The neutron resonances of selenium have been studied by a wide variety of methods over the energy range from a few electron volts to several keV. The measured values of the total cross section are presented for the range from 100 eV to about 5 keV. Information from transmission measurements on enriched samples and from capture gamma-ray spectra are used to make isotopic assignments of resonances. The capture gamma-ray data are also used for spin assignments. Complete sets of parameters are determined for most of the many resonances below 2 keV assigned to ${\mathrm{Se}}^{77}$ and for the resonances below 5.5 keV assigned to the even-even targets. Average values of spacings and strength functions are deduced. The strength functions for ${\mathrm{Se}}^{76}$ and ${\mathrm{Se}}^{77}$ are (${1.6}_{-0.7\mathrm{}}^{+3.2\mathrm{}}$)×${10}^{-4\mathrm{}}$ and (${1.7}_{-0.4\mathrm{}}^{+1.8\mathrm{}}$)×${10}^{-4\mathrm{}}$, respectively. These relatively large values reinforce the previously reported observation of an intermediate structure in the dependence of strength function on nuclear size, an effect that has been interpreted as evidence for the influence of two-particle one-hole states. The question of a possible spin dependence of the strength function is discussed.

• Received 26 June 1964

DOI:https://doi.org/10.1103/PhysRev.136.B703