The competitive double-$\gamma$ decay of the $2_1{}^{+}$ state of an even-even spherical nucleus is studied for the first time. The coupling of one-, two-, and three-phonon terms in the wave functions of excited states is taken into account within the microscopic model based on the Skyrme energy density functional. The approach enables one to perform the calculations in very large configurational spaces. We estimate the generalized electric dipole polarizabilities involved in the $\gamma \gamma /\gamma$ decay process and make a prediction for the branching ratio of the competitive $\gamma \gamma$-decay relative to its single $\gamma$-decay calculated to be $3\times {10}^{-8}$ for the case of ${}^{48}\mathrm{Ca}$.

中文翻译：

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核21+态的γγ衰变宽度的首次计算：Ca48的情况

竞争激烈的双$\gamma$ 的衰败 $2_1{}^{+}$首次研究了偶偶球核的状态。在基于 Skyrme 能量密度泛函的微观模型中考虑了激发态波函数中一、二和三声子项的耦合。该方法使人们能够在非常大的配置空间中执行计算。我们估计了涉及的广义电偶极子极化率$\gamma \gamma /\gamma$ 衰变过程并预测竞争者的分支率 $\gamma \gamma$-相对于其单一的衰减 $\gamma$- 衰减计算为 $3\times {10}^{-8}$ 对于这种情况 ${}^{48}钙$.