Comparison of statistical model calculations for stable isotope neutron capture

Abstract

It is a well-observed result that different nuclear input models sensitively affect Hauser-Feshbach (HF) crosssection calculations. Less well-known, however, are the effects on calculations originating from nonmodel aspects, such as experimental data truncation and transmission function energy binning, as well as code-dependent aspects, such as the definition of level-density matching energy and the inclusion of shell correction terms in the level-density parameter. To investigate these aspects, Maxwellian-averaged neutron capture cross sections (MACS) at 30 keV have been calculated using the well-established statistical Hauser-Feshbach model codes TALYS and NON-SMOKER for approximately 340 nuclei. For the same nuclei, MACS predictions have also been obtained using two new HF codes, CIGAR and SAPPHIRE. Details of these two codes, which have been developed to contain an overlapping set of identically implemented nuclear physics input models, are presented. It is generally accepted that HF calculations are valid to within a factor of 3. It was found that this factor is dependent on both model and nonmodel details, such as the coarseness of the transmission function energy binning and data truncation, as well as variances in details regarding the implementation of level-density parameter, backshift, matching energy, and giant dipole strength function parameters.

Theoretical uncertainty of(α,n)reactions relevant for the nucleosynthesis of lightr-processnuclei in neutrino-driven winds

“…Apart from this explicit level-structure dependence, whenever the excitation energies of the residue nucleus are greater than the last experimentally-known level, the sum of transmission coefficients over spins and parities must be replaced by an integral over the level density. Beard et al studied this "truncation" effect by varying the maximum number of known levels in their calculations and found that their Maxwellian-averaged neutron-capture cross sections changed by almost 20% [13].…”

“…We chose this code because it has been extensively used in many sensitivity studies involving neutron-capture reactions (e.g. [13,17]). Unlike TALYS, NON-SMOKER does not include the pre-equilibrium or direct components.…”

“…In the last years, there have been numerous studies on the role of neutron-capture rates in the nucleosynthesis of heavy elements. These studies focused on understanding the sources of uncertainty of the calculated rates [12,13], and evaluating the impact of these uncertainties in network-calculated abundances [14][15][16][17]. On the contrary, equivalent studies on charge-particle reactions are scarce [9,18,19], even though they are known to play a crucial role in the synthesis of light r-process nuclei (from Fe to Ag) through the α (or charge-particle) process (see e.g.…”

Systematic study of(α,γ)reactions for stable nickel isotopes

“…The code NON-SMOKER, used to generate the thermonuclear reaction rate library REACLIB [34] also used the CT+BSFG level density description. However it is important to stress that the implementation of the CT+BSFG model in NON-SMOKER differs from that of TALYS in a number of key respects, including the definition of the back-shift, level density and spin-cut off parameters, as well as the temperature and the CT+BSFG matching point energy [35]. When generating the BRUSLIB library [18], TALYS was operated using microscopic model 5 in the above list.…”

Estimation of M1 scissors mode strength for deformed nuclei in the medium- to heavy-mass region by statistical Hauser-Feshbach model calculations

“…RIPL-3 [6], which can be used in calculation of the statistical decay. Both the phenomenological nature of the description and the variation between models contribute to the uncertainty in the prediction of capture cross sections [7] which is further compounded by the choice of implementation in Hauser-Feshbach codes [8]. Among these models, one of the most widely used is the Generalized Lorentzian model of Kopecky et al [9].…”