原子核Gamow-Teller共振和β衰变寿命的超越平均场描述

Beyond Mean-field Description of Nuclear Gamow-Teller Resonance and β-decay Half-lives

原子核的β衰变是决定宇宙中从铁到铀重元素合成的关键核过程之一。原子核β衰变的主导核跃迁是Gamow-Teller(GT)跃迁,因此,研究原子核β衰变寿命的关键是准确描述原子核的GT跃迁。描述原子核GT跃迁和β衰变寿命最常用的理论模型之一为无规相位近似(RPA)模型。然而,由于该模型仅考虑了一粒子一空穴激发组态,因此无法给出GT共振宽度,并容易高估β衰变寿命。为了克服上述困难,基于Skyrme密度泛函,发展了包含粒子振动耦合效应的无规相位近似(RPA+PVC)模型。相比于RPA模型,该模型在组态空间进一步考虑了一粒子一空穴和声子的耦合组态,从而包含了超越平均场的多体关联效应。为了推广至开壳原子核的研究,进一步考虑了对关联效应,发展了包含准粒子振动耦合效应的准粒子无规相位近似(QRPA+QPVC)模型。基于上述模型,研究了幻数原子核和超流原子核的GT跃迁、β衰变和β^(+)/电子俘获。研究发现,采用同一组Skyrme相互作用参数SkM^(*),上述模型能够重现实验测量的GT共振宽度和跃迁强度分布,部分解释实验观测的GT跃迁强度压低问题,并同时改进对β衰变寿命的描述。该文针对上述最新研究进展进行了综述,并对将来的发展方向给出展望。

Nuclear β decay is one of the key nuclear processes that determine how the heavy elements from Fe to U in the universe were made.The dominant nuclear process in β-decay is the Gamow-Teller(GT) transition,so the key point for nuclear β-decay study is to describe nuclear GT transition accurately.One of the most widely used nuclear model is random phase approximation(RPA).However,since it only includes one-particle one-hole excitation configurations,this model cannot describe spreading width of GT resonance,and tends to overestimate the β-decay half-lives.To overcome these difficulties,based on Skyrme density functional,the random phase approximation with particle vibration coupling(RPA+PVC) model was developed.Compared to RPA model,it further includes the one-particle one-hole coupled with phonons in its configuration space,which includes many-body correlations beyond mean field approximation.To extend the study to open shell nuclei,the quasiparticle random phase approximation with quasiparticle vibration coupling model(QRPA+QPVC),which includes pairing correlations,was developed.Based on the above models,the GT excitation,β decay,β^(+)/EC of magic nuclei and superfluid nuclei were studied.It is found that with the same Skyrme interaction SkM^(*),the experimental GT width and transition strength profile were well reproduced,the quenching phenomenon was partly explained,and the description ofβ-decay half-lives were improved at the same time.The recent progress of this study is reviewed,and in the meantime the perspectives for future developments are given.