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Tandem cyclotron at United Institute of Nuclear Investigations
Classified
abstracts
615-627
615. Experimental investigation of anode processes with closed drift of electrons. (USSR)
32 in an accelerator
The anode region of discharge is investigated in a plasma accelerator with closed drift of electrons. The model of accelerator was examined in a vacuum chamber at a pressure of 4 x lo-“ torr. I V Melikov, Z/r T&h Fiz, 44 (l), 1974, 59-64 (in Russian). 32 616. Ion implantation: stopping and the range of ions in solids. (Czechoslovakia) A review dealing with the energy losses of ions with energy in the keV region moving in amorphous or single crystal target is given. Also computer simulation of ion implantation and the methods for measurement of implantation profiles are dealt with. J Cely, Czech JPhys, A 24 (I), 1974, 2140 (in Czech). 617. Experience
gained in the operation
of the ISR vacuum
32 system.
(USSR) A pressure of 10-r’ torr has been achieved in the proton storage rings of CERN without presence of beams. At presence of beams of 5 to 10 A currents, desorption of gas is observed from chamber walls due to bombardment with secondary ions generated by the beam in residual gas and accelerated by the beam potential. Additional pumps, high temperature degassing of the vacuum chamber, cleaning chamber walls by gas discharge in argon and using of Ti and Au coatings on chamber walls are employed to suppress the pressure increase at operation of the storage rings. E Fischer, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 101-106 (in Russian). 32 618. Ionization gauge for determination of parameters of proton beam. (USSR) An ionization gauge, based on measurement of ionization of residua1 gas by an accelerated proton beam, is used for determination of geometrical characteristics of the proton beam. Possibility of utilization of nrooer magnetic field of the accelerator in the gauge is studied. The resolution of the gauge is given by the size of me&ring tapes. E F Liuatov et al. Reo of 3rd AN-Union Conf on Accel of Charaed _ Part, Vi1 2, Nauka M&x& 1973, 148-150 (in kmian). 32 619. Features of construction of resonance system and vacuum chamber of a high-current phasotron. (USSR) The descrited synchrocyclotron uses an accelerating voltage of 50 kV,
beam current of 50 PA and repetition frequency of cycles of 600 Hz. The vacuum system of the phasotron consists of the accelerating chamber, body of frequency variators and intermediate chamber with duants. I G Vaulina et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol2, Nauka Moscow 1973, 262-265 (in Russian). 32 620. Experience gained in tbe operation of the intersecting storage ring vacuum system. (USSR) The CERN intersecting storage rings are intended for operation with 28 GeV protons at currents of 20 A. At absence of the beam, the pressure in the ring is equal to 10-i’ torr. Hydrogen with 90 to 95 % forms the main component of residual gas, traces of water vapour carbon monoxide and hydrocarbons are present. In the experiments the storage of current of 6.4 A was reached, then the current decreased and the pressure increased to 10m6 torr. The mechanism of proton current decay at low6 torr is based on the influence of negative space. charge of ionization electrons trapped by the proton beam. The residual gas spectrum at pressure increase contains 40% of hydrogen, 40% of CO and 20% of water vapour. To suppress pressure bursts, it is necessary to reduce desorption of gases from walls of the vacuum chamber, enhance pumping speed of pumps and reduce the distances between pump positions. E Fisher, Rep of 3rd Al&Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 101-106. 32 621. Vacuum systems for superconducting storage rings. (USSR) The project of colliding storage ringswith length of 2.5 km is described. The vacuum chamber, represented by a tube with a diameter of 7 cm, is thermally insulated to enable both heating and cooling down to low temperatures. To attain background residual gas concentration
