During nuclear fission, a heavy nucleus splits into two rotating fragments. The associated angular momentum is large, yet the mechanism of its generation and its dependence on the mass of fragments remain poorly understood. In this Letter, we provide the first microscopic calculations of angular-momentum distributions in fission fragments for a wide range of fragment masses. For the benchmark case of ${}^{239}\mathrm{Pu}(n_{\text{th}},f)$, we find that the angular momentum of the fragments is largely determined by the nuclear shell structure and deformation, and that the heavy fragments therefore typically carry less angular momentum than their light partners. We use the fission model freya to simulate the emission of neutrons and photons from the fragments. The dependence of the angular momenta on fragment mass after the emission of neutrons and statistical photons is linear for the heavy fragments and either constant or weakly linear for the light fragments, consistent with the universal sawtooth pattern suggested by recent experimental data. Finally, we observe that using microscopic angular-momentum distributions modifies the number of emitted photons significantly.

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从微观理论看裂变碎片的角动量

在核裂变过程中，一个重核分裂成两个旋转的碎片。相关的角动量很大，但其产生机制及其对碎片质量的依赖仍然知之甚少。在这封信中，我们提供了裂变碎片角动量分布的第一次微观计算，适用于各种碎片质量。对于基准案例${}^{239}浦(n_{\text{日}},F)$，我们发现碎片的角动量在很大程度上取决于核壳结构和变形，因此重碎片通常比轻碎片携带的角动量更少。我们使用裂变模型freya来模拟来自碎片的中子和光子的发射。中子和统计光子发射后角动量对碎片质量的依赖性对于重碎片是线性的，对于轻碎片是恒定的或弱线性的，与最近的实验数据表明的通用锯齿模式一致。最后，我们观察到使用微观角动量分布显着修改了发射光子的数量。