The radiative neutron capture rates for isotopes of astrophysical interest are commonly calculated within the statistical Hauser–Feshbach reaction model. Such an approach, assuming a high level density in the compound system, can be questioned in light and neutron-rich nuclei for which only a few or no resonant states are available. Therefore, in this work we focus on the direct neutron-capture process. We employ a shell-model approach in several model spaces with well-established effective interactions to calculate spectra and spectroscopic factors in a set of 50 neutron-rich target nuclei in different mass regions, including doubly-, semi-magic and deformed ones. Those theoretical energies and spectroscopic factors are used to evaluate direct neutron capture rates and to test global theoretical models using average spectroscopic factors and level densities based on the Hartree–Fock–Bogoliubov plus combinatorial method. The comparison of shell-model and global model results reveals several discrepancies that can be related to problems in level densities. All the results show however that the direct capture is non-negligible with respect to the by-default Hauser–Feshbach predictions and can be even 100 times more important for the most neutron-rich nuclei close to the neutron drip line.

通常在统计的Hauser-Feshbach反应模型中计算对天文学感兴趣的同位素的辐射中子捕获率。假设在复合系统中具有高能级密度，这种方法可能会在光和富含中子的原子核中受到质疑，因为它们只有很少的共振态或没有共振态。因此，在这项工作中，我们专注于直接中子捕获过程。我们在具有良好建立的有效相互作用的几个模型空间中采用壳模型方法，以计算在不同质量区域（包括双，半魔术和变形）中的一组50个富中子目标核的光谱和光谱因子。这些理论能量和光谱因子用于评估直接中子捕获率，并基于Hartree-Fock-Bogoliubov加组合方法，使用平均光谱因子和能级密度测试整体理论模型。壳模型和全局模型结果的比较揭示了一些与级别密度问题有关的差异。然而，所有结果表明，相对于默认的Hauser–Feshbach预测，直接捕获是不可忽略的，对于接近中子滴线的最富中子核而言，直接捕获甚至可能重要100倍。