of 3 x lo6 molecules/cm3 it is necessary to dislocate pumps with pumping speeds of 200 l/set ever 3 metres. J M Bittner and H J Halama, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 191-194 (in Russian). 32 622. On possibility of cryogenic pumping of proton synchrotron. (USSR) It is shown that the most efficient method is pumping by clean surfaces. In the vacuum system of a proton synchrotron with temperature of sorbing surfaces of 4.2” K, all gases, except hydrogen and helium, have equilibrium pressure less than 10-r’ torr and outgassing is determined principally by desorption of hydrogen from walls of the vacuum chamber. Heatine of the chamber for several days at 300°C reduces hydrogen outgass&g to lo- I2 torr l/cm2 sec. The equilibrium pressure depends on the density of coating of sorbing surface by molecules and at their density of lOI mol/cm* the equilibrium pressure attains 10-l’ torr. The saturation vapour pressure of hydrogen for the coating of several monolayers is 2 x 10m7 torr at 4.2” K. An analysis of operation of the system of cryogenic pumping of a synchrotron with the limiting energy of 2000 GeV and intensity of accelerated beam of lOi imp set-’ is given. V A Budkin and A A Glazkov, Rep of 3rd All-Union Conf on Acre1 of Charged Part, Vol 1, Nauka Moscow 1973, 214-216 (in Russian). 32 623. Trimuf, the meson factory in Vancouver, Canada. (USSR) The isochronous cvclotron. acceleratine H- ions to 500 MeV, is described. The pressure of 4 x lo-’ tar; in the vacuum chamter of the accelerator is generated by cryogenic pumping at 20” K. (Canada) J R Richardson, Reo of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka ii4oscow 1973,288-301. 32 624. Latest development with colliding beams in CEA. (USSR) An electron synchrotorn with limiting energy of 6 GeV is used for experiments with colliding electron and positron beams possessing energy of 2 GeV. The life time of stored beams is 1 to 2 hours at a pressure of lo-* torr in the vacuum chamber. The background pressure in the vacuum chamber is lo-” torr, the pressure in the zone of collision of beams is 10e9 torr. R Averiil et al, Proc of 3rd All-Union Conf on Acre/ of Churged Part, Vol 1, Nauka Moscow 1973, 341-348. 32 625. Experiments with a closed proton beam in ionized residual gas. (USSR) Instabilities of a closed proton beam are investigated in a ring with constant magnetic field. It is found that instabilities can develop at interaction of the proton beam with a filament of secondary electrons generated at ionization of residual gas. G I Dimov et al. Proc of 3rd All-Union Conf on Accel of Chatged Part, Vol 1, Nauka Moscaw 1973, 349-352 &Russian). 32 626. Dynamic measurements of transverse dimensions of a beam in proton synchrotron by ionization of residual gas. (USSR) An ionization profilometer has been developed for measurement of transversal dimensions of the proton beams in accelerators. The profilometer uses parallel electric and magnetic fields for extraction of electrons generated at ionization of residual gas by the accelerated proton beam. A A Kuzmin et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vo12, Nauka Moscow 1973, 144147 (in Russim). 32 627. Tandem cyclotron at United Institute of Nuclear Investigations. (USSR) A tandem
consisting of two cyclotrons and a transport system is used for acceleration of xenon ions. In the first cyclotron the 136Xe+9 ions are accelerated, and after transportation they are changed to 136Xe+30 ions and accelerated to 7 MeV/nucleon in the second cyclotron. A pressure of 2 X 10m6 torr is maintained in the first cyclotron. Losses in the transportation system are equal to 30% at residual pressure of 2 X lOm6 ton. In the second cyclotron a pressure of 5 x lo-’ torr is generated. Maximum intensity of the beam at the output of the second cyclotron is 2 x 10” particles per second. I A Shelaev et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vo12, Nauka Moscow 1973, 186-192 (in Russian). 183
Classified
abstracts
628. Reconstruction chrotron. (USSR)
628-638
of the vacuum
system
of Erevan
electron
32 syn-
The old vacuum system with metal-epoxy resin chamber sections has been replaced by high-alumina ceramical sections with constantan rings brazed with copper-silver alloy. Ceramic tubes were metallized by molybdenum-manganese mixture what serves as inner heaters. Gaskets of 2 mm diameter aluminium wire were used as mounting of the new chamber. Pumping down to 5 x 10s6 torr lasts less than 24 hours. G M Martyugov et al, Rep of 3rd All-Union Conf on Accel of Charged Part, VoZ2, Nauka Moscow 1973, 227-230 (in Russian).
