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Low-pressure diffusion of vapour from solid nitrogen
Classified abstracts 3576-3583 Ceratron is similar to that of the Bendix M306 and about an order of magnitude smaller than that of tungsten. (Japan) T Masuoka, Rev scienr Instrum, 48 (lo), 1977, 1284-1285.
33. NUCLEONICS 33 3576. Fast-neutron .sputtering of niobium. (USA) Neutron sputtering yield measurements of niobium are reported for 14.8 MeV (d, t) neutrons and for fast neutrons in the forward direction produced by 40 MeV deuteron bombardment of a thick Be target. Six irradiations were performed with 23 niobium targets with a range of 1.7 x 10” to 6.1 x lOI (r-f,I) neutrons. One irradiation was performed with five niobium targets irradiated with a range of 4.7 x lOI to 4.5 x 10” (d, Be) neutrons. Sputtering targets included single crystals and annealed and cold-worked material with various surface preparations. Target preparation overlapped or was identical, in several cases, to that used by another research group which has reported the observation of fast-neutron-induced ‘chunk’ or micrometer particle emission. Several cm2 of collector which faced Nb targets irradiated to fluences of (0.4-1.1) x 1016 (d, I) neutrons/cm* were carefully examined by scanning electron microscopy, but no evidence for neutron-produced chunk emission 20.5 pm was found. Thermal neutron activation analysis was used to determine absolute yield on most of the silicon collectors which faced the front and back surfaces of the Nb targets. These determinations indicate that the yield in atoms/neutron for a wide variety of Nb target preparations, including those which are reputed to be high-probability chunk emitters, are likely to be less than several times 10m5. The experimental procedures are presented in detail. The present results for fast-neutron sputtering yields are discussed in relation to other recent results for niobium and theoretical estimates. Limitations in our experiments and others are also discussed. The present results, as well as other recent results for niobium, indicate that neutron sputtering will not be a significant factor in the erosion of the first wall or in plasma contamination in future fusion reactors. 0 K Harling et al, J appl Phys, 48 (IO), 1977, 43 13-4327. 33 3577. Projected range calculations of radionuclide product ejection from metal surfaces by 14.8 MeV neutrons. (USA) A calculation has been made of the radionuclide product ejection from several elemental metal foils and a stainless-steel alloy foil from (n, x) reactions in a normally incident 14.8 MeV neutron flux and compared with experimental data. The recoiling heavy products from the (n, X) reactions were assumed to propagate on the average in straight lines with a definite range vs energy relationship. With this assumption, for each distance x from the surface, an angle fl,cm is found such that product nuclei at centre-of-mass angles ecm < eccm leave the material while those at angle 8”” > eccrn on the average come to rest in the material medium. Calculated sputtering rates range from slightly below to a factor of 2 above experimental values. This agreement is judged to be good considering the assumptions of the model, the assumptions used to generate the range tables, and the uncertainties in the experimentally determined sputtering rates. D L Lessor et al, J appl Phys, 48 (IO), 1977, 4337-4343. 33
An observation of optical transition radiation from 29 MeV protons crossing a vacuum-to-metal interface. (GB) Optical transition radiation is observed in the bombardment of a thin gold foil by protons of 29 MeV energy. (Canada) A Gibb et al, J Phys D: Appl Phys, 10 (IS), 1977, L203-L205. 3578.
33
Energy analysis of neutral H, D, He and Ne atoms with energies from 288 eV to 10 keV. (GB) An energy analyzer for neutral hydrogen and noble gas atoms is described. The neutral particles are ionized by electron stripping in a gas cell and the resulting ions are energy-analyzed in an electrostatic spectrometer. The instrument is absolutely calibrated with nitrogen in the gas cell. The lowest energies which can be detected are 200 eV for hydrogen, 800 eV for helium and 1 keV for neon atoms. (Germany) H Verbeek et al, J Phys E: Scienf Instrum, 10 (9), 1977, 944-949. 3579.
33
Operation of a plasma-focus device with D2 and He’. (USA) TWO plasma-focus devices at the Lawrence Livermore Laboratory, the B Division device (BDPF), with a stored energy of 73 kJ at 3580.
