Measurements of ¹⁶⁰Dy (p, γ) at Energies Relevant for the Astrophysical γ Process

Abstract

Rare information on photodisintegration reactions of nuclei with mass numbers A ≈ 160 at astrophysical conditions impedes our understanding of the origin of p-nuclei. Experimental determination of the key (p, γ) cross sections has been playing an important role in verifying nuclear reaction models and providing rates of relevant (γ, p) reactions in the γ process. In this paper we report the first cross-section measurements of 160Dy(p, γ)161Ho and 161Dy(p, n)161Ho in the beam energy range of 3.4–7.0 MeV, partially covering the Gamow window. Such determinations are possible by using two targets with various isotopic fractions. The cross-section data can put a strong constraint on the nuclear level densities and gamma strength functions for A ≈ 160 in the Hauser–Feshbach statistical model. Furthermore, we find the best parameters for TALYS that reproduce the available A ∼ 160 data, 160Dy(p, γ)161Ho and 162Er(p, γ)163Tm, and recommend the constrained 161Ho(γ, p)160Dy reaction rates over a wide temperature range for γ process network calculations. Although the determined 161Ho(γ, p) stellar reaction rates at the temperature of 1 to 2 GK can differ by up to one order of magnitude from the NON-SMOKER predictions, it has a minor effect on the yields of 160Dy and accordingly the p-nuclei, 156,158Dy. A sensitivity study confirms that the cross section of 160Dy(p, γ)161Ho is measured precisely enough to predict yields of p nuclei in the γ process.

The origin of low-abundance neutron-deficient stable isotopes and the relevant cross section measurements

“…这一方法已在天体物理能区成功测量了 130 Ba(p, γ) 131 La [62] 、 152 Gd(p, γ) 153 Tb [63] 以及 162 Er(p, γ) 163 Er [64] 、 160 Dy (p, γ) 161 Er [65] 等反应截面.…”

“…2014 年，Quinn 等人首次利用 γ 求和技术对逆动力学开展了测量 [75] . 的实验截面测量 [65] ，探索 A≈160 核区产生因子相对于 16 为提取 160 Dy(p, γ) 161 Ho 反应截面，选用了两种不同丰度的镝同位素靶。我们团队在中国 原子能科学研究院 2×1.7 MeV 及 H1-13 的串列加速器装置上完成了实验，设计了具有法拉第 筒功能的真空靶室，发展了实时亚微安级束流强度的采样方法，在低本底屏蔽系统中，通过 高精度测量目标产物核的特征伽马射线 [81] ，首次提取了 3.4~7.0 MeV 能量下 160 Dy(p, γ) 161 Ho、 161 Dy(p, n) 161 Ho 的反应截面 [65] . 数的 TALYS(虚线)所预言的反应截面进行比较 [65] .…”

“…阴影区域代表(p, γ)的相关 Gamow 窗口. , and the TALYS(dashed line) codes using their default parameters [65] 国内已经逐步开展了针对 p-核相关的实验研究，并取得了较好的进展 [53,65] 参考文献 involve the target ground state only, so that a correction factor, called the stellar enhancement factor, has to be applied to the laboratory data in order to account for the possible contribution of the target excited states to the stellar capture rates.…”

“…Figure 7 Measured cross sections of the 160 Dy(p, γ) 161 Ho (solid squares) and 161 Dy(p, n) 161 Ho (open squares) reactions compared with the predictions by the NON-SMOKER(solid line), EMPIRE(dotted line), and the TALYS(dashed line) codes using their default parameters[65] . The relevant Gamow…”