摘要:

R-matrix analyses of neutron-induced reactions for many of the lightest p-shell nuclei are difficult due to a lack of distinct resonance structure in the reaction cross sections. Initial values for the required R-matrix parameters, Eλand γλcfor states in the compound system, can be obtained from shell model calculations. In the present work, the results of recent shell model calculations for the lithium isotopes have been used in R-matrix analyses of6Li+n and7Li+n reactions for En8 MeV. Consequences of the shell model redictions for the level structure of7Li and8Li on the6Li+n and7Li+n reaction mechanisms and cross sections are discussed.

ISSN:0033-7579    

DOI:10.1080/00337578608208665

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

High resolution proton resonance measurements provide a new test of the nuclear statistical model. For a sequence of levels with the same spin and parity the width correlation ρW and the amplitude correlation ρa are determined separately for the inelastic decay channels. The observed correlations average about 0.5 and are ascribed to direct reactions between the inelastic channels. For a multivariate Gaussian distribution ρ2A/ρW= 1. The present data provide the first opportunity to test this prediction directly.

ISSN:0033-7579    

DOI:10.1080/00337578608208666

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The semi-classical and quantum-mechanical theories of pre-equilibrium processes in nuclear reactions are reviewed, with special attention to the exciton, hybrid and unified models, and the Feshbach-Kerman-Koonin quantum mechanical theory. The results of the 'International Nuclear Model and Code Comparison on Pre-Equilibrium Effects' carried out under the auspices of the NEA Data Bank are presented. The quantum-mechanical theory is described and selected data for pre-equilibrium processes in93Nband59Coare analysed using both the semi-classical models and the quantum mechanical theory. The future development of analyses of pre-equilibrium processes is discussed with particular reference to the scopes of the various models and their optimum areas of applicability.

ISSN:0033-7579    

DOI:10.1080/00337578608208667

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This paper briefs the non-statistical processes in neutron radiative capture reactions such as potential-valence captures, direct-semidirect captures, and captures in the compound elastic and inelastic channels, their physical significances and calculational expressions. Then a code GRS to calculate gamma-ray production data resulting from neutron induced reactions as well as relevant cross sections is described. In addition to multistep Hauser-Feshbach model, special attention has been paid to the calculation of higher energy gamma-rays, mainly produced by the non-statistical processes.

ISSN:0033-7579    

DOI:10.1080/00337578608208668

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The statistical exciton model following the master-equation approach has been improved and extended for application as an evaluation tool of double-differential reaction cross sections at incident nucleon energies of 5 to 50 MeV. For this purpose the code system GRAPE, centered around the exciton-model code GRYPHON has been developed, which combines a number of interesting features such as: unified treatment of pre-equilibrium and equilibrium processes, renormalized exciton state-densities summing up to the back-shifted Fermi gas formula, a new model for the internal transition rates based upon the nucleon mean free path in nuclear matter, angle-energy distributions based on intra-nuclear scattering in nuclear matter, account of discrete-level excitations, a new model for γ-ray competition, inclusion of multi-particle emission, and various sorting options with code output in the new ENDF-VI format. A major characteristic of the proposed model is that consistency with equilibrium models has been imposed upon the summed exciton-state densities as well as upon the particle and γ-ray emission cross sections.

ISSN:0033-7579    

DOI:10.1080/00337578608208669

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A non-relativistic spherical optical model for neutron scattering has been parametrized for A>53 and 10 < E < 80 MeV. The model is based on σ() and Ay() data for neutrons and protons, and on total and reaction cross sections for neutrons. Qualitatively good fits to the large body of neutron data were achieved using customary Woods-Saxon form factors and reasonable well depths and geometry parameters.

ISSN:0033-7579    

DOI:10.1080/00337578608208670

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Complete lack of experimental data on (n, xn)-reaction for Pu isotopes has stimulated the development of theoretical models for evaluation of nuclear data. The models employed include the coupled-channel method, multistep statistical model, precompound emission model, superfluid nuclear level density model involving collective effects. As an example, the neutron cross sections of238-244Pu are analysed. The fission cross section data as well as the data on σnxn, σnnand neutron spectra can be correlated fairly well if collective, shell and deformation effects in neutron and fission channels are taken into account.

ISSN:0033-7579    

DOI:10.1080/00337578608208671

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The parameters of an R-matrix analysis that includes data for all reactions open in the7Li system at Ex≤ 10 MeV suggest that deuteron exchange contributes to the low-energy6Li(n, t) reaction. A method for including this mechanism directly in the theory is discussed and preliminary results are given.

ISSN:0033-7579    

DOI:10.1080/00337578608208672

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We develop a new perspective upon the differences between the hybrid and exciton models for precompound decay. Their difference in status regarding the type of cross-section being calculated, is demonstrated. Here, the treatment of multiple emission plays an important role. Statistical a priori hypotheses and possible future development of the considered models are discussed.

ISSN:0033-7579    

DOI:10.1080/00337578608208673

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Pairing corrections in particle-hole (exciton) state-density formulas used in precompound nuclear reaction theories are, strictly speaking, dependent on the nuclear excitation energyUand the exciton numbern. A general formula for (U, n)-dependent pairing corrections has been derived in an earlier paper for exciton state-density formulas for one kind of Fermion. In the present paper, a similar derivation is made for two kinds of Fermions. It is shown that the constant-pairing-energy correction used in standard level-density formulas, such asUoin Gilbert and Cameron, is a limiting case of the present general (U, n)-dependent results.

ISSN:0033-7579    

DOI:10.1080/00337578608208674

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor