The Emission and Scattering of Neutrons

Be-radon sources, which utilize as high as 1800 millicuries of radon, and probably emit about 2 to 3 million neutrons per second, were used with an ionization chamber and an amplifier system capable of detecting individual neutrons in the presence of the gamma-radiation, to investigate the emission and the properties of neutrons. The energy distribution of the neutrons emitted under the bombardment of the three groups of alpha-particles present has been studied, and the results analyzed in terms of a number of neutron groups, which are discussed in terms of transitions involving neutrons and gamma-rays, with at least one, and possibly two resonance levels. The maximum energy of the neutrons appears to be about 14.2 MEV, and indicates a neutron mass of about 1.0068. Deuterium-radon and zinc-radon have been found to give, if any, less than 1 percent of the number of neutrons emitted by Be-radon. The interaction of high energy neutrons with matter seems to be largely one of approximately elastic collisions with atomic nuclei, resulting in scattering of the neutrons. The scattering of neutrons has been studied using interposed cylindrical specimens to scatter neutrons away from the ionization chamber, and using toroidal specimens to scatter neutrons into the ionization chamber. The collision areas computed from the scattering measurements increase with atomic weight in a manner that indicates that the effective volume of the nucleus is proportional to its atomic weight, but the classical elastic sphere collision theory is inadequate, and a wave theory of scattering must be used to obtain consistent quantitative results. The neutron "radius" indicated is of the order of 1.2×${10}^{-13\mathrm{}}$ cm, and the nuclear radii appear to vary about as ${\left(\mathrm{atomic}\mathrm{weight}\right)}^{\frac{1}{3}}$, ranging from 2.5×${10}^{-13\mathrm{}}$ cm for lithium to 7.8×${10}^{-13\mathrm{}}$ cm for lead.