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中子辐射俘获截面是核天体物理、核反应堆设计、核医学以及核技术应用等领域中所需的关键数据。目前，受制于实验技术上的困难，缺少半衰期短至数年或更短核素的中子辐射俘获截面测量数据。本文采用了一种间接测量短寿命核素反应截面的方法——替代反应法，在中国原子能科学研究院北京HI-13串列加速器上利用89Y (p,α)反应作为替代反应，产生与短寿命核素中子辐射俘获85Sr (n,γ)反应相同的复合核86Sr*进行替代反应法的实验研究。通过使用硅探测器组成的望远镜阵列与HPGe探测器阵列符合测量，得到了与特定能量角度的出射α粒子符合γ射线能谱，从而获得了不同激发能下复合核的γ衰变的概率。结合使用UNF唯象光学模型计算的复合核形成截面，得到了中子能量范围En=0.02~1.22 MeV的85Sr中子辐射俘获截面。并且，基于TALYS计算的自旋宇称分布，建立了修正模型用于补偿直接反应和替代反应中自旋-宇称布居的差异，改进了基于WeisskopfEwing近似下的间接测量结果。Neutron capture cross sections, as important parameters describing the probability of neutron-nucleus reactions, play a key role in multiple scientific fields. In astrophysics, neutron capture cross section data are essential elements for understanding stellar nucleosynthesis processes. In particular, in extreme environments such as supernova explosions and neutron star mergers, accurate neutron capture cross sections can reveal the secrets of heavy element formation. In the field of national security, neutron capture cross sections are crucial for the design of nuclear weapons and the security of nuclear materials. By accurately grasping the neutron capture characteristics of different nuclides, the nuclear reaction process can be optimized to ensure strategic security. In addition, in the simulation of nuclear power generation, neutron capture cross section data are the basis of reactor design and operational analysis. Through in-depth research and precise measurements of neutron capture cross sections, the safety and efficiency of nuclear reactors can be improved, promoting the sustainable development of nuclear energy. At present, there are few studies on neutron capture cross sections of nuclides with half-lives of only a few years or even shorter, mainly due to the complexity of measurement techniques and the instability of the nuclides themselves. The neutron capture cross section data of these nuclides are crucial for reactor design, nuclear medicine applications, and nuclear waste treatment. Further research requires the development of more advanced detection techniques and theoretical models to accurately measure and predict their neutron capture behavior.
The surrogate reaction method, as an effective measurement means, plays an important role in the research of reaction cross sections of short-lived nuclides. Its basic idea is to indirectly obtain the reaction cross section information of short-lived nuclides by measuring the specific particles emitted by stable nuclides. Specifically, when stable nuclides are bombarded by high-energy particles, nuclear reactions will occur and specific particles will be released. By accurately measuring the energy, angle, and number of these particles, the cross section of short-lived nuclides in the corresponding reaction can be inferred. This method can not only overcome the technical difficulties of direct measurement of short-lived nuclides, but also improve the accuracy and reliability of the measurement results, providing important support for nuclear physics research. In addition, the substitute reaction method also shows broad application prospects in the fields of nuclear technology application and nuclear data assessment.
The experiment was carried out on the Beijing HI-13 tandem accelerator at the China Institute of Atomic Energy. 89Y was bombarded with 22 MeV protons, and the 85Sr(n, γ) cross section was measured through the (p, αγ) reaction. The telescope array composed of silicon strip detectors can effectively identify the reaction products. By precisely measuring parameters such as the energy and angle of particles, the array can distinguish different nuclides, thus determining the outgoing particles. Combined with the γ-ray energy spectrum analysis of the HPGe detector, the (n, γ) reaction cross section data of 85Sr under the Weisskopf-Ewing (W-E) approximation were extracted. Due to the mismatch of the Jπ population between the existing alternative reactions and direct reactions, it is necessary to compensate for this mismatch and then correct the results. In order to obtain relatively reliable results, the Jπ population calculated by TALYS was used to revise the experimental data of the (n,γ) cross section.
The results show that the cross section of 85Sr(n, γ) varies with neutron energy in a specific energy range, which is consistent with the trend of the existing international evaluation library data, verifying the effectiveness of the alternative reaction method for cross section measurement. It provides an important experimental basis for further exploring the nuclear reaction mechanism and nuclear data application. This method has reference significance for the cross section measurement of other nuclides.-
Keywords:
- neutron-capture cross section /
- surrogate reaction method /
- short-lived radioactive nuclei
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