Fundamentals of a modified model of the distribution of neutron-resonance widths and results of its application in the m
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CLEI Theory
Fundamentals of a Modified Model of the Distribution of Neutron-Resonance Widths and Results of Its Application in the Mass-Number Range of 35 ≤ A ≤ 249 A. M. Sukhovoj* and V. A. Khitrov** Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received May 31, 2012
Abstract—A modified model is developed for describing the distribution of random resonance width for any nuclei. The model assumes the coexistence in a nucleus of one or several partial radiative and neutron amplitudes for respective resonance widths, these amplitudes differing in their parameters. Also, it is assumed that amplitude can be described by a Gaussian curve characterized by a nonzero mean value and a variance not equal to unity and that their most probable values can be obtained with the highest reliability from approximations of cumulative sums of respective widths. An analysis of data for 157 sets of neutron widths for 0 ≤ l ≤ 3 and for 56 sets of total radiative widths has been performed to date. The basic result of this analysis is the following: both for neutron and for total radiative widths, the experimental set of resonance width can be represented with a rather high probability in the form of a superposition of k ≤ 4 types differing in mean amplitude parameters. DOI: 10.1134/S1063778813010146
1. INTRODUCTION
model approximation of the level density is likely to decrease with respect to 2Δ0 at each step n of the aforementioned change. Within the model concepts used in [3, 4], this change is due to the appearance of two additional independent quasiparticles as soon as the next threshold excitation energy of the nucleus being considered is reached. But according to the theoretical analysis performed by Malov and Soloviev in [6], the degree of fragmentation of any nuclear state belonging to the n quasiparticles ⊗m phonons type in the region around Bn cannot be identical because of their different positions on the energy scale of the nucleus being considered. On the basis of developments of the quasiparticle–phonon model of the nucleus and on the basis of data from experiments [3, 4] of the type implemented for the first type, it would be natural to expect that, at different excitation energies of the nucleus, changes in the probabilities for various decay processes may manifest themselves in neutronresonance wave functions. In order to test these possibilities, it is mandatory to meet the following two conditions: (i) The first is that of employing, in an analysis of experimental data, an algorithm featuring the least possible number of model concepts. (ii) The second is that of performing a quantitative comparison of two or several versions of the approximation of experimental distributions of resonance widths on the basis of different models.
In 1936, N. Bohr put forth the hypothesis [1] that the structure of high-lying levels of a compound nucleus is extremely complicated. Since that time, the properties of neutron resonances have been described within a statistical approach. However, experience gained in scie
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