Iron-60 and aluminium-26 are unique chemical isotopes produced by stellar nucleosynthesis in our Galaxy and beyond. The ratio of these isotopes is a key parameter in understanding stellar evolution, but there is a known discrepancy between the value obtained from gamma-ray telescopes and that predicted by supernova models. Recently Artemis Spyrou and colleagues reported a cross-section of the neutron-capture rate of ⁵⁹Fe that is higher than previously thought, implying an enhanced yield of ⁶⁰Fe in massive stars, which further exacerbates the discrepancy.

In their experiment, excited iron was produced from the beta-decay of the radioactive manganese isotope (⁶⁰Mn) in order to extract its nuclear level density and gamma-ray strength function using the β-Oslo method. The nuclear level density gives the number of energy levels per unit energy as a function of excitation energy, spin, and parity and its normalization is used to fix the slope of the gamma-ray strength function, which is related to the probability of gamma-ray emission at a particular energy and multipolarity. Combined with theoretical calculations, they showed that at lower energy the gamma-ray strength function is increased. This low-energy feature is the main reason for the difference in nuclear reaction cross-section and isotope ratio between previous works and this study.

铁 60 和铝 26 是银河系及更远地区恒星核合成产生的独特化学同位素。这些同位素的比率是理解恒星演化的一个关键参数，但从伽马射线望远镜获得的值与超新星模型预测的值之间存在已知差异。最近，Artemis Spyrou 及其同事报告了 ⁵⁹Fe 的中子俘获率的横截面，这比以前认为的要高，这意味着大质量恒星的产额增加了 ⁶⁰Fe，这进一步加剧了这种差异。

在他们的实验中，放射性锰同位素 （⁶⁰Mn） 的 β 衰变产生了激发铁，以便使用 β-Oslo 方法提取其核能级密度和伽马射线强度函数。核能级密度给出了每单位能量的能级数作为激发能、自旋和奇偶性的函数，其归一化用于固定伽马射线强度函数的斜率，该斜率与特定能量和多极性下伽马射线发射的概率有关。结合理论计算，他们表明，在较低能量下，伽马射线强度函数会增加。这种低能特性是前人与本研究核反应截面和同位素比值存在差异的主要原因。