604 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



bonibaidinent has been determined l)y c(jllecting the internally produced car- 

 riers across a reverse-biased n-p junction. No evidence is found for trapping of 

 carriers in the barrier region. Studies of individual pulses show that the carriers 

 are s\vei)t across the barrier in a time of less than 2 X 10^ sec. The counting 

 efficiency is 100 per cent. Tlie enei'gy lost by an alpha-particle i)or internally 

 produced electron-hole pair is 3.0 ± 0.4 ev. The difference between this and the 

 energy gap is attributed to losses to the lattice b}- the internal cari'iers. It is 

 concluded that lecombination due to columnar ionization is negligible in ger- 

 maniunr. 



The n-p-n Junction as a Model for Secondary Photoconductivity. K. G. 

 McKay . Phys. Rev., 84, pp. 833-835, Nov. 15, 1951. 



A germanium n-p-n junction with the p region floating, has been suljjected 

 to alpha-particle bombardment. The transient currents resulting from indi- 

 vidual incident alphas liave been studied. This enables one to stud}' the rate 

 of deca.y of excess holes in the p-region. This decay time appears to increase 

 with applied bias, pass through a maximum, and eventuallj' approach a con- 

 stant value. The total charge flowing across the unit, as a result of the bombard- 

 ment by a single alpha-particle, maj^ become large; quantum yields of greater 

 than 60 haxe been obser\'ed. The unit possesses many of the important charac- 

 teristics of materials which exhibit "secondary photoconductivity." It is con- 

 cluded that various forms of n-p-n barriers must therefore play an important 

 role in such materials and that their understanding can he greatly facilitated 

 by studies of n-p-7i barriers in germanium. 



Frequency Detection and Speech Formants. E. Peterson . Acoustical 

 Soc. Am., JL, 23, pp. 668-674, Xov., 1951. 



This study is aimed primarily at evaluating the utility of axis-crossing de- 

 tectors in tracking speech formants. Detectors of the usual tj'pe are found sub- 

 ject to an error, fundamental in nature. To remove this source of error speech 

 is modulated up in frequency as a single sideband before limiting and detecting 

 processes are applied. Experimental results with this carrier type of detector on 

 a small number of speech samples are presented, and compared with spectro- 

 grams. Conclusions are that the average axis-crossing rates cannot be trusted 

 in general to follow specific formants, whether the speech is normal or differen- 

 tiated. But when the formants are sufficientlv localized by frequenc}' selectivity, 

 prospects of tracking the lower formants look promising. 



Transistor Circuit Design. G. Raisbeck\ Electronics, 24, pp. 128- 

 132, 134, Dec, 1951. (Monograph 1932). 



How to derive amplifier, oscillator, modulator and multi-vibrator transistor 

 circuits from known vacuum-tube circuits. Technique, known as duality, is 

 explained in detail and may be applied to any complex vacuum-tube circuit to 

 find the corresponding transistor circuit. 



Communication Theory — Exposition of Fundamentals. C. E. Shannon . 

 Pp. 44-47. General treatment of the problem of Coding. Pp. 102-104. 



1 Bell Telephone Laboratories 