33. GENERAL
PHYSICS
AND ELECTRONICS 33
629. Soft X-ray
appearance potential spectroscopy of lanthanum, gadolinium, and thorium. (USA) The electron binding energies of La (Mz-N5,4 levels), Gd (M3-N5,4
levels) and Th (OS-N1 levels) were determined by SXAPS and compared with those obtained b; ESCA and by cal&lation. The results are in reasonable agreement. The La was oxidized and the shift in the SXAPS peaks was less than 1 eV. Stellite peaks have been observed associated with the M,, M4, and N5,4 peaks of La and Gd and the O5 and O4 peaks of Th. Possible mechanisms responsible for these satellite peaks are discussed. M S Murthy and P A Redhead, J Vat Sci Technol, 11 (4), 1974, 837842. 33 530. He*
afterpulses in photomultipliers: their effect on atomic and molecular lifetime determinations. (USA) Determination of atomic and molecular lifetimes by delayed coincidence photon counting with photomultipliers two or more years old may lead to erroneous results caused by afterpulses and even direct photodecay in perfused helium. Spurious lifetimes as low as 15 nsec for the BZ&+ (0’ = 0) state of N, + and the C3 II, (u’ = 0) state of NZ have been observed. W C Paske, Rev Sci Znstrum, 45 (8), 1974, 1001-1003. 631. Electron avalanche and surface charging during pulsed high-voltage stress. (USA)
on alumina
33 insulators
This paper describes a model for insulator surface charging in highvoltage ceramic vacuum diodes. The model involves electron emission from the insulator-cathode-vacuum junction followed by electron avalanches on the insulator surface which leave the wall positively charged. Experiments were performed to measure (i) the triplejunction (cathode-vacuum-insulator interface) emission and its relation to the initiation of the avalanche, (ii) the dynamic current in the avalanche, and (iii) the saturated surface charge resulting from the avalanche. The experimental results were interpreted by computer simulation in terms of the model and were found to be in close agreement with the predictions. J P Brainard and D Jensen, J Appl Phys, 45 (8), 1974, 3260-3265. 632. Thermionic filaments. (USA)
emission
of boron-
and
lanthanum-coated
33 boron
Thermionic emission from boron filaments exposed to a lanthanum metal vapour flux was studied with a view towards development of filamentary lanthanum hexaboride (LaB6) emitters. The emission was continually monitored in both stationary and continuous coating processes.. A Richardson plot of uncoated-boron-filament emission data vields 6 = 4.38 eV and A = 22 A/cm2 OK2 for the temperature _ region 155c-1855 “K. Current densities equivalent to LaB6 emission were obtained for optimally coated filaments. Coated-filament strength data, possible reaction mechanisms, and potential process limitations are also presented. E G Wolff, J AppI Phys, 45 (9), 1974,384s3843. 33 633. The carbon-fibre field emitter. (GB)
The applications of and the problems encountered in the use of field electron emitters as cold cathode sources for electron beam devices have been reviewed. The possibility of using an etched carbon fibre as a cold electron source in such devices has been examined. A simple scanning electron microscope using a carbon184
fibre field emitter has been constructed and produced stable pictures with a resolution of approximately 0.2 pm at a system pressure of lo-’ Pa. Unlike tungsten, the fibres will emit electrons for many thousands of hours at estimated current densities of the order of lo5 A cm-2. Recently emission currents as high as 1 mA at applied voltages of approximately 3.5 kV have been obtained without any sign of breakdown after running continuously for 100 h. F S Baker et al, JPhys D: ApplPhys, 7 (15), 1974,2105-2109. 33 634. A magnetic sector atom-probe FIM. (USA) The 60” magnetic sector atom-probe field ion microscope displays a section of the momentum spectrum on a stack of microchannel plates and a proximity-focused phosphor screen. A mass resolution AM/M N l/ZOO0 is achieved, and ‘spectral lines’ made up of a few individual ions may be used for the detection and identification of products of field evaporation of metals and their compounds with adsorbate gases. The capability of the new instrument is complementary to the established ToF atom probe as it employs very low evaporation rates in slow pulse or dc field evaporation, and displays the energy distribution of field ions. As an example of the difference, a palladium-neon ion compound PdNe+ is demonstrated to be very abundant, while it is a rare species in the ToF atom probe. E W Miiller and T Sakurai, J Vat Sci Technol, 11 (5), 1974, 878-882. 