Cadmium Filters Research Articles

Measurements of η for Pu 239 specimens containing some Pu 240, and of the effective resonance-absorption integral for Pu 240

Measurements of η have been made with the dE/E spectrum, bounded at the lower end by 0·15 eV and 0·4 eV as a result of using gadolinium and cadmium filters respectively. The various Pu 239 specimens contained 0%, 1·6%, 2·5%, 6·5%, and 16% of Pu 240. Results are also given for the effective resonance-absorption integral of Pu 240.

Measurement of the average number ?eff of neutrons emitted per single capture event for samples of Pu239 with impurities of the isotope Pu240 and the effective resonance capture integral of Pu240

In this article we present the results of measurement of νeff in Fermi spectra with lower bounds of 0.15 ev (gadolinium filter) and 0.4 ev (cadmium filter) for samples of Pu239 with various concentrations of impurities of the isotope Pu240 (0% 1.6%, 2.5%, 6.5%, 16%) and the effective resonance absorption integral of Pu240.

Energy Distribution of Slow Neutrons Scattered from Solids

The sharp dependence on energy of the cadmium cross section for neutrons of energies near 0.35 ev has been used to investigate the energy distribution of 0.35-ev neutrons scattered through 90\ifmmode^\circ\else\textdegree\fi{} by lead, aluminum, diamond, and graphite. The transmission of the scattered neutrons by cadmium filters was measured as a function of cadmium thickness and compared with cadmium transmissions calculated for an Einstein crystal model. In all cases agreement was obtained. For lead and aluminum at room temperature the simpler model of a gas of free atoms gave equally good agreement, a well-known behavior at high energies, but here applying when the temperature and neutron energy were only moderately greater than the Einstein temperature and much less than the binding energy. Theoretical formulas for the partial differential scattering cross sections for the two models are given in convenient form.

Absorption of Residual Neutrons

DR. SZILARD has observed that although cadmium has a very high absorption cross-section for slow neutrons, the residual slow neutrons not absorbed by a cadmium filter are strongly absorbed by a thin sheet of indium1. This, he points out, is in contradiction to the conclusions drawn from current theory as advanced by Fermi and others.