18 kV, and the Physics Department device (PDPF), with a stored energy of 67 kJ at 20 kV, were operated with various mixtures of D2 and He3. The purpose of the experiments was to evaluate the D-D/ D-He3 yield ratio as a diagnostic tool for determining the plasma ion temperature. Measurements were made in the high-pressure mode (total pressure of 4.0 torr for the BDPF, 7.5 torr for the PDPF), where previous measurements using carbon activation showed no significant ion acceleration to energies above the 330 keV carbon (d, n) reaction threshold. The yield from the D(d, n)He3 reaction was determined from measurements of the total neutron yield using the standard silver-activation technique. The yield from the He3(rf, p) He4 reaction was determined by measuring the reaction-product protons by copper activation. The Cu anode insert from the centre electrode was analysed for y activity following each series of shots to measure the presence of Zn 63 from the 4.21 MeV threshold CdJ(p, n)Zn6’ reaction. The thick-target yield for this reaction at the proton energy of 14.6 MeV was calculated from cross-section data, giving a value of 7.5 x 10e4 Znh3 atoms per incident proton. In operation with SO/SOatomic or molecular mixtures of D, and He3, the D-D/D-He’ yield ratio varied from a minimum of 13.6 to a maximum of 60.5. This corresponds to a plasma temperature range from 4.0 to 6.5 keV, or if a beam-target model is assumed, to a deuteron beam ranging in energy from 28 to 47 keV incident upon stationary He3 ions. Operating with fractions of He3 ranging from 0.053 to 1.0 at a total pressure of 4 torr, the D-D neutron yield showed the expected dependence on the square of the deuterium fraction (f(D)). R L Gullickson et al, J appl Phys, 48 (9), 1977, 37 18-3722. 34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND 34
Broad-frequency chopper with adjustable duty cycle. (USA) A chopping system with in si/u adjustable frequency and duty cycle has been designed and constructed for use in modulating molecular beams. Two choppers in series driven by three-phase synchronous motors are phase shifted to adjust the duty cycle. The three-phase power signal and phase lag control are synthesized with digital logic which provides for stable control of both frequency and phase lag over a broad range of frequencies (l-1000 Hz). The stability of the system is limited by the ‘hunting’ of the hysteresis motors which is less than -;t3 p’s between 100 and 1000 Hz. With the chopper blades used here the duty cycle is adjustable from O’~-SO’~. The gating function of this chopping system is displayed at 100 and 1000 Hz for duty cvcles of
34
Etfect of experiments on the density distribution in a molecular shield. (USA) A steady-state, collisionless flow analysis has been made of the density distribution within a hemisphere-disk system due to independent, uniformly distributed internal gas sources. The model may be used to estimate the density within a molecular shield, deployed from the Shuttle Orbiter, which contains internal experiments having a prescribed gas source. Contour plots of the density distribution within the system are presented for disk-to-hemisphere radius ratios of 0. I, 0.3, 0.5 and 0.7. and for disk-to-hemisphere surface emission flux density ratios of 0.01, I and 100. The hemisphere-disk system is compared to the empty hemisphere and it is found that if the disk emission flux density is the same as the hemisphere and the disk radius is not greater than one-third of the hemisphere radius, the increase in density at the centre of the hemisphere-disk system is less than 50%. J E Hueser et al, J Vat Sci Techno/, 14 (5). 1977, I1 86-l 191. 3582.
35. PROCESSING
OF MATERIALS 35
Low-pressure diffusion of vapour from solid nitrogen. (USA) A heat flow theory is presented and tested over a wide range of temperatures and pressures. D H Martin and R A Orban, J Vat Sci Technol, 14 (5), 1977, 12121213. 3583.
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33. NUCLEONICS 33 3576. Fast-neutron .sputtering of niobium. (USA) Neutron sputtering yield measurements of niobium are reported for 14.8 MeV (d, t) neutrons and for fast neutrons in the forward direction produced by 40 MeV deuteron bombardment of a thick Be target. Six irradiations were performed with 23 niobium targets with a range of 1.7 x 10” to 6.1 x lOI (r-f,I) neutrons. One irradiation was performed with five niobium targets irradiated with a range of 4.7 x lOI to 4.5 x 10” (d, Be) neutrons. Sputtering targets included single crystals and annealed and cold-worked material with various surface preparations. Target preparation overlapped or was identical, in several cases, to that used by another research group which has reported the observation of fast-neutron-induced ‘chunk’ or micrometer particle emission. Several cm2 of collector which faced Nb targets irradiated to fluences of (0.4-1.1) x 1016 (d, I) neutrons/cm* were carefully examined by scanning electron microscopy, but no evidence for neutron-produced chunk emission 20.5 pm was found. Thermal neutron activation analysis was used to determine absolute yield on most of the silicon collectors which faced the front and back surfaces of the Nb targets. These determinations indicate that the yield in atoms/neutron for a wide variety of Nb target preparations, including those which are reputed to be high-probability chunk emitters, are likely to be less than several times 10m5. The experimental procedures are presented in detail. The present results for fast-neutron sputtering yields are discussed in relation to other recent results for niobium and theoretical estimates. Limitations in our experiments and others are also discussed. The present results, as well as other recent results for niobium, indicate that neutron sputtering will not be a significant factor in the erosion of the first wall or in plasma contamination in future fusion reactors. 0 K Harling et al, J appl Phys, 48 (IO), 1977, 43 13-4327. 33 3577. Projected range calculations of radionuclide product ejection from metal surfaces by 14.8 MeV neutrons. (USA) A calculation has been made of the radionuclide product ejection from several elemental metal foils and a stainless-steel alloy foil from (n, x) reactions in a normally incident 14.8 MeV neutron flux and compared with experimental data. The recoiling heavy products from the (n, X) reactions were assumed to propagate on the average in straight lines with a definite range vs energy relationship. With this assumption, for each distance x from the surface, an angle fl,cm is found such that product nuclei at centre-of-mass angles ecm < eccm leave the material while those at angle 8”” > eccrn on the average come to rest in the material medium. Calculated sputtering rates range from slightly below to a factor of 2 above experimental values. This agreement is judged to be good considering the assumptions of the model, the assumptions used to generate the range tables, and the uncertainties in the experimentally determined sputtering rates. D L Lessor et al, J appl Phys, 48 (IO), 1977, 4337-4343. 33
An observation of optical transition radiation from 29 MeV protons crossing a vacuum-to-metal interface. (GB) Optical transition radiation is observed in the bombardment of a thin gold foil by protons of 29 MeV energy. (Canada) A Gibb et al, J Phys D: Appl Phys, 10 (IS), 1977, L203-L205. 3578.