33 635. Field ionizers as molecular beam detectors. (USA) The operating characteristics of field ionizing tungsten tips used as detectors of low temperature beams of 3He and 4He are presented. These include typical I-V characteristics, effective detection area, conditions for fast ionization time, and details necessary for reliable detector performance. In addition, we report that, under our operating conditions the detection efficiency was independent of the incident atom velocity. This is in contradiction to predictions from current field ionization theory. J W McWane and D E Oates, Rev Sci Znstrum, 45 (9), 1974, 11451148. 33 636. Premature field evaporation in the atom probe. (USA) The motion of ions evaporating in the subnanosecond period before a pulse has matured is invoked in the interpretation-of resolution limiting energy __ deficits in the TOF atom-probe. The second order. nonlinear differential equation of motion in the time and space dependent field is numerically solved by computer. Two shapes of the pulse front, in which the final voltage level is approached either from below or from an overshoot are considered. The latter case accounts for the actual observations by giving the proper magnitude and mass dependence of the energy deficits. S V Krishnaswamy and E W Miiller, Rev Sci Znstrum, 45 (9), 1974, 1049-1052. 33 637. Barium zirconate thermionic cathodes. (USA)
A clarification of the mechanism responsible for reported high electron emissivities of barium zirconate cathodes in the presence of electronegative gases is made. A suggestion for simplifying the preparation of such cathodes is given. C Sherman, Rev Sci Znstrum, 45 (9), 1974, 1165-l 166. 33 638. A vacuum
cell and associated optics for obtaining a singlereflection infrared spectrum using reflection-absorption spectroscopy. (USA)
A compact vacuum cell and associated optics used to obtain a singlereflection infrared spectrum of a thin film on a metal surface is described. Reflection-absorption spectroscopy, in the past, has usually involved multiple reflections. Single reflection setups offer advantages of simplicity, the ability to generate and/or clean the sample surface, and the ability to use other surface studies techniques along with ir. An optical setup is described which will allow the above three advantages to be obtained, and in addition is simple and compact. Along with the optics, a vacuum cell housing the sample is described. This cell fits conveniently with a standard infrared spectrometer and no additional modification to the spectrometer is required. H G Tompkins and D L Allata, Rev Sci Znstrum, 45 (IO), 1974, 12211223.
abstracts
615-627
615. Experimental investigation of anode processes with closed drift of electrons. (USSR)
32 in an accelerator
The anode region of discharge is investigated in a plasma accelerator with closed drift of electrons. The model of accelerator was examined in a vacuum chamber at a pressure of 4 x lo-“ torr. I V Melikov, Z/r T&h Fiz, 44 (l), 1974, 59-64 (in Russian). 32 616. Ion implantation: stopping and the range of ions in solids. (Czechoslovakia) A review dealing with the energy losses of ions with energy in the keV region moving in amorphous or single crystal target is given. Also computer simulation of ion implantation and the methods for measurement of implantation profiles are dealt with. J Cely, Czech JPhys, A 24 (I), 1974, 2140 (in Czech). 617. Experience
gained in the operation
of the ISR vacuum
32 system.
(USSR) A pressure of 10-r’ torr has been achieved in the proton storage rings of CERN without presence of beams. At presence of beams of 5 to 10 A currents, desorption of gas is observed from chamber walls due to bombardment with secondary ions generated by the beam in residual gas and accelerated by the beam potential. Additional pumps, high temperature degassing of the vacuum chamber, cleaning chamber walls by gas discharge in argon and using of Ti and Au coatings on chamber walls are employed to suppress the pressure increase at operation of the storage rings. E Fischer, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 101-106 (in Russian). 32 618. Ionization gauge for determination of parameters of proton beam. (USSR) An ionization gauge, based on measurement of ionization of residua1 gas by an accelerated proton beam, is used for determination of geometrical characteristics of the proton beam. Possibility of utilization of nrooer magnetic field of the accelerator in the gauge is studied. The resolution of the gauge is given by the size of me&ring tapes. E F Liuatov et al. Reo of 3rd AN-Union Conf on Accel of Charaed _ Part, Vi1 2, Nauka M&x& 1973, 148-150 (in kmian). 32 619. Features of construction of resonance system and vacuum chamber of a high-current phasotron. (USSR) The descrited synchrocyclotron uses an accelerating voltage of 50 kV,
