Studies of nuclear second moments for pre-equilibrium nuclear reaction theories ? Extension to finite-range residual interaction

Abstract

Study of the nuclear second moments, important inputs to pre-equilibrium reaction theories, is extended to residual interactions of finite range. The interactions are assumed to have general spin and isospin dependence. The second moments are found to be always positive definite for commonly used values of the interaction parameters. They seem to support the strong coupling limit of the pre-equilibrium reaction theory by Nishioka et al. [1], which would imply the modification of the phenomenological model used in analyzing experimental data. As an application of the second moments, it is also investigated how the nuclear level densities change with the parameter values of the residual interaction. The results show the important role of the residual interaction especially in the low energy region, which may greatly improve the agreement with experimental data at thermal neutron resonances.

Exciton level densities with spin and parity based on random matrix model

“…As was explained in 4.1 the strength of the residual interaction is properly reduced by factor of about 5 compared with [12][13][14]. But still the effects of residual interactions are appreciable in J~ fixed PLD, and this is expected to give better agreement with experimental data in a multistep compound reaction analysis.…”

“…fm 3 is assumed 9 This value is obtained from the energy separation between the ground 2-state and the 1.309 MeV excited 4-state of 38C1. This value is about five times as small as that used in [12][13][14] where IPM spectra are degenerate in each class (except for [14]), and the strength is chosen to simulate the realistic independent particle model spectra for m = 4 states 9 The simple interaction given by (37) seems at first to be a crude model, but the calculated jR averaged second moments agree very well with those calculated with the interaction used in shell model calculations, GGSI, GGSII, and Rosenfeld forces which were adopted in [13,14]. The averaged square of matrix elements for diagonal (V2)D and nondiagonal (U2)ND agree with GGSI and GGSII results within 20% in both cases of 4~ and 2OSpb '…”

“…The strength became about five times of that usually used in shell model calculations. In the second paper [13] the zero range residual interaction was replaced by finite range ones, and various properties had been investigated. In the last papers [14,15] realistic independent particle model (IPM) spectra were introduced.…”