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A source of power pulses of soft bremsstrahlung
Classified abstracts 3430-3442 33. NUCLEONICS
34
33 3430. Coherent radiation of a modulated rectilinear relativistic electron beam. (USSR) Coherent electromagnetic radiation of a modulated relativistic electron beam in air at pressures ranging from 10T2 to 760 torr is investigated experimentally. The modulation frequency was 3000 MHz, the electron energy 5 MeV A V Abramov et al, Zh Te/ch Fiz, 45 (l), 1975,185-187 (in Russian).
3437. Surface-plasma source of negative ions. (USSR) A power pulse source of negative ions with planotron geometry of discharge chamber is described. A H- beam with a density up to 3.7 A/cm’ in the emission slit has been obtained due to intensive emission of negative ions from cathode surface under its bombardment with fast particles from the discharge in hydrogen and caesium vapours. The total current of negative hydrogen ions is up to 0.88 A. Yu 1 Belchenko et al, Zh Tekh Fiz, 45 (l), 1975, 68-73 (in Russian).
33 3431. Lass in beams of hydrogen negative ions at acceleration in linear accelerators up to energy of hundreds MeV. (USSR) It is shown that the loss in negative hydrogen ion beam in linear accelerators by electron detachment is caused mainly by residual gas in the beam canal. The residual gas pressure should be less than 5 X lo-’ to 1 X lo-’ torr in a linear accelerator for an energy of 100 to 1000 MeV. The usual composition of residual gas is considered. E K Gefand et al, Z/I Tekh Fiz, 45 (1). 1975, 74-78 (in Russian).
3438.
34
A source of power pulses of soft bremsstrahlung. (USSR) A source of power pulses of bremsstrahlung is described, which is based on an electron gun with plasma cathode and anode. The source generates stable pulses of X-rays with an effective energy of 15 to 20 keV and exposure dose of 80 at a 5 cm distance from the target centre. The source is placed in a steel vessel evacuated to 10m6 tot-r. D V Iremashvili and T .A Osepashvili, Prib Tekh Eksper, No 1, 1975, 213-214 (in Russian).
35. PROCESSING
OF MATERIALS 35
34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND
34 3432. Channel plate multiplier as an emissive mode detector in the SEM. (USA) A channel plate multiplier was placed between the specimen and scintillator to increase the number of secondary electrons in the emissive mode of operation of the SEM. A comparison between this system and the conventional scintillator detector shows that the presence of the plate improves the signal-to-noise ratio. (GB) M S Hill and A Gopinath, Rev Sci Instrum, 48 (7), 1977, 806-808.
3439. An upper bound to the outgassing rate of metal surfaces. (USA) An upper bound to the outgassing rate of low-surfacearea metal surfaces after an atmospheric exposure is deduced from a recently derived model. The result is Q,,,., = 1.72 x 10-s/t (torr l)/(s cm’) where t is in seconds. Comparisons of outgassing data with this estimate are made for (1) various low-surface-area materials, (2) a given surface at elevated temperatures and (3) a variation in the real pumping speed for a particular surface. Q,.. has been found to be an upper bound to the outgassing data under a variation of the above parameters provided that the material is operated at ~100°C for times between 15 min and 7 days. D Edwards, J Vat Sci Technol, 14 (4), 1977,1030-1032.
34
Focusing properties of an anode-controlled telefocus keV electron gua. (USA) A new design of a triode telefocus keV electron gun is presented, of which the focal distance can be varied during operation of the gun by axially adjusting the anode. The dependence of the maximum beam current density on geometrical and electrical quantities has been investigated in the neighbourhood of the beam crossover, yielding the basic data for optimizing the gun performance under given experimental boundary conditions. At a crossover distance of 0.27 m a beam width (FWHM) of 65 tirn corresoondina to a current density of 3.1 x lo4 Am-’ w& attained at an a&elerat& voltage of 17.5 kV. (Germany) B Schiewe et al, Rev Sci Instrum, 48 (7), 1977,893-896. 3433.
34
3434. High-temperature atomic beam source. (USA) A novel atomic beam source which employs radiant heating is described. It is capable of stable continuous operation for many hundreds of hours at temperatures up to 3000 K. Rapid recharging of source materials and temperature recycling may be carried out. J A Stockdale et al, Rev Sci Znstrum, 48 (7), 1977,938-939. 34
3435. Sensors for investigation of heat transfer in gases in external fields. (USSR) Construction of a heat sensor with gold film evaporated on mica substrate for measurement of small changes in heat flow in rarefied gases in external fields is described. At a nitrogen pressureof 5 x 10e2 torr, the time constant is 5 s and the threshold sensitivity for change in heat flow is 10e5. V D Barman et al, Prib Tekh Eksper, No 2,1975,232-233 (in Russian). 34
The intbrence of inclination of field boundaries of an electrostatic energy analyser on its ion-optical characteristics. (USSR) The influence of inclination of field boundaries of an 85.5” spherical sector electrostatic energy analyser on its focal length, dispersion and inclination of the focusing curve is studied both theoretically and experimentally. The experimental results show that refraction of ion trajectories on field boundaries has to be accounted at calculation of characteristics of electrostatic energy analysers. GA Samsonov et al, Prib Tekh Eksper, No 2,1975,46-47 (in Russian). 3436.
