh Tekh Fiz, 38 (4), April 1968, 581-602 (in
Russian). 23. PLUMBING 23 1254. Standardization of ultrahigh vacuum flanges. (France) The work of the ISO in the standardization of vacuum flanges is briefly summarized. Seals for ultrahigh vacuum flanges are generally metallic and the methods of fabrication for gold and aluminium wire seals are presented. Based on this, a table of suggested dimensions is given for ultrahigh vacuum flanges having nominal diameters from 10 to I000. K A Ridley, Le Vide, 23 (134), March-April 1968, 75-79 (in French). 23 1255. An analysis of the vacuum sealing process between turned surfaces. (Great Britain) The technique of sealography, previously developed for homogeneously rough surfaces, is further developed to embrace vacuum seals in which the sealing surfaces have two different roughness profiles, one radial the other circumferential. Concentrically and helically machined surfaces are considered and equations expressing the characteristic curves of the sealogram are derived. The values of specific factors resulting from these equations are computed as a function of the geometric parameters of the seal. Values resulting from the sealogram are compared with the computed values. From the analytical and experimental study it is concluded that the sealing process of circumferentially machined surfaces shows various distinct stages. The first stage occurs at small tightening forces with a leak rate higher than that for homogeneously rough surfaces. At higher tightening forces a second stage is observed with a leak rate considerably lower than that for homogeneous surfaces. Under specific conditions, a third stage may exist in which the conductance is constant. For helically machined surfaces, the curve of the helical
German). 22 1248. Sensitivity variations in the Bayard-Alpert ionization gauge. Part two: simulation of ion collection, for collimated beam input and chaotic gas input, using a digital computer. (Great Britain) Bayard-Alpert ionization gauges with end-caps on the grids are known to show higher sensitivity than those with open-ended grids. Since the assumption of nearly 100 per cent collection efficiency is reasonable for a closed gauge, a simulation of the open gauge has been carried out to determine whether or not this explains the effect satisfactorily. It was found that the loss of sensitivity in the absence of end-caps could only partially be explained in this way. D J Turner and C Priestland, Vacuum, 18 (6), June 1968, 319-326.
22 1249. Error due to the meniscus volume in measuring low pressures with a McLeod gauge. (Japan) Low pressure measurement by MeLeod gauge involves a relatively large error due to the meniscus volume. Using a digital computer, the accurate volumes of the mercury meniscus for capillaries were calculated from the Laplace differential equation. The results are tabulated as a function of meniscus height for radii of 0.3 to 1.0 ram. Some correction methods for pressure measurements, utilizing the table, are discussed. It has been confirmed that a formula, obtained by the spherical surface approximation, readily gives the meniscus volume, within 2 per cent error, for capillaries of 2 mm diameter or less. K Nakayama, J Vac Soc Japan, II (5), 1968, 156-164 (in Japanese).
534
22 1250. The effect of the dimensions of an omegatron on its performance. (Great Britain) The paper discusses how the dimensions of an omegatron limit its applications as a mass spectrometer and explains why most omegatrons have a comparable performance in the same magnetic field. It is concluded that it should be possible to make an omegatron which resolves, without loss of sensitivity, unit mass at the base of the resonance up to mass 100 with flux densities less than 0.5T (5 kG). B W Petley and K Morris, J Sci Instrum, Ser 2, 1 (4), 1968, 417422. 22 : 27 1251. Combined leak detector and high sensitivity vacuum gauge.
(USA) In this combined vacuum gauge (10 11 torr) and leak detector the background currents are suppressed by an appropriately disposed magnetic field. In leak detection, negative-ion-forming tracer gases such as Freon 12 can be detected at partial pressures below l0 -11 torr in the presence of common background gases at total pressures as high as 10 -4 torr. G D Perkins and C F Robinson, Rev Sci Instrum, 39 (3), 1968, 361362. 22 1252. Two modifieations of the magnetic system of a charged particle analyzer. (USSR) Double focusing magnetic spectrometers with two-sectional or in homogeneous magnetic field are theoretically discussed. Yu G Basargin, Dokl Akad Nauk SSSR, 179 (5), llth April 1968, 1074-1075 (in Russian). 22 1253. Iron-free time-of-flight mass spectrometers. (USSR) This review article deals with the theory, typical designs and applications of time-of-flight mass spectrometers. The following Soviet devices are described: MKh-5201 (range of 12 to 75 m/e, resolution 40, argon sensitivity 10-9 torr, full spectrum in 3 rain), MSKh-3A (mass range of 1 to 250, argon sensitivity 5 × 10-9 torr, resolution 20, full spectrum in 4 to 60 msec), MKh-5301 also called Khromass-1 (combined with a chromatograph, with magnetic corrections of the ion beams, range 12 to 420 m/e, resolution 100, argon sensitivity 10-9 torr, scanning frequency 10 kHz, ion flight path 50 cm) and M K h 5401 (mass range 1 to 100, resolution 16, argon sensitivity of 5 × 10-s torr, full spectrum in 16 microseconds, weight 4.3 kg). 75 references are given. V A Pavlenko et al, Zh Tekh Fiz, 38 (4), April 1968, 581-602 (in
Russian). 23. PLUMBING 23 1254. Standardization of ultrahigh vacuum flanges. (France) The work of the ISO in the standardization of vacuum flanges is briefly summarized. Seals for ultrahigh vacuum flanges are generally metallic and the methods of fabrication for gold and aluminium wire seals are presented. Based on this, a table of suggested dimensions is given for ultrahigh vacuum flanges having nominal diameters from 10 to I000. K A Ridley, Le Vide, 23 (134), March-April 1968, 75-79 (in French). 23 1255. An analysis of the vacuum sealing process between turned surfaces. (Great Britain) The technique of sealography, previously developed for homogeneously rough surfaces, is further developed to embrace vacuum seals in which the sealing surfaces have two different roughness profiles, one radial the other circumferential. Concentrically and helically machined surfaces are considered and equations expressing the characteristic curves of the sealogram are derived. The values of specific factors resulting from these equations are computed as a function of the geometric parameters of the seal. Values resulting from the sealogram are compared with the computed values. From the analytical and experimental study it is concluded that the sealing process of circumferentially machined surfaces shows various distinct stages. The first stage occurs at small tightening forces with a leak rate higher than that for homogeneously rough surfaces. At higher tightening forces a second stage is observed with a leak rate considerably lower than that for homogeneous surfaces. Under specific conditions, a third stage may exist in which the conductance is constant. For helically machined surfaces, the curve of the helical