597. Monochromator for the extreme ultraviolet.

Classified abstracts 593-605 and positive potentials caused by positive ions formed by electron impact in the gun have been observed. The life of those local modifications of potential are highly pressure dependent. Y Petit-Clere and J D Carette, Vacuum, 18 (1), Jan 1968, 7-16 (in French and English). 33 : 20 593. Measurement of the optical properties or alloys in ultrahigh vacuum. (Great Britain) An apparatus is described in which the optical constants of bulk alloys may be measured in ultrahigh vacuum, by using polarimetric methods over a spectral range or 0.2 to 2.7 microns and temperatures in the range 77-950°K. The vacuum system uses two VacIon pumps which are separated by a bakeable valve. With the first ion pump working, the specimen chamber, the second pump and the open valve were baked. After the baking cycle was finished the valve was closed, the baked pump took over and the first was disconnected. This left the vacuum system free to move for optical alignment. G P Palls, J Sci Instrum, 44 (12), 1967, 997-1000. 33 594. Preparation of contamination-free tungsten specimens for the field-ion microscope. (Great Britain) In a search for a suitable electrolyte for preparation of tungsten specimens it was found that backpolishing in an aqueous solution of 20 per cent potassium sulphite with an addition of 0.5 per cent hydroquinone produces a clean surface, using ac of at least 10 V, and a second electrode of gold. (Sweden). J E Fasth et al, J Sci lnstrum, 44 (12), 1967, 1044-1045. 33 595. An interferometric study of a high-intensity, hollow-cathode source. (USA) A high-intensity hollow-cathode source is described. The tube comprises a hollow copper cathode and nickel anode, the supports of which are sealed into a standard glass press. The Pyrex envelope also contains two side arms opposite each other. A thoria-coated tungsten auxiliary electrode is supported inside each side arm. The source is connected to an ultrahigh vacuum and gas-handling system and after the entire system is baked at 350°C for 20 hrs the residual pressure in the system decreases to 5 × 10-1° torr with a rate of rise of pressure in the isolated system of 10-1° torr/min, under conditions of no pumping by the ionization gauge. The source is filled with either neon or argon to a pressure of a few torr. It was found that the enhanced intensity from this source, compared with that from a conventional hollow-cathode source, is accompanied by a considerable decrease in the self-absorption of the resonance line within the source. D K Davies, J Appl Phys, 38 (12), 1967, 4713-4720. 33 596. Dielectric and optical properties of crystalline argon. (USA) Crystalline argon was grown in tubes with both rectangular and circular cross section. Pure argon was used in the system and the growing tube chamber was pumped down to 10-4 torr before the argon was admitted. The solid was deposited from the vapour near the triple point temperature. I Lefkowitz et al, J Appl Phys, 38 (12), 1967, 4867-4873. 33 597. Monochromator for the extreme ultraviolet. (USA) A monochromator designed for the investigation of clean solid surfaces is described. Differential pumping in three stages allows operation without windows with the systems still attaining pressures in the 10-9 torr range in the measuring chamber. Vacuum chambers and the vacuum system are described in detail and the operation of the system is discussed. R C Jaklevic and I J Leblanc, Rev Sci lnstrum, 38 (11), 1967, 15971601. 33 598. High intensity nozzle beam source for use in molecular total cross section measurements. (USA) A nozzle source which produces beams of neutral molecules, a factor of 10= to 103 more intense than that from effusive sources, is described. Differential pumping is used, the skimmer-collimator section having an oil diffusion pump and the collimator-detection chamber an Orbitron pump. Typical pressures during operation are 200 torr in the nozzle, 5 × 10-s torr in the nozzle-skimmer chamber and 10-9 torr in the other regions. J G Skofronick, Rev Sci Instrum, 38 (11), 1967, 1628-1631.

248

33 599. Vacuum microbalance for 77.3°K operation. (USA) A quartz oscillator vacuum microbalance that can be operated a t low temperatures is described. It has been operated at 77.3°K in the 10 10 torr range. R J Whitefield and J J Brady, Rev Sci Instrum, 38 (i 1), 1967, 16701671. 33 600. Large-energy, large-angle electron-impact spectra: helium, nitrogen, ethylene, and benzene. (USA) Electron-impact spectra taken at a fixed scattering angle of 90 ° and a variety of energies frorA 10 to 40 eV are reported for helium, nitrogen, ethylene, and benzene. The types of transitions observed (forbidden singlet-triplet and triplet) are discussed. The basic instrument used in the studies has been described in another publication (J Chem Phys, 45, 1065, 1966). Modifications to this basic instrument are discussed. The instrument was housed in an ultrahigh vacuum system which could be baked to 400°C. J P Doering and A J Williams, J Chem Phys, 47 (10), 15th Nov 1967, 4180~185. 33 601. Rate of attachment of gaseous electrons to nitrogen dioxide.

(USA) The rates of attachment of gaseous thermal electrons (300°K) to NO,~ in the presence of several inert gases have been measured. In the pressure range from 3 to 70 ram, the rate of attachment is independent of the pressure, but dependene on the nature of the inert gas. Details of the apparatus are given. A bakeable system was used in which pressures down to 10 7 torr could be obtained using an oil diffusion pump. A mechanism is proposed that accounts for the observations. B H Mahan and C Walker. J Chem Phys, 47 (I0), 15th Nov 1967, 3780-3782. 33 602. Scattering of thermal energy gas beams by metallic surfaces. (USA) Scattering of molecular gases from platinum and tantalum was studied using an ultrahigh vacuum molecular beam apparatus. Beams of the rare gases, nitrogen, oxygen, methane, and water vapour were used. The angle of maximum intensity of the scattered gas beams had a dependence on experimental variables that was in fair agreement with theory. Surface contamination and roughness affected the intensity and spatial distribution of scattered beams, but no difference between polycrystalline and single crystal metal surfaces was observed. By using phase-sensitive detection techniques, the velocity of scattered molecules was found to vary with angular position about the surface. Energy and momentum coefficients were evaluated from the experimental data. The experimental results were used in analysis of free molecular and slip flows. J J Hinchern et al, Rep F910439-7; AD-653720, June 1967, 99 pages (Sci Tech Aerospace Reps, 5 (20), 3691, N67-34246). 33 603. Optical properties of refractive electron systems. (USSR) Optical properties of electron systems consisting of two-dimensional electric and magnetic fields are analyzed. The given equations are discussed from the point of view of mass and beta spectrometers design. V M Kel'man and E M Yakushev, Zh Tekh Fiz, 37 (12). Dec 1967, 2121-2136 (in Russian). 33 604. Dynamics of particle motion in a single electrode resonant electron discharge taking into account the space charge. (USSR) The electron motion is theoretically analyzed for the unstable regime when dc and hf fields in a gap are such that an electron leaving the anode falls back to the anode with a delay equal to the hf field period and when the anode secondary emission coefficient is higher than 1 so that the instability has an avalanche character. V I Petranin, Zh Tekh Fiz, 37 (12), Dec 1967, 2239-2243 (in Russian). 33 605. Disc beam in an deetrostatie field. (USSR) Equations are derived for the thin disc electron beam in a transaxiallysymmetric electrostatic field and solved for the radial motion of the