Effect Of High Energy Electrons Research Articles

Transmission and small-angle-scattering of 15 MeV electrons in silicon single crystals

Directional effects of high energy electrons have been studied by means of transmission experiments. Broad minima with distinct fine structure were observed in axial directions and interpreted classically as a superposition of the blocking effect and “string scattering”. In terms of wave mechanics this corresponds to the anomalous absorption effect and the excitation of Bragg resonances. The present work deals with an investigation of angular distributions of transmitted electrons. A movable detector with small aperture (≈3 × 10 −7 sr) was used for the measurements. A comparison with classical Monte Carlo calculations showed that the ring patterns in the axial case as well as the scattering distributions for random incidence cannot be described quantitatively by classical mechanics. In both cases the diffuse scattering is severely overestimated by the calculations. This discrepancy is attributed to the difference in the quantum-mechanical and classical cross sections for elastic electron scattering by screened atoms. On the other hand the “string scattering” yield corresponds roughly to the measured amplitude of excited Bragg beams; it can be shown that the quantum-mechanical cross section for correlated scattering with the atoms of a string tends to a classical limit. The experimental scattering distributions agree well with Monte Carlo calculations modified on the basis of these considerations. Temperature effects can be included by introducing Debye-Waller corrected scattering amplitudes.

LOW ENERGY ELECTRON IRRADIATION OF METHANE1,2

The composition of the condensable products of lowenergy electron irradiation of methane was examined as a function of electron energy and other conditions. Practically no variation was found in product composition over the range 700 to 1300 v. Other variables were also explored. It was also established that no significant amounts of ethylene or acetylene were produced in these experiments. A lack of significant variations in product composition with electron energy, as determined by the applied voltage, indicates that a single primary process probably is responsible for the whole spectrum of products observed. The product spectrum obtained was compared with that observed in conventional radiolysis of methane, and considerable correspondence was obtained. This suggests that the effect of high energy electrons may involve, in large part, excitation rather than ionization. (P. C.H.)