Abstract
A phenomenological prediction for radiative neutron capture is presented and compared to recent compilations of Maxwellian averaged cross sections and average radiative widths. Photon strength functions and nuclear level densities near the neutron separation energy are extracted from data without the assumption of axial symmetry – at variance to common usage. A satisfactory description is reached with a small number of global parameters when theoretical predictions on triaxiality (from constrained HFB calculations with the Gogny D1S interaction) are inserted into conventional calculations of radiative neutron capture. The photon strength is parametrized using the sum of three Lorentzians (TLO) in accordance to the dipole sum rule. The positions and widths are accounted for by the droplet model with surface dissipation without locally adjusted parameters. Level densities are influenced strongly by the significant collective enhancement based on the breaking of axial symmetry. With the less stringent requirement of invariance against rotation by 180∘ a global set of parameters which allows to describe the photon strength function and the level densities in the nuclear mass range from mass number 50 < A < 250 is found.
Highlights
IntroductionA triaxial shape for heavy nuclei should provide a more general basis for the description of nuclear structure than the assumption of axial symmetry, which probably originates from atomic hyperfine structure observations [1], which are usually made on unpolarized probes and are insensitive to broken axiality
A satisfactory description is reached with a small number of global parameters when theoretical predictions on triaxiality are inserted into conventional calculations of radiative neutron capture
A triaxial shape for heavy nuclei should provide a more general basis for the description of nuclear structure than the assumption of axial symmetry, which probably originates from atomic hyperfine structure observations [1], which are usually made on unpolarized probes and are insensitive to broken axiality
Summary
A triaxial shape for heavy nuclei should provide a more general basis for the description of nuclear structure than the assumption of axial symmetry, which probably originates from atomic hyperfine structure observations [1], which are usually made on unpolarized probes and are insensitive to broken axiality. This does not exclude the possibility that certain properties as observed in certain nuclei may be reproduced well by a theoretical model based on axial or even spherical symmetry. With these quantities averaged neutron capture cross sections can be calculated and are compared with experimental Maxwellian averaged cross sections [10, 11]
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