Neutron Resonance Spectroscopy. III.Th232andU238

Abstract

The neutron total cross sections for ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$ have been measured from about 100 eV to 4 keV with \ensuremath{\sim}0.5 nsec/m resolution at the highest energies. The mean level spacings for these nuclei have been observed to be (17.5\ifmmode\pm\else\textpm\fi{}0.7) eV and (17.7\ifmmode\pm\else\textpm\fi{}0.7) eV. For ${\mathrm{U}}^{238}$ about 17% of the observed levels probably belong to $l=1$ and are omitted from the statistical analysis of the data. $S$-wave strength functions of (0.69\ifmmode\pm\else\textpm\fi{}0.07)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ and (0.90\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ are obtained for ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$, respectively. Detailed comparisons of the observed statistical aspects of the level spacings and neutron reduced width distributions have been made with the predictions of various theoretical models. The distributions of ${{\ensuremath{\Gamma}}_{n}}^{0}$ for both nuclei seem to be consistent with a single-channel Porter-Thomas distribution. The observed distributions of nearest- and next-nearest-neighbor level spacings agree quite well with the expected distributions for real symmetric Hamiltonian matrices with randomly distributed matrix elements. The correlation coefficients for ${\mathrm{Th}}^{232}$ and ${\mathrm{U}}^{238}$ are, respectively: (a) (-0.21\ifmmode\pm\else\textpm\fi{}0.07) and (-0.26\ifmmode\pm\else\textpm\fi{}0.08) for adjacent level spacings, (b) (-0.03\ifmmode\pm\else\textpm\fi{}0.07) and (-0.17\ifmmode\pm\else\textpm\fi{}0.07) for adjacent reduced neutron widths, and (c) (0.12\ifmmode\pm\else\textpm\fi{}0.07) and (0.15\ifmmode\pm\else\textpm\fi{}0.07) for the neutron reduced width of a level and the average of its spacing from adjacent levels.

Neutron Resonance Spectroscopy. III.Th232andU238

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