On (n, γ) recoil energy spectra, primary retention, and appearance energy of hot atom

The report proposes a compact BASIC program on a personal computer for the calculation of recoil energy spectra using the Monte Carlo simulation method, presents calculated recoil energy spectra for some nuclides, and discusses appearance energies obtained from the spectra in relation to observed primary retention in some compounds. Recoil energy spectra are calculated for 51Cr, 55Cr and 103Ru from recent cascade γ-ray data. Integral spectra deduced from the calculations can serve to estimate the appearance energies (threshold energies), below which recoil atoms escape from their original sites. Good agreement is seen between the appearance energy determined here and a generally assumed threshold energy. This demonstrates that kinetic excitation plays major roles in 51Cr and 103Ru recoil processes while the contribution of other excitation mechanisms such as electronic excitation following internal conversion of a low energy γ-ray is negligible. Even if some important part of cascade information is not available, it is possible in some cases to envisage a rough profile of a recoil energy spectrum. (N.K.)