论文标题
降低核水平密度远离$β$稳定线的证据
Evidence for the reduction of nuclear level density away from the $β$-stability line
论文作者
论文摘要
通过分析激发$^{116} $ sn和$^{116} $ te nuclei的蒸发中子的光谱，已经研究了核水平密度的同胞依赖性。这些核是通过$ p $ + $^{115} $ in和$^{4} $ he + $^{112} $ sn反应在18-26 meV的激发能范围内的。由于兴奋能量低，中子光谱主要由第一次杂技衰减导致$β$稳定的$^{115} $ sn和中子缺陷的$^{115} $ te作为两种情况的残留物。实验光谱的理论分析已经在豪瑟 - 菲什巴赫形式主义中进行了，采用了水平密度参数的不同模型。可以观察到数据只能通过当质子数偏离$β$稳定值时单调降低的水平密度参数来解释。还通过使用木 - 撒克逊平均场进行微观壳模型计算来证实这一点。结果对不稳定核的水平密度的估计以及与$ r $ $ - 和$ rp $ - 过程相关的天体物理反应速率的计算具有很大的意义。
The isospin dependence of nuclear level density has been investigated by analyzing the spectra of evaporated neutrons from excited $^{116}$Sn and $^{116}$Te nuclei. These nuclei are populated via $p$ + $^{115}$In and $^{4}$He + $^{112}$Sn reactions in the excitation energy range of 18 - 26 MeV. Because of low excitation energy, the neutron spectra are predominantly contributed by the first-chance decay leading to the $β$-stable $^{115}$Sn and neutron-deficient $^{115}$Te as residues for the two cases. Theoretical analysis of the experimental spectra have been performed within the Hauser-Feshbach formalism by employing different models of the level density parameter. It is observed that the data could only be explained by the level density parameter that decreases monotonically when the proton number deviates from the $β$-stable value. This is also confirmed by performing a microscopic shell-model calculation with the Wood-Saxon mean field. The results have strong implication on the estimation of the level density of unstable nuclei, and calculation of astrophysical reaction rates relevant to $r$- and $rp$-processes.
