Direct measurement of the astrophysical 93Nb(n,γ)94Nb reaction rate at the CSNS Back-n

The cross section of the 93Nb(n,γ) reaction plays a crucial role in the s-process nucleosynthesis, the retrospective dosimetry of nuclear reactors, and the classification of nuclear waste. The neutron capture cross section of 93Nb was measured by the time-of-flight method in the energy range of 10 eV to 1000 keV at the Back-n facility of the Chinese Spallation Neutron Source. In the resolved resonance region, the data reported multiple new resonance structures for the first time, including peaks at 966, 973, 1411, 2252, and 2284 eV, which are not present in existing evaluated libraries. By utilizing a high-purity target and a Bayesian-based double-bunch unfolding algorithm, this work successfully clarified several historical discrepancies. Specifically, the spurious structures caused by 181Ta impurities and the pseudo-doublet artifacts observed in previous measurements were effectively identified and resolved. Maxwellian-averaged cross sections were calculated within the temperature range of the s-process nucleosynthesis model (kT=5-100 keV). Astrophysical reaction rates were derived from the reaction cross section, and these rates differ from those in current datasets. This study provides a reliable benchmark for nuclear data evaluation and lays a solid foundation for optimizing nuclear energy applications and constraining astrophysical models.

93Nb(n,γ)反应截面在s过程（s-process）核合成、核反应堆回顾性剂量学以及核废物分类领域发挥着关键作用。本研究在中国散裂中子源（Chinese Spallation Neutron Source）的Back-n装置上，采用飞行时间法（time-of-flight method）测量了10 eV至1000 keV能区的93Nb中子俘获截面。在已分辨共振区，本测量数据首次报道了多个全新的共振结构，包括966 eV、973 eV、1411 eV、2252 eV与2284 eV处的共振峰，上述结构在现有核数据评价库中均未收录。本研究通过使用高纯度靶材与基于贝叶斯（Bayesian）的双束解卷算法（double-bunch unfolding algorithm），成功澄清了多项历史遗留的测量分歧。具体而言，此前测量中由181Ta杂质引发的虚假共振结构，以及观测到的伪双峰伪影，均被本研究有效识别并解决。本研究在s过程核合成模型的温度区间（kT=5~100 keV）内，计算了麦克斯韦平均截面（Maxwellian-averaged cross sections）。基于该反应截面，本研究推导得到天体物理反应率，且该反应率与当前公开数据集的结果存在差异。本研究为核数据评价提供了可靠的基准参照，同时为优化核能应用、约束天体物理模型奠定了坚实基础。