beam current of 50 PA and repetition frequency of cycles of 600 Hz. The vacuum system of the phasotron consists of the accelerating chamber, body of frequency variators and intermediate chamber with duants. I G Vaulina et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol2, Nauka Moscow 1973, 262-265 (in Russian). 32 620. Experience gained in tbe operation of the intersecting storage ring vacuum system. (USSR) The CERN intersecting storage rings are intended for operation with 28 GeV protons at currents of 20 A. At absence of the beam, the pressure in the ring is equal to 10-i’ torr. Hydrogen with 90 to 95 % forms the main component of residual gas, traces of water vapour carbon monoxide and hydrocarbons are present. In the experiments the storage of current of 6.4 A was reached, then the current decreased and the pressure increased to 10m6 torr. The mechanism of proton current decay at low6 torr is based on the influence of negative space. charge of ionization electrons trapped by the proton beam. The residual gas spectrum at pressure increase contains 40% of hydrogen, 40% of CO and 20% of water vapour. To suppress pressure bursts, it is necessary to reduce desorption of gases from walls of the vacuum chamber, enhance pumping speed of pumps and reduce the distances between pump positions. E Fisher, Rep of 3rd Al&Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 101-106. 32 621. Vacuum systems for superconducting storage rings. (USSR) The project of colliding storage ringswith length of 2.5 km is described. The vacuum chamber, represented by a tube with a diameter of 7 cm, is thermally insulated to enable both heating and cooling down to low temperatures. To attain background residual gas concentration
of 3 x lo6 molecules/cm3 it is necessary to dislocate pumps with pumping speeds of 200 l/set ever 3 metres. J M Bittner and H J Halama, Rep of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka Moscow 1973, 191-194 (in Russian). 32 622. On possibility of cryogenic pumping of proton synchrotron. (USSR) It is shown that the most efficient method is pumping by clean surfaces. In the vacuum system of a proton synchrotron with temperature of sorbing surfaces of 4.2” K, all gases, except hydrogen and helium, have equilibrium pressure less than 10-r’ torr and outgassing is determined principally by desorption of hydrogen from walls of the vacuum chamber. Heatine of the chamber for several days at 300°C reduces hydrogen outgass&g to lo- I2 torr l/cm2 sec. The equilibrium pressure depends on the density of coating of sorbing surface by molecules and at their density of lOI mol/cm* the equilibrium pressure attains 10-l’ torr. The saturation vapour pressure of hydrogen for the coating of several monolayers is 2 x 10m7 torr at 4.2” K. An analysis of operation of the system of cryogenic pumping of a synchrotron with the limiting energy of 2000 GeV and intensity of accelerated beam of lOi imp set-’ is given. V A Budkin and A A Glazkov, Rep of 3rd All-Union Conf on Acre1 of Charged Part, Vol 1, Nauka Moscow 1973, 214-216 (in Russian). 32 623. Trimuf, the meson factory in Vancouver, Canada. (USSR) The isochronous cvclotron. acceleratine H- ions to 500 MeV, is described. The pressure of 4 x lo-’ tar; in the vacuum chamter of the accelerator is generated by cryogenic pumping at 20” K. (Canada) J R Richardson, Reo of 3rd All-Union Conf on Accel of Charged Part, Vol 1, Nauka ii4oscow 1973,288-301. 32 624. Latest development with colliding beams in CEA. (USSR) An electron synchrotorn with limiting energy of 6 GeV is used for experiments with colliding electron and positron beams possessing energy of 2 GeV. The life time of stored beams is 1 to 2 hours at a pressure of lo-* torr in the vacuum chamber. The background pressure in the vacuum chamber is lo-” torr, the pressure in the zone of collision of beams is 10e9 torr. R Averiil et al, Proc of 3rd All-Union Conf on Acre/ of Churged Part, Vol 1, Nauka Moscow 1973, 341-348. 32 625. Experiments with a closed proton beam in ionized residual gas. (USSR) Instabilities of a closed proton beam are investigated in a ring with constant magnetic field. It is found that instabilities can develop at interaction of the proton beam with a filament of secondary electrons generated at ionization of residual gas. G I Dimov et al. Proc of 3rd All-Union Conf on Accel of Chatged Part, Vol 1, Nauka Moscaw 1973, 349-352 &Russian). 32 626. Dynamic measurements of transverse dimensions of a beam in proton synchrotron by ionization of residual gas. (USSR) An ionization profilometer has been developed for measurement of transversal dimensions of the proton beams in accelerators. The profilometer uses parallel electric and magnetic fields for extraction of electrons generated at ionization of residual gas by the accelerated proton beam. A A Kuzmin et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vo12, Nauka Moscow 1973, 144147 (in Russim). 32 627. Tandem cyclotron at United Institute of Nuclear Investigations. (USSR) A tandem
