Successful Prediction of Total α -Induced Reaction Cross Sections at Astrophysically Relevant Sub-Coulomb Energies Using a Novel Approach

Abstract

The prediction of stellar ðγ; αÞ reaction rates for heavy nuclei is based on the calculation of ðα; γÞ cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called p nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen α-nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary α-nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen α-nucleus potential is able to predict total α-induced reaction cross sections for a wide range of heavy target nuclei above A ≳ 150 with uncertainties below a factor of 2. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the α-nucleus potential had to be adjusted to experimental data. The new model allows us to predict the reaction rate of the astrophysically important 176 Wðα; γÞ 180 Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from A ≈ 60 up to A ≳ 200.

Low Energy measurement of the $^{96}\mathrm{Zr}(α,n)^{99}\mathrm{Mo}$ reaction cross section and its impact on weak r-process nucleosynthesis

“…The new experimental data for the 96 Zr(α,n) 99 Mo reaction have been analyzed in the statistical model (SM), complemented by the recently suggested pure barrier transmission model (PTBM) (Mohr et al 2020). In a schematic notation, the cross section of an α-induced (α,X) reaction is given by…”

“…The reason for the wide range of predictions was identified and discussed in Mohr et al (2020). The usual SM calculations show a dramatic sensitivity to the tail of the imaginary potential.…”

“…The usual SM calculations show a dramatic sensitivity to the tail of the imaginary potential. To avoid this sensitivity, an alternative approach was suggested in Mohr et al (2020) to use the PBTM model for the calculation of the total reaction cross section σ reac . The Supplement of Mohr et al (2020) provides the new ATOMKI-V2 αOMP which reproduces measured (α,n) cross sections over a wide range of masses and energies with deviations below a factor of two.…”

New measurement of the Sm144(α,γ)Gd148 reaction rate for the

“…See text for details. Recently, a new model for cross section predictions for α-induced reactions at low energies was proposed by Mohr et al [64][65][66]: the pure barrier transmission model (pBTM). For this model calculations are performed using the code CCFULL [67].…”

Constraining nucleosynthesis in neutrino-driven winds: observations, simulations and nuclear physics

“…In the present work, we build on the technique of Bliss et al (2020), using new, constrained rates of (α, xn) reactions, based on the Atomki-V2 αOMP (Mohr et al 2020). In addition, we compare for the first time our nuclear reaction impact study results with abundance observations of metal-poor stars with [Fe/H]<-1.5 that show an enhancement in their lighter heavy element distribution and are considered candidates for the weak rprocess.…”