I N a paper with the above title, Smith 1 has calculated the interchange of energy between a beam of electrons and a microwave field inside a resonator. An experiment to observe the quantum nature of the energy transfer will be performed shortly in this laboratory. In order to detect this effect it is clear that the energy of the electrons must be defined with an uncertainty which is less than the quantum energy, and it is this condition that produces the experimental difficulties. By means of a time-of-flight velocity focusing tube it is hoped to produce 1000-ev electrons with a spread of 10~5 v.The approximation made in Smith's treatment is essentially to treat the electron as classical and the field as quantized. It would seem, however, more appropriate to the experimental conditions to treat the electron as quantized and the field as classical. Under these conditions the phase integral approximation should give an accurate prediction of the probabilities of energy transfer. Assuming an electric field En sincot across the resonator gap of width a, it is found that the probability of an electron gaining or losing r quanta in passing through the field is 7r 2 (s), where J r {z) is the Bessel function of rih. order, and z=(eaEo/hoj)(sm^0/^0). 0 is the transit angle defined by 0 = au/v, with v the electron velocity.This result may be understood from the fact that the Broglie waves of the electron are phase-modulated as they pass though the gap. In the limit of large numbers of quanta transferred, this distribution tends to the classical distribution. R ADIOACTIVE Co 60 , obtained from the AEC 1 was used as a tracer element in the study of self-diffusion in cobalt. This isotope has two gamma-ray spectra of energies 1.30 and 1.16 Mev, and a beta-ray spectrum of energy 0.31 Mev, necessitating a careful determination of the absorption coefficient which is essential in the method used for calculating the self-diffusion coefficient. In the present work this quantity was determined directly, in such a way as to approximate as nearly as possible the conditions present in the diffusion samples.Samples of pure cobalt were coated with radioactive Co 60 and placed in pairs, with active faces together, into a furnace which was evacuated to a pressure of less than 10~5 mm of Hg. Diffusion runs were made at temperatures of 1050°C, 1150°C, and 1250°C for 18 hours.The mathematical analysis given by Steigman, Shockley, and Nix 2 relating the fraction of counts remaining after diffusion to the diffusion coefficient, D, was used to determine D. A plot of \nD versus 1/T gave the activation constant, A, and the activation energy, Q, where D=Ae-Q> RT .The data indicate that the self-diffusion coefficient for cobalt is given approximately by D=0.367e-67000^7 ' cm 2 sec.-1 .Good agreement was found between the value of Q obtained from the plot of \nD versus 1/T and the value obtained from the Langmuir-Dushman equation
D=(Qd?/Nh)e~V RT ,where N is 6.06 X10 23 mole -1 , h is Planck's constant, and d is the lattice constant. S UBSTANTIAL inc...