consisting of two cyclotrons and a transport system is used for acceleration of xenon ions. In the first cyclotron the 136Xe+9 ions are accelerated, and after transportation they are changed to 136Xe+30 ions and accelerated to 7 MeV/nucleon in the second cyclotron. A pressure of 2 X 10m6 torr is maintained in the first cyclotron. Losses in the transportation system are equal to 30% at residual pressure of 2 X lOm6 ton. In the second cyclotron a pressure of 5 x lo-’ torr is generated. Maximum intensity of the beam at the output of the second cyclotron is 2 x 10” particles per second. I A Shelaev et al, Rep of 3rd All-Union Conf on Accel of Charged Part, Vo12, Nauka Moscow 1973, 186-192 (in Russian). 183
Classified
abstracts
628. Reconstruction chrotron. (USSR)
628-638
of the vacuum
system
of Erevan
electron
32 syn-
The old vacuum system with metal-epoxy resin chamber sections has been replaced by high-alumina ceramical sections with constantan rings brazed with copper-silver alloy. Ceramic tubes were metallized by molybdenum-manganese mixture what serves as inner heaters. Gaskets of 2 mm diameter aluminium wire were used as mounting of the new chamber. Pumping down to 5 x 10s6 torr lasts less than 24 hours. G M Martyugov et al, Rep of 3rd All-Union Conf on Accel of Charged Part, VoZ2, Nauka Moscow 1973, 227-230 (in Russian).
33. GENERAL
PHYSICS
AND ELECTRONICS 33
629. Soft X-ray
appearance potential spectroscopy of lanthanum, gadolinium, and thorium. (USA) The electron binding energies of La (Mz-N5,4 levels), Gd (M3-N5,4
levels) and Th (OS-N1 levels) were determined by SXAPS and compared with those obtained b; ESCA and by cal&lation. The results are in reasonable agreement. The La was oxidized and the shift in the SXAPS peaks was less than 1 eV. Stellite peaks have been observed associated with the M,, M4, and N5,4 peaks of La and Gd and the O5 and O4 peaks of Th. Possible mechanisms responsible for these satellite peaks are discussed. M S Murthy and P A Redhead, J Vat Sci Technol, 11 (4), 1974, 837842. 33 530. He*
afterpulses in photomultipliers: their effect on atomic and molecular lifetime determinations. (USA) Determination of atomic and molecular lifetimes by delayed coincidence photon counting with photomultipliers two or more years old may lead to erroneous results caused by afterpulses and even direct photodecay in perfused helium. Spurious lifetimes as low as 15 nsec for the BZ&+ (0’ = 0) state of N, + and the C3 II, (u’ = 0) state of NZ have been observed. W C Paske, Rev Sci Znstrum, 45 (8), 1974, 1001-1003. 631. Electron avalanche and surface charging during pulsed high-voltage stress. (USA)
on alumina
33 insulators
This paper describes a model for insulator surface charging in highvoltage ceramic vacuum diodes. The model involves electron emission from the insulator-cathode-vacuum junction followed by electron avalanches on the insulator surface which leave the wall positively charged. Experiments were performed to measure (i) the triplejunction (cathode-vacuum-insulator interface) emission and its relation to the initiation of the avalanche, (ii) the dynamic current in the avalanche, and (iii) the saturated surface charge resulting from the avalanche. The experimental results were interpreted by computer simulation in terms of the model and were found to be in close agreement with the predictions. J P Brainard and D Jensen, J Appl Phys, 45 (8), 1974, 3260-3265. 632. Thermionic filaments. (USA)
emission
of boron-
and
lanthanum-coated
33 boron
Thermionic emission from boron filaments exposed to a lanthanum metal vapour flux was studied with a view towards development of filamentary lanthanum hexaboride (LaB6) emitters. The emission was continually monitored in both stationary and continuous coating processes.. A Richardson plot of uncoated-boron-filament emission data vields 6 = 4.38 eV and A = 22 A/cm2 OK2 for the temperature _ region 155c-1855 “K. Current densities equivalent to LaB6 emission were obtained for optimally coated filaments. Coated-filament strength data, possible reaction mechanisms, and potential process limitations are also presented. E G Wolff, J AppI Phys, 45 (9), 1974,384s3843. 33 633. The carbon-fibre field emitter. (GB)