36. VACUUM STUDIES
INSTRUMENTATION
FOR
SURFACE 36
3440. Surface structures of compound semiconductors. (USA) A survey is given of surface-structure determinations for the low index faces of compound semiconductors via analyses of elastic low-energy electron diffraction intensities. The (100) face of (cubicNaCl structure) MgO is thought to exhibit a surface structure that differs little from that of a truncated bulk crystal. Small deviations from the truncated bulk geometry have been reported for the layered transition-metal dichalcogenides MO& and NbSe,. The cleavage faces of tetrahedrally coordinated compound semiconductors (i.e. zincblende (110). wurtzite (1O’fO) and wurtzite (1120)) exhibit the same space-group symmetryas the bulk crystal. The positions of the species in the uppermost atomic layer may be altered substantially from their bulk values, however, with the anion shifted outward, the cation inward, and the whole layer relaxed toward the bulk crystal. For the materials examined to- date (i.e. GaAs(llO), ZnSe (llO), ZnO(lOi0) and ZnO(ll?!O)) the shifts in atomic oosition vary in magnitude but can exert profound effects on the el&tronic structure and chemical behaviour of the associated surfaces. C B Duke, J Vat Sci Technol, 14 (4), 1977,870-877. 36
3441. Si (111) 7 x 7 surface structure. (USA) A comparison between a kinematic analysis of the fractional-order LEED-pattern symmetries of the Si (111) 7 x 7 structure and experimental data is presented. The surface model comprises a rippling of the first two double layers so as to produce interference in the coherent scattering from this distortion. The ripple deformation is small. It is treated as a perturbation in the analysis. Thus, the surface is nearly ideally terminated; there are no vacancies or adatoms in the model. Triagonal symmetry reversals are observed in the LEED patterns at about 20 V intervals and are also computed theoretically. J D Levine et al, J Voc Sci Technol, 14 (4), 1977,878-882. 36
Photoemission and band-structure studies of the GaAs (110) surface. (USA) We have studied the electronic and geometrical structure of the cleaved GaAs (110) surface, using experimental ultraviolet photoemission spectroscopy (UPS) of both tilled and empty surface states 3442.
103
34
33 3430. Coherent radiation of a modulated rectilinear relativistic electron beam. (USSR) Coherent electromagnetic radiation of a modulated relativistic electron beam in air at pressures ranging from 10T2 to 760 torr is investigated experimentally. The modulation frequency was 3000 MHz, the electron energy 5 MeV A V Abramov et al, Zh Te/ch Fiz, 45 (l), 1975,185-187 (in Russian).
3437. Surface-plasma source of negative ions. (USSR) A power pulse source of negative ions with planotron geometry of discharge chamber is described. A H- beam with a density up to 3.7 A/cm’ in the emission slit has been obtained due to intensive emission of negative ions from cathode surface under its bombardment with fast particles from the discharge in hydrogen and caesium vapours. The total current of negative hydrogen ions is up to 0.88 A. Yu 1 Belchenko et al, Zh Tekh Fiz, 45 (l), 1975, 68-73 (in Russian).
33 3431. Lass in beams of hydrogen negative ions at acceleration in linear accelerators up to energy of hundreds MeV. (USSR) It is shown that the loss in negative hydrogen ion beam in linear accelerators by electron detachment is caused mainly by residual gas in the beam canal. The residual gas pressure should be less than 5 X lo-’ to 1 X lo-’ torr in a linear accelerator for an energy of 100 to 1000 MeV. The usual composition of residual gas is considered. E K Gefand et al, Z/I Tekh Fiz, 45 (1). 1975, 74-78 (in Russian).
3438.
34
A source of power pulses of soft bremsstrahlung. (USSR) A source of power pulses of bremsstrahlung is described, which is based on an electron gun with plasma cathode and anode. The source generates stable pulses of X-rays with an effective energy of 15 to 20 keV and exposure dose of 80 at a 5 cm distance from the target centre. The source is placed in a steel vessel evacuated to 10m6 tot-r. D V Iremashvili and T .A Osepashvili, Prib Tekh Eksper, No 1, 1975, 213-214 (in Russian).
35. PROCESSING
OF MATERIALS 35
34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND
34 3432. Channel plate multiplier as an emissive mode detector in the SEM. (USA) A channel plate multiplier was placed between the specimen and scintillator to increase the number of secondary electrons in the emissive mode of operation of the SEM. A comparison between this system and the conventional scintillator detector shows that the presence of the plate improves the signal-to-noise ratio. (GB) M S Hill and A Gopinath, Rev Sci Instrum, 48 (7), 1977, 806-808.