33
Energy analysis of neutral H, D, He and Ne atoms with energies from 288 eV to 10 keV. (GB) An energy analyzer for neutral hydrogen and noble gas atoms is described. The neutral particles are ionized by electron stripping in a gas cell and the resulting ions are energy-analyzed in an electrostatic spectrometer. The instrument is absolutely calibrated with nitrogen in the gas cell. The lowest energies which can be detected are 200 eV for hydrogen, 800 eV for helium and 1 keV for neon atoms. (Germany) H Verbeek et al, J Phys E: Scienf Instrum, 10 (9), 1977, 944-949. 3579.
33
Operation of a plasma-focus device with D2 and He’. (USA) TWO plasma-focus devices at the Lawrence Livermore Laboratory, the B Division device (BDPF), with a stored energy of 73 kJ at 3580.
18 kV, and the Physics Department device (PDPF), with a stored energy of 67 kJ at 20 kV, were operated with various mixtures of D2 and He3. The purpose of the experiments was to evaluate the D-D/ D-He3 yield ratio as a diagnostic tool for determining the plasma ion temperature. Measurements were made in the high-pressure mode (total pressure of 4.0 torr for the BDPF, 7.5 torr for the PDPF), where previous measurements using carbon activation showed no significant ion acceleration to energies above the 330 keV carbon (d, n) reaction threshold. The yield from the D(d, n)He3 reaction was determined from measurements of the total neutron yield using the standard silver-activation technique. The yield from the He3(rf, p) He4 reaction was determined by measuring the reaction-product protons by copper activation. The Cu anode insert from the centre electrode was analysed for y activity following each series of shots to measure the presence of Zn 63 from the 4.21 MeV threshold CdJ(p, n)Zn6’ reaction. The thick-target yield for this reaction at the proton energy of 14.6 MeV was calculated from cross-section data, giving a value of 7.5 x 10e4 Znh3 atoms per incident proton. In operation with SO/SOatomic or molecular mixtures of D, and He3, the D-D/D-He’ yield ratio varied from a minimum of 13.6 to a maximum of 60.5. This corresponds to a plasma temperature range from 4.0 to 6.5 keV, or if a beam-target model is assumed, to a deuteron beam ranging in energy from 28 to 47 keV incident upon stationary He3 ions. Operating with fractions of He3 ranging from 0.053 to 1.0 at a total pressure of 4 torr, the D-D neutron yield showed the expected dependence on the square of the deuterium fraction (f(D)). R L Gullickson et al, J appl Phys, 48 (9), 1977, 37 18-3722. 34. ELECTRONICS TECHNOLOGY
AND
HIGH
ALTITUDE
PHYSICS
AND 34
Broad-frequency chopper with adjustable duty cycle. (USA) A chopping system with in si/u adjustable frequency and duty cycle has been designed and constructed for use in modulating molecular beams. Two choppers in series driven by three-phase synchronous motors are phase shifted to adjust the duty cycle. The three-phase power signal and phase lag control are synthesized with digital logic which provides for stable control of both frequency and phase lag over a broad range of frequencies (l-1000 Hz). The stability of the system is limited by the ‘hunting’ of the hysteresis motors which is less than -;t3 p’s between 100 and 1000 Hz. With the chopper blades used here the duty cycle is adjustable from O’~-SO’~. The gating function of this chopping system is displayed at 100 and 1000 Hz for duty cvcles of
34
Etfect of experiments on the density distribution in a molecular shield. (USA) A steady-state, collisionless flow analysis has been made of the density distribution within a hemisphere-disk system due to independent, uniformly distributed internal gas sources. The model may be used to estimate the density within a molecular shield, deployed from the Shuttle Orbiter, which contains internal experiments having a prescribed gas source. Contour plots of the density distribution within the system are presented for disk-to-hemisphere radius ratios of 0. I, 0.3, 0.5 and 0.7. and for disk-to-hemisphere surface emission flux density ratios of 0.01, I and 100. The hemisphere-disk system is compared to the empty hemisphere and it is found that if the disk emission flux density is the same as the hemisphere and the disk radius is not greater than one-third of the hemisphere radius, the increase in density at the centre of the hemisphere-disk system is less than 50%. J E Hueser et al, J Vat Sci Techno/, 14 (5). 1977, I1 86-l 191. 3582.
35. PROCESSING
OF MATERIALS 35
Low-pressure diffusion of vapour from solid nitrogen. (USA) A heat flow theory is presented and tested over a wide range of temperatures and pressures. D H Martin and R A Orban, J Vat Sci Technol, 14 (5), 1977, 12121213. 3583.
201