Cross section of α -induced reactions on Au197 at sub-Coulomb energies

Abstract

Background: Statistical model calculations have to be used for the determination of reaction rates in large-scale reaction networks for heavy-element nucleosynthesis. A basic ingredient of such a calculation is the α-nucleus optical model potential. Several different parameter sets are available in literature, but their predictions of α-induced reaction rates vary widely, sometimes even exceeding one order of magnitude.Purpose: This paper presents the result of α-induced reaction cross-section measurements on gold which could be carried out for the first time very close to the astrophysically relevant energy region. The new experimental data are used to test statistical model predictions and to constrain the α-nucleus optical model potential.Method: For the measurements the activation technique was used. The cross section of the (α,n) and (α,2n) reactions was determined from γ-ray counting, while that of the radiative capture was determined via X-ray counting. Results:The cross section of the reactions was measured below Eα = 20.0 MeV. In the case of the 197 Au(α,2n) 199 Tl reaction down to 17.5 MeV with 0.5-MeV steps, reaching closer to the reaction threshold than ever before. The cross section of 197 Au(α,n) 200 Tl and 197 Au(α,γ) 201 Tl was measured down to Eα = 13.6 and 14.0 MeV, respectively, with 0.5-MeV steps above the (α,2n) reaction threshold and with 1.0-MeV steps below that. Conclusions:The new dataset is in agreement with the available values from the literature, but is more precise and extends towards lower energies. Two orders of magnitude lower cross sections were successfully measured than in previous experiments which used γ-ray counting only, thus providing experimental data at lower energies than ever before. The new precision dataset allows us to find the best-fit α-nucleus optical model potential and to predict cross sections in the Gamow window with smaller uncertainties.

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

“…[62], the multiplication of the real part of the Demetriou #3 potential by factors between 1.1 and 1.3 has been very successful in describing (α, n) cross sections over a wide mass range of target nuclei. This finding has also been supported by the recent measurements of α-induced reaction cross sections on 197 Au [63]. In this measurement, a scaling of the real part of the Demetriou #3 potential did not yield any satisfying results.…”

“…In contrast to Ref. [63] which used a brute-force-like method to search for the best combination of input parameters, we are relying on a Bayesian optimization [68] of nuclear input parameters, which we also recently applied to investigate the γ -ray strength function in 94 Mo [69].…”

Stable beam experiments in wide energy ranges serving low energy nuclear astrophysics

“…3.3. The 14 N(p,γ) 15 O reaction The 14 N(p,γ) 15 O reaction is another key reaction of nuclear astrophysics as this reaction determines the rate of the CNO cycle hydrogen burning in various astrophysical sites. In spite of the tremendous experimental effort devoted to this reaction, the knowledge of its reaction rate still remains poor compared to the requirements of astrophysical models motivated by high precision observations [10].…”

“…In spite of the tremendous experimental effort devoted to this reaction, the knowledge of its reaction rate still remains poor compared to the requirements of astrophysical models motivated by high precision observations [10]. Owing probably to the short half-life of 15 O (t 1/2 = 2.0 min), no modern measurement of the 14 N(p,γ) 15 O has been carried with the activation technique. Therefore, the aim of our ongoing project at Atomki is to provide activation cross section data which are in many aspects independent from the in-beam γ-spectroscopy data sets.…”

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

“…Next, this simple model is combined with a carefully chosen AOMP, and total αþ nucleus reaction cross sections are calculated at low energies, thus enabling the prediction of α-induced reaction rates for heavy target nuclei with significantly reduced uncertainties. As a first example, α-induced reactions for 197 Au were chosen because a recent experiment has provided high-precision data down to energies close to the Gamow window [11]. Then, predictions of α-induced cross sections for several heavy targets (above A ¼ 150) are compared to experimental data from literature.…”