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arXiv · 1804.01617

Statistical theory of deformation distributions in nuclear spectra

M. T. Mustonen·C. N. Gilbreth·Y. Alhassid·G. F. Bertsch
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Abstract

The dependence of the nuclear level density on intrinsic deformation is an important input to dynamical nuclear processes such as fission. Auxiliary-field Monte Carlo (AFMC) method is a powerful method for computing nuclear level densities. However, the statistical distribution of intrinsic shapes is not readily accessible due to the formulation of AFMC in a spherical configuration-interaction shell-model approach. Instead, theory of deformation up to now has largely relied on a mean-field approximation which breaks rotational symmetry. We show here how the distributions of the intrinsic quadrupole deformation parameters can be calculated within the AFMC method, and present results for a chain of even-mass samarium nuclei ($^{148}$Sm, $^{150}$Sm, $^{152}$Sm, $^{154}$Sm) which includes spherical, transitional, and strongly deformed isotopes. The method relies on a Landau-like expansion of the Helmholtz free energy in invariant polynomials of the quadrupole tensor. We find that an expansion to fourth order provides an excellent description of the AFMC results.

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M. T. Mustonen, C. N. Gilbreth, Y. Alhassid, G. F. Bertsch. 2018-04-04. Statistical theory of deformation distributions in nuclear spectra. https://doi.org/10.1103/physrevc.98.034317

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