The applications of and the problems encountered in the use of field electron emitters as cold cathode sources for electron beam devices have been reviewed. The possibility of using an etched carbon fibre as a cold electron source in such devices has been examined. A simple scanning electron microscope using a carbon184
fibre field emitter has been constructed and produced stable pictures with a resolution of approximately 0.2 pm at a system pressure of lo-’ Pa. Unlike tungsten, the fibres will emit electrons for many thousands of hours at estimated current densities of the order of lo5 A cm-2. Recently emission currents as high as 1 mA at applied voltages of approximately 3.5 kV have been obtained without any sign of breakdown after running continuously for 100 h. F S Baker et al, JPhys D: ApplPhys, 7 (15), 1974,2105-2109. 33 634. A magnetic sector atom-probe FIM. (USA) The 60” magnetic sector atom-probe field ion microscope displays a section of the momentum spectrum on a stack of microchannel plates and a proximity-focused phosphor screen. A mass resolution AM/M N l/ZOO0 is achieved, and ‘spectral lines’ made up of a few individual ions may be used for the detection and identification of products of field evaporation of metals and their compounds with adsorbate gases. The capability of the new instrument is complementary to the established ToF atom probe as it employs very low evaporation rates in slow pulse or dc field evaporation, and displays the energy distribution of field ions. As an example of the difference, a palladium-neon ion compound PdNe+ is demonstrated to be very abundant, while it is a rare species in the ToF atom probe. E W Miiller and T Sakurai, J Vat Sci Technol, 11 (5), 1974, 878-882. 33 635. Field ionizers as molecular beam detectors. (USA) The operating characteristics of field ionizing tungsten tips used as detectors of low temperature beams of 3He and 4He are presented. These include typical I-V characteristics, effective detection area, conditions for fast ionization time, and details necessary for reliable detector performance. In addition, we report that, under our operating conditions the detection efficiency was independent of the incident atom velocity. This is in contradiction to predictions from current field ionization theory. J W McWane and D E Oates, Rev Sci Znstrum, 45 (9), 1974, 11451148. 33 636. Premature field evaporation in the atom probe. (USA) The motion of ions evaporating in the subnanosecond period before a pulse has matured is invoked in the interpretation-of resolution limiting energy __ deficits in the TOF atom-probe. The second order. nonlinear differential equation of motion in the time and space dependent field is numerically solved by computer. Two shapes of the pulse front, in which the final voltage level is approached either from below or from an overshoot are considered. The latter case accounts for the actual observations by giving the proper magnitude and mass dependence of the energy deficits. S V Krishnaswamy and E W Miiller, Rev Sci Znstrum, 45 (9), 1974, 1049-1052. 33 637. Barium zirconate thermionic cathodes. (USA)
A clarification of the mechanism responsible for reported high electron emissivities of barium zirconate cathodes in the presence of electronegative gases is made. A suggestion for simplifying the preparation of such cathodes is given. C Sherman, Rev Sci Znstrum, 45 (9), 1974, 1165-l 166. 33 638. A vacuum
cell and associated optics for obtaining a singlereflection infrared spectrum using reflection-absorption spectroscopy. (USA)
A compact vacuum cell and associated optics used to obtain a singlereflection infrared spectrum of a thin film on a metal surface is described. Reflection-absorption spectroscopy, in the past, has usually involved multiple reflections. Single reflection setups offer advantages of simplicity, the ability to generate and/or clean the sample surface, and the ability to use other surface studies techniques along with ir. An optical setup is described which will allow the above three advantages to be obtained, and in addition is simple and compact. Along with the optics, a vacuum cell housing the sample is described. This cell fits conveniently with a standard infrared spectrometer and no additional modification to the spectrometer is required. H G Tompkins and D L Allata, Rev Sci Znstrum, 45 (IO), 1974, 12211223.