Classified Abstracts 91-99 25

so that ionization of the helium is only produced at metallic atoms projecting at the surface of the wire and the resultant image gives a picture of the actual atomic structure existing at the point. The apparatus required is simple and relatively cheap. It gives moreover information not readily obtainable with the much more elaborate and expensive standard electron microscope. Magnification of the order of IO8 is obtainable and the field ion microscope is proving a useful tool in the examination of grain boundary defects and the study of the structure of solid solutions. w. I. s.

Anon., New Scientist, 16 (311), 1 Nov. 1962, 263.

33 91. World’s biggest radio valve. Great Britain. A travelling wave tube is described in which the vacuum portion consists of a stainless steel tube 10 ft long and 4 ft in diameter. The tube is exhausted by a standard system of backing and diffusion pumps and the vacuum subsequently maintained by a 400 I./set vacion pump. The tube will emit microwaves in pulses lasting Spsec and reaching 100 MW peak power. It was designed by the Services Electronics Research Laboratory and will be operated by Marconi for research into the upper atmosphere. w. 1. s.

Anon., New Scientist, 16 (312), 8 Nov. 1962, 321.

33 92. Electronic valve generating light waves. United States. A novel vacuum device known as the Varotron is described. It generates a thin beam of electrons which are passed over the surface of an insulated metallic diffraction grating engraved with 45,000 lines to the inch. Under these conditions, oscillating positive charges are induced in the grating. These charges with their associated electrons act as oscillating dipoles, i.e. electromagnetic radiators. The wavelength depends on the velocity of the electron relative to the grating as well as on the spacing of the lines in the letter. The device is tunable over the frequency range 300 to 600 x 10le c/set and the radiations thus extend well into the optical range. w. J. s.

Anon., New Scientist, 16 (314), 22 Nov. 1962, 442.

33 93. Design and construction of a glass envelope closely coaxial to a high-power electron beam. United States. A close-wound helix of 0.010 in. dia. tungsten wire has been successfully bonded into the bore of a 24-in. long, 0.625 in. dia. glass tube by shrinking the glass over the mandrel- supported helix. The additional problem of furnishing a non- magnetic glass-to-metal seal on one end of the glass cylinder has been answered by adapting a new seal combination of molyb- denum and alumino-silicate glass in cylindrical form.

(Authors)

J. A. Snyder and E. C. Steed, Rev. Sci. Instrum., 33 (9), Sept. 1962, 943-945.

33 : 14 Theory and application of molecular beam techniques for the design of collision-free sampling systems. See Abstr. No. 4.

33 : 18 : 32 Viscosity coefficient of a plasma in a magnetic field. See Abstr. No. 10.

33 : 18 : 32 Microwave generation of the second harmonic in a plasma. See Abstr. No. 11.

33 : 18 : 31 Breakdown condition in an azimuthal discharge. See Abstr. No. 12.

33 : 18 : 32 On the stability of a magnetically compressed plasma surface. See Abstr. No. 13.

33 : 18 : 32 Theory of the magnetic shock tube with varying driving magnetic field. See Abstr. No. 15.

33 : 18 High efficiency low-pressure ion source. See Abstr. No. 14.

33 : 30 : 56 Stress and magnetic anistropy in thin permalloy films. See Abstr. No. 61.

34. High Altitude and Space Technology

34 94. Test chamber reaches the stars. Anon., Iran Age, 190 (lo), 6 Sept. 1962, 77.

34 95. Canned space for earth use (3000 ft3 at 4 - 10-O torr). Anon., J. Instrum. Sot. Amer., 9 (8), Aug. 1962, 18.

96. How materials behave in space. 34

L. D. Jaffe and J. B. Rittenhouse, Mater. Design Engng, 56 (3), Sept. 1962, 97-104.

34 : 54 97. Effect of ultra-high vacuum on viability of micro-organisms. United States. Three species of resistant micro-organisms were exposed for 5 days to ultra-high vacuum approaching that of interplanetary space in order to assay the effect of this environ- ment on their viability. In addition a lower vacuum (4 x

10-e mmHg), N, + CaSO,, Na alone, air + CaSO,, and air only, were used to compare the impact of these environments. Vacuums of lo-lo mmHg as well as storage in a nitrogen atmo- sphere were shown to be the environments most conductive to preservation of the microbial organism. In fact, under the two vacuum conditions, bacillus subtilis showed better preservation than the control. L. E. P.

D. M. Portner, D. R. Spiner, R. K. Hoffman and C. R. Phillips, Science, 134 (3495), 22 Dec. 1961, 2047.

36. Drying, Degassing and Concentration

36 98. Degassing nickel. Great Britain. The average amount of gas evolved from different samples of commercially “ pure ” nickel wire was 5 ml/g at a pressure of 1 torr and a temperature of 900°C. It comes off mainly as carbon monoxide and emanates originally from the oxides of magnesium, silicon and carbon that lie near the surface of the wire. The rate of evolution besides depending on temperature and total amount of gas present is also affected by the rate of diffusion of carbon in the nickel. These results form the first step towards specifying optimum production conditions for the degassification of nickel valve components.

W. J. S.

Anon., New Scientist, 14 (282), 12 April 1962, 33.

36 : 16 99. Degassing and permeation of gases in tube materials. Great Britain. The permeation of gases through tube materials is expressed in 1~ of gas passing through 1 cm* of material, 1 mm thick, per hour, one side being at atmospheric pressure and the other at lo-’ torr. This coefficient will obviously increase with temperature of the gas. In the case of hydrogen, permeation through Monel, stainless steel 304, Kovar, nickel and 52 alloy was rapid, the coefficient increasing from 1O-5 lp/hr/cma/mm at room temperature to approximately unity