Approaching the Gamow Window with Stored Ions: Direct Measurement of Xe124(p,γ

Abstract

We report the first measurement of low-energy proton-capture cross sections of 124 Xe in a heavyion storage ring. 124 Xe 54+ ions of five different beam energies between 5.5 AMeV and 8 AMeV were stored to collide with a windowless hydrogen target. The 125 Cs reaction products were directly detected. The interaction energies are located on the high energy tail of the Gamow window for hot, explosive scenarios such as supernovae and X-ray binaries. The results serve as an important test of predicted astrophysical reaction rates in this mass range. Good agreement in the prediction of the astrophysically important proton width at low energy is found, with only a 30% difference between measurement and theory. Larger deviations are found above the neutron emission threshold, where also neutron-and γ-widths significantly impact the cross sections. The newly established experimental method is a very powerful tool to investigate nuclear reactions on rare ion beams at low center-of-mass energies.Charged-particle induced reactions like (p,γ) and (α,γ) and their reverse reactions play a central role in the quantitative description of explosive scenarios like supernovae [1] or X-ray binaries [2], where temperatures above 1 GK can be reached. The energy interval in which the reactions most likely occur under astrophysical conditions is called the Gamow window [3,4]. Experimentalists usually face two major challenges when approaching the Gamow window: firstly, the relatively low center-of-mass energies of only a few MeV or less, and secondly, the rapid decrease of cross sections with energy. The high stopping power connected to low-energy beams typically limits the amount of target material, and thus the achievable luminosity. A measurement of small cross sections, on the contrary, requires high luminosities.The description of charged-particle processes in explosive nucleosynthesis -e.g., the γ process occurring in core-collapse and thermonuclear supernovae [5-7] and the rp process on the surface of mass-accreting neutron stars [8] -requires large reaction networks including very short-lived nuclei. Experimental data are extremely scarce [9], especially in the mass region A > 70, and the modelling relies on calculated cross sections. It is therefore essential to test the theory and its central input parameters. In this Letter we report the first study of the 124 Xe(p,γ) 125 Cs reaction. The cross section is measured on the high energy tail of the Gamow peak, which is located between 2.74 and 5.42 MeV at 3.5 GK in the γ process [4]. While the 124 Xe(p,γ) reaction serves as a major milestone for improving the experimental technique

Progress on internal gas-jet target nuclear reaction at the HIRFL-CSR

“…EXL合作 组发展出了重离子储存环适用的硅探测器 [19] , 利用硅 探测器进行了超高真空差分隔离 [20] , 发展了储存环气 体内靶核反应实验技术 [18] . 在这些技术支撑下, 开展了 广泛的实验研究, 例如, 利用质子和α两种轻粒子的弹 性散射开展了原子核核物质密度分布半径的测量实 验 [21,22] , 基于α粒子在原子核上的非弹性散射研究了巨 共振 [10] , 在低能区直接测量了核天体物理相关的质子 俘获(p, γ)截面 [15,16] , 以及利用(p, d)转移反应尝试测量 了核天体物理相关的能态信息 [23] . EXL合作组取得的 这些成果展示出了储存环气体内靶核反应作为一个新 实验方式的独特之处.…”

Employing $p+^{58}$Ni elastic scattering for determination of $K$-shell ionization cross section of $^{58}$Ni$^{19+}$ in collisions with hydrogen gas target at 95 MeV/u

“…Consequently, only a precision of about 30% could be reached for absolute ionization cross section measurements [4,13]. This experimental precision is lower than a precision of a few percent for theoretical predictions on atomic cross sections [14,15]. The experimental challenge was also noted in the review paper [13].…”

“…Compared to strong interaction, electromagnetic interaction is well studied. Thus, theoretical atomic cross sections are often used to normalize less-accurately known nuclear reaction cross sections in nuclear reaction experiments [14,16]. Many in-ring nuclear reaction experiments have been performed at the ESR ring [14,16,17,18,19].…”

“…Thus, theoretical atomic cross sections are often used to normalize less-accurately known nuclear reaction cross sections in nuclear reaction experiments [14,16]. Many in-ring nuclear reaction experiments have been performed at the ESR ring [14,16,17,18,19]. In a pilot in-ring 58 Ni(p, p) 58 Ni elastic scattering experiment at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) [20], in order to show a potential for extracting optical model potentials (OMPs) of unstable nuclei, a theoretical K-shell ionization cross section was applied to determine the reaction luminosity.…”

Radiative electron capture as a tunable source of highly linearly polarized x rays

“…Based on all these studies, REC in collisions with open K-and L-shell ions and light target atoms appears to be well described by theory with respect to total as well as angular differential cross sections. Consequently, this process has meanwhile been established for normalization purposes of experimental data in the realm of atomic and nuclear physics [17][18][19]. A further important aspect of REC are the linear polarization properties of REC radiation, which has already been a subject of detailed theoretical investigations [20][21][22].…”