Extraction of Gamow-Teller strength distributions from 56Ni and 55Co via the (p,n) reaction in inverse kinematics
Extraction of Gamow-Teller strength distributions from 56Ni and 55Co via the (p,n) reaction in inverse kinematics
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通过逆运动学中的 (p,n) 反应从 56Ni 和 55Co 中提取 Gamow-Teller 强度分布
DOI：
10.1103/physrevc.86.034324
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发表时间：
2012
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et al.,
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作者：
M. Sasano;H. Sakai;K. Yako;et al.,
背景：稳定和不稳定壳同位素的Gamow-Teller （GT）跃迁强度分布是估计恒星演化中重要的电子俘获率的关键输入。长期以来，中间束能量的电荷交换实验一直用于测试GT强度的理论预测，但以前的实验主要局限于稳定的原子核。由于大部分与天体物理应用相关的原子核（包括ni等关键原子核）是不稳定的，因此需要使用不稳定同位素进行逆运动学电荷交换实验的新方法。目的：对ni（）和co（）反应进行逆运动学测量，分别提取过渡到cu和ni的GT强度。利用KB3G和GXPF1J相互作用，将提取的强度分布与壳模型预测结果进行了比较。通过调用同位旋对称，这些强度分布分别与ni基态和ni到最终态inCo和co的电子捕获有关。方法：利用低能中子探测器阵列测量液氢靶反冲的中子，确定了ni（）和co（）反应的微分截面和激发能谱。利用多极分解分析提取了GT对光谱的贡献，并利用零线性动量传递时GT强度与微分截面之间的比例关系将其转换为强度。结果：从ni和co中提取的GT强度分别达到激发能8和15 MeV。与KB3G相互作用相比，在GXPF1J相互作用下的壳中进行的壳模型计算能更好地再现实验GT强度分布。结论：成功地建立了一种测量不稳定原子核上电荷交换反应的新方法。它可以用于研究不稳定核在任何质量区域的等矢量响应，以及超过粒子衰变阈值的激发能。在第一个实验中，研究了Ni（）和co（）反应，并提取了GT跃迁强度，目的是测试用于模拟晚期恒星演化中估计电子捕获速率的壳模型计算。采用GXPF1J相互作用的计算最能再现试验强度分布。
Background:Gamow-Teller (GT) transition strength distributions in stable and unstable-shell isotopes are key inputs for estimating electron-capture rates important for stellar evolution. Charge-exchange experiments at intermediate beam energies have long been used to test theoretical predictions for GT strengths, but previous experiments were largely restricted to stable nuclei. Since a large fraction of the nuclei relevant for astrophysical applications (including key nuclei such asNi) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes.Purpose:TheNi() andCo() reactions were measured in inverse kinematics in order to extract GT strengths for transitions toCu andNi, respectively. The extracted strength distributions were compared with shell-model predictions in theshell using the KB3G and GXPF1J interactions. By invoking isospin symmetry, these strength distributions are relevant for electron captures on the ground states ofNi andNi to final states inCo andCo, respectively.Method:Differential cross sections and excitation energy spectra for theNi() andCo() reactions were determined by measuring neutrons recoiling from a liquid hydrogen target into the Low Energy Neutron Detector Array. GT contributions to the spectra were extracted by using a multipole decomposition analysis and were converted to strengths by employing the proportionality between GT strength and differential cross section at zero linear momentum transfer.Results:GT strengths fromNi andCo were extracted up to excitation energies of 8 and 15 MeV, respectively. Shell-model calculations performed in theshell with the GXPF1J interaction reproduced the experimental GT strength distributions better than calculations with the KB3G interaction.Conclusions:A new technique for measuring () charge-exchange reactions on unstable nuclei was successfully developed. It can be used to study the isovector response of unstable nuclei in any mass region and for excitation energies beyond the particle decay threshold. In the first experiment,Ni() andCo() reactions were studied and GT transition strengths were extracted for the purpose of testing shell-model calculations used to estimate electron-capture rates in simulations of late stellar evolution. The calculation using the GXPF1J interaction was found to best reproduce the experimental strength distribution.