On the Inelastic Scattering of Fast Neutrons

The available data on the inelastic scattering of fast neutrons are interpreted in terms of: (1) a detailed theory, developed in this paper, for the excitation of individual levels of the target nucleus, applicable when only a few levels of the target nucleus are involved (i.e., incident neutron energy only a few times the low lying level spacing of the target nucleus); or (2) the statistical theory of Weisskopf, applicable when the incident neutron energy is very much greater than the level spacing of the target nucleus (very many levels involved). The data of the Los Alamos group on the scattering of 1.5- and 3-Mev neutrons by Fe, W, and Pb indicate that Fe requires the first type of interpretation, W the second; Pb seems to be more similar to Fe than to W. The level system proposed by Elliott and Deutsch on the basis of $\beta$-decay measurements is sufficient to explain the Fe data. The average spacing of the lowest W levels is derived to be approximately 80 kev. The large apparent level spacing of Pb is consistent with the stability of nuclei containing the "magic number" of 82 protons or 126 neutrons.