Classified Abstracts strutted in which specimens can be tilted through f25” about mutually perpendicular axes in the focal plane of the Siemens electron microscope. This has been achieved kinematically in the very limited space available without introducing any (Authors) undue friction, shake or lost motion. D. C. Barnes and E. Warner, 1962, 264-265.
Brit. J. Appl. Phys., 13 (6), June 33
314. Characteristics of a point cathode triode electron gun. Great Britain. An investigation has been carried out into the behaviour of the system obtained when a small pointed cathode is applied in a triode electron gun. The dependence of the gun current, brightness, source position and other important properties upon the geometrical and electrical parameters of the gun is reported, and some conclusions are drawn about the mechanism In particular it is shown that no appreciable of beam formation. field-enhancement of the emission occurs in this type of gun. (Authors) D. W. Swift and W. C. Nixon, Brit. J. Appl. Phys., 13 (6), June 1962, 288-293. 33 315. Method of preparing Si and Ge specimens for examination by transmission electron microscopy. Great Britain. A jet chemical polishing method suitable for preparing Si and Gk specimens for examination by transmission For Si a HNO,/HF solution electron microsconv is described. is used, while forAGe either a HNO,/HF or a Na’CIO solution Electron micrographs is used. The method is simple and rapid. (Authors) illustrating the method are given. G. R. Booker and R. Stickler, Brit. J. Appl. Phys., 13 (8), Aug. 1962, 446-448. 33 316. On the backscattering of electrons from solids. Z. T. Body, Brit. J. Appl. Phys., 13 (8), Aug. 1962, 483-485. 33 317. The kinetics and efficiency of cathodoluminescence. Great Britain. The various stages in excitation of luminescence by cathode rays are examined with the object of assessing the possible efficiency of energy conversion. It is shown that reflection of primary electrons constitutes a major loss of energy. The elastic scattering process responsible is dependent on coulomb interaction between the electrons and the atoms of the solid. Energy losses inside the phosphor due to ionization At follow a fairly simple relation to residual electron energy. all but low electron energies the relation yields a modified Thomson-Whiddington range energy law. After cascade production of secondary electrons a relatively uniform volume of excitation results, bounded in most cases by the phosphor surface where loss of electrons occurs as secondary emission. Secondary electrons incapable of further ionization will undergo phonon interaction with further energy loss to the luminescence process. At thermal velocities they will be available for radiative recombination. Approximate theoretical conversion efficiencies should be in the region of 25 per cent. An experimental estimate for ZnS-Ag phosphors gives 23 per cent which is in close agreement. The relations, found experimentally for microcrystalline phosphor layers, between luminescence, primary electron energy and beam current density can ‘only be qualitatively related to the detailed process of excitation. However, more accurate interpretations are possible for data obtained by use of single crystals. (Author) G. F. J. Garlick, Brit. J. Appl. Phys., 13 (1 l), Nov. 1962, 541-547. 33 : 58 318. Use of a three-circle goniometer for diffraction measurements. Great Britain. The principles governing the use of a three-circle
314-323
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goniometer for diffraction measurements are discussed. The vertical circle of the goniometer can be set at any arbitrary angle to the incident beam and this angle determines both the number of accessible hkl reflections and the azimuth of the hkl plane in (Author) the reflecting position. B. T. M. Willis, Brit. J. Appl. Phys., 13 (ll), Nov. 1962, 548-550. 33 319. Commemoration of the Fiftieth Anniversary of the Discovery of X-ray Diffraction and of Crvstal Structure Analysis. _ _ Munich. July 1962. Conference Report, Bri?. J. Appl. Phys., 13 (12), Dec. 1962, 577. 33 : 37 320. Electron diffraction for the magnetic analysis of an antiferromagnetic substance. Japan. It is demonstrated that the process of electron diffraction is of use for the determination of the antiferromagnetic structure of nickel oxide (NiO). Magnetized nickel oxide powder in which a small amount of ferromagnetic nickel (about 5 per cent by weight) is evenly dispersed serves as the specimen for the diffraction experiment. The (111) diffraction corresponding to the antiferromagnetic spin planes in NiO appears anomalously strong. The present process is quite similar to that using (Author) neutron diffraction. S. Yamaguchi,
Brit. J. Appl. Phys., 13 (12), Dec. 1962, 587-588.
33 321. Some effects of electric fields on the cathodoluminescence of zinc sulphide single crystals. D. W. Satchell, Brit. J. Appl. Phys., 13 (12), Dec. 1962, 589-595.
36.
Drying, Degassing and Concentration
36 322. Advances in milk processing methods-special report. U.S.A. The article includes brief references to the vacuumfoam method of drying whole milk and to developments in freeze-drying. The whole milk is concentrated, homogenized and chilled, then foamed by dispersing nitrogen into it. The foam is fed through nozzles on to a belt driver under 16 mm vacuum. The shelf-life of the product is short. Much effort is now being devoted to larger freeze-drying plant with shorter cycles and automatic loading. It has been shown that higher initial temperatures in the process make it possible to shorten D. A. P. the cycle and reduce cost. Anon., Food Engng, 34 (2), Feb. 1962, 37-52. 36 323. A short guide to freeze-drying. Great Britain. After a brief introduction, the author outlines a classification of foodstuffs according to their freeze-drying properties. The factors governing the method of cooling are then discussed and it is stressed that the optimum procedure for each type of food varies to avoid damage to the food cell structure. The main types of freeze-drying equipment are briefly described and control instrumentation is mentioned. The vapour and air extraction systems are of five types : these are : (a) steam-operated vacuum augmentors, (b) scraper icecondensers ; (c) liquid absorption systems ; (d) batch-loaded systems. Types ice-condensers ; and (e) granular absorption (a), (b) and (c) dispose of extracted moisture continuously ; the other systems store or dispose of it intermittently. Only (a) and (d) are yet of any commercial significance. This review article is concluded by some remarks on packaging, storage and D. A. P. reconstitution of the product. J. M. Dalgleish, Food Manufacture, 37 (4), April 1962, 148-156. The accelerated freeze-drying Abstr. No. 361.
method of food preservation.
36 See