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° 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.
A single crystal neutron spectrometer has been constructed which shows improvement in resolution and intensity over previously described instruments. This has been made possible by the high flux available from the Chalk River heavy water reactor. The instrument can be operated automatically.
Mechanical design, crystals, resolution and the contamination of the spectrum by higher orders are discussed.
The angular variation of the scattering of neutrons of 0.0724 ev. energy by deuterium gas has been measured. Comparison with theoretical calculations of this variation gives a ratio of scattering lengths:[Formula: see text]In combination with the known total scattering cross section of the free deuteron of 3.44 ± 0.06 barns this gives for the scattering lengths the two sets of values:[Formula: see text]
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