Exciton model formulations for angular distributions and data comparison at medium energies

Abstract

Dedicated to Professor Theo Mayer-Kuckuk on the occasion of his 60th birthday The generalized exciton model for preequilibrium reactions is reviewed and reformulated to allow the study of different model assumptions. New models emerge from this task. All models are tested against data. Some of them are able to reproduce data up to some hundreds of MeV bombarding energies.

Particle-hole state densities with linear momentum and angular distributions in preequilibrium reactions

“…[1]. The numerical difficulties inherent in Madler and Reif's state density calculations lead to Machner devoting only two sentences to this procedure in his review "Exciton Model Formulations for Angular Distributions and Data Comparison at Medium Energies" [12]. Since we have presented new techniques for determining state densities with linear momentum which are free from computational difficulties, we believe that this procedure for calculating angular distributions should be reconsidered.…”

“…In our model, though, the equiprobability assumption leads to difFerent angular distributions for particle emission from later preequilibrium states, as compared to a folding of KK kernels [22]. It avoids the ambiguity of how such a folding of KK kernels should be applied, as is evident from the many possibilities described in Machner's review [12]. (8) We have performed a number of calculations, for a range of preequilibrium states, to compare how angleintegrated emission rates based on state densities with linear momentum compare with the "conventional" exciton emission rates which only use energy-dependent state densities.…”

“…[32]. The double-differential cross section for proton emission is then given by particle state density expression (12) was used to determine the energy-dependent state density, and the width of the Gaussian linear-momentum distribution was obtained with Eqs. (16) and (18).…”

“…Equation (12) allows us to write the product of E"with p" '(p, O, E") in terms of p" '(p+1, 0, E") (neglecting the small differences due to the Pauli-blocking A"h, factor), Therefore, the problem of calculating e" " reduces to that of calculating the average value of E". To do this, we note that a p-h state density may be expressed as a convolution over separate particle and hole state densities, p(p+ 1) p" '" (p+ 1 h E) This has the correct limiting solution that e"~e F when E -+ O.…”

A model for continuous particle spectra from light and heavy ion induced reactions

“…To better reproduce data especially at backward angles additional physics has been introduced thus loosing much of the simplicity of the model. Recent attempts of replacing the free nucleonnucleon scattering information by nuclear matter results approximated by a Fermi gas with and without angleenergy correlation are given in [8]. Additional attempts employ the harmonic oscillator [-9] model and refraction * Dedicated to Professor Friedel Sellschop on the occasion of his 60th birthday effects [,10, 11].…”