ABSTRACTS OF TECHNICAL ARTICLES 517 



Measurement of Minority Carrier Lifetime in Germanium. L. B. 

 Valdes^ LR.E,, Proc., 40, pp. 1420-1423, Nov., 1952. 



A method for measuring the lifetime of minority carriers in germanium is 

 described. Basically, it consists of liberating the carriers optically on a flat face 

 of a crystal and measuring the concentration of minority carriers as a function 

 of distance from the point of Uberation. The mathematical model is analyzed 

 and experimental results are presented here. 



Drift Velocities of Ions in Krypton and Xenon. R. N. Varney^ Phys. 

 Rev., 88, pp. 362-364, Oct. 15, 1952. (Monograph 2028). 



Drift velocities and mobihties of ions of Kr and Xe in their respective parent 

 gases have been measured over a wide range of values of E/po , the ratio of elec- 

 tric field strength to normahzed gas pressure. Two ions appear in each gas 

 identified as Kr+ and Kr2+ in Kr and Xe+ and Xe2 in Xe. The relation that drift 

 velocity varies as (E/po)^ at high E/po has been found to hold for the atomic 

 ions and has been used to determine the equivalent hard sphere cross sections 

 at high fields. The cross sections are 157 X 10"^^ cm^ for Kr and 192 X 10"^^ 

 cm^ for Xe. The Langevin theory of mobilities gives excellent agreement with 

 experimental results extrapolated to zero field strength provided that, in the 

 theory, the hard sphere cross section is taken as large for the atomic ions and 

 very small for the molecular ions. The range of the polarization forces is such as 

 to render them insignificant in atomic ion colHsons and of primary importance 

 in molecular ion colhsions. 



Junction Transistor Tetrode for High-Frequency Use. R. L. Wallace^ 

 L. G. ScHiMPFi and E. Dickten^. I.R.E., Proc, 40, pp. 1395-1400, 

 Nov., 1952. 



If a fourth electrode is added to a conventional junction transistor and biased 

 in a suitable way, the base resistance of the transistor is reduced by a very sub- 

 stantial factor. This reduction in r^, permits the transistor to be used at frequen- 

 cies ten times or more higher than would other\\'ise be possible. Tetrodes of this 

 sort have been used in sine- wave oscillators up to a frequency of 130 mc and have 

 produced substantial gain as tuned amplifiers at frequencies of 50 mc and higher. 



Nature of Solids. G. H. Wannier^. Sci. Am., 187, p. 39 Dec, 1952. 

 The theory that explains their various properties is a comparatively recent 

 development of physics. From it practical benefits already begin to flow. 



Magnetic Double Refraction at Microwave Frequencies. M. T. Weiss^ 

 and A. G. Foxi. Letter to the Editor, Phys. Rev., 88, pp. 146-147, Oct. 

 1, 1952. 



Stress Relaxation in Plastics and Insulating Materials. E. E. Wright^ 

 A.S.T.M. Bull, 184, pp. 47-49, Sept., 1952. (Monograph 2024). 



1 Bell Telephone Laboratories. 