3439. An upper bound to the outgassing rate of metal surfaces. (USA) An upper bound to the outgassing rate of low-surfacearea metal surfaces after an atmospheric exposure is deduced from a recently derived model. The result is Q,,,., = 1.72 x 10-s/t (torr l)/(s cm’) where t is in seconds. Comparisons of outgassing data with this estimate are made for (1) various low-surface-area materials, (2) a given surface at elevated temperatures and (3) a variation in the real pumping speed for a particular surface. Q,.. has been found to be an upper bound to the outgassing data under a variation of the above parameters provided that the material is operated at ~100°C for times between 15 min and 7 days. D Edwards, J Vat Sci Technol, 14 (4), 1977,1030-1032.
34
Focusing properties of an anode-controlled telefocus keV electron gua. (USA) A new design of a triode telefocus keV electron gun is presented, of which the focal distance can be varied during operation of the gun by axially adjusting the anode. The dependence of the maximum beam current density on geometrical and electrical quantities has been investigated in the neighbourhood of the beam crossover, yielding the basic data for optimizing the gun performance under given experimental boundary conditions. At a crossover distance of 0.27 m a beam width (FWHM) of 65 tirn corresoondina to a current density of 3.1 x lo4 Am-’ w& attained at an a&elerat& voltage of 17.5 kV. (Germany) B Schiewe et al, Rev Sci Instrum, 48 (7), 1977,893-896. 3433.
34
3434. High-temperature atomic beam source. (USA) A novel atomic beam source which employs radiant heating is described. It is capable of stable continuous operation for many hundreds of hours at temperatures up to 3000 K. Rapid recharging of source materials and temperature recycling may be carried out. J A Stockdale et al, Rev Sci Znstrum, 48 (7), 1977,938-939. 34
3435. Sensors for investigation of heat transfer in gases in external fields. (USSR) Construction of a heat sensor with gold film evaporated on mica substrate for measurement of small changes in heat flow in rarefied gases in external fields is described. At a nitrogen pressureof 5 x 10e2 torr, the time constant is 5 s and the threshold sensitivity for change in heat flow is 10e5. V D Barman et al, Prib Tekh Eksper, No 2,1975,232-233 (in Russian). 34
The intbrence of inclination of field boundaries of an electrostatic energy analyser on its ion-optical characteristics. (USSR) The influence of inclination of field boundaries of an 85.5” spherical sector electrostatic energy analyser on its focal length, dispersion and inclination of the focusing curve is studied both theoretically and experimentally. The experimental results show that refraction of ion trajectories on field boundaries has to be accounted at calculation of characteristics of electrostatic energy analysers. GA Samsonov et al, Prib Tekh Eksper, No 2,1975,46-47 (in Russian). 3436.
36. VACUUM STUDIES
INSTRUMENTATION
FOR
SURFACE 36
3440. Surface structures of compound semiconductors. (USA) A survey is given of surface-structure determinations for the low index faces of compound semiconductors via analyses of elastic low-energy electron diffraction intensities. The (100) face of (cubicNaCl structure) MgO is thought to exhibit a surface structure that differs little from that of a truncated bulk crystal. Small deviations from the truncated bulk geometry have been reported for the layered transition-metal dichalcogenides MO& and NbSe,. The cleavage faces of tetrahedrally coordinated compound semiconductors (i.e. zincblende (110). wurtzite (1O’fO) and wurtzite (1120)) exhibit the same space-group symmetryas the bulk crystal. The positions of the species in the uppermost atomic layer may be altered substantially from their bulk values, however, with the anion shifted outward, the cation inward, and the whole layer relaxed toward the bulk crystal. For the materials examined to- date (i.e. GaAs(llO), ZnSe (llO), ZnO(lOi0) and ZnO(ll?!O)) the shifts in atomic oosition vary in magnitude but can exert profound effects on the el&tronic structure and chemical behaviour of the associated surfaces. C B Duke, J Vat Sci Technol, 14 (4), 1977,870-877. 36
3441. Si (111) 7 x 7 surface structure. (USA) A comparison between a kinematic analysis of the fractional-order LEED-pattern symmetries of the Si (111) 7 x 7 structure and experimental data is presented. The surface model comprises a rippling of the first two double layers so as to produce interference in the coherent scattering from this distortion. The ripple deformation is small. It is treated as a perturbation in the analysis. Thus, the surface is nearly ideally terminated; there are no vacancies or adatoms in the model. Triagonal symmetry reversals are observed in the LEED patterns at about 20 V intervals and are also computed theoretically. J D Levine et al, J Voc Sci Technol, 14 (4), 1977,878-882. 36
Photoemission and band-structure studies of the GaAs (110) surface. (USA) We have studied the electronic and geometrical structure of the cleaved GaAs (110) surface, using experimental ultraviolet photoemission spectroscopy (UPS) of both tilled and empty surface states 3442.
103