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arXiv 2108.04347nucl-thnucl-ex
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在fission碎片衰变期间通过中子和$γ$射线发射的Angular momentum去除

Angular momentum removal by neutron and $γ$-ray emissions during fission fragment decays

I. Stetcu, A. E. Lovell, P. Talou, T. Kawano, S. Marin, S. A. Pozzi, A. Bulgac

备注：
9 pages, 6 figures; version accepted for publication
发表信息：
Phys. Rev. Lett. 127, 222502 (2021)
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摘要：

我们研究了通过中子和$γ$ -射线发射从裂变碎片（FF）中去除角动量，我们发现大约一半的中子是以角动量$\ge 1.5\hbar$发射的，并且中子和统计$γ$射线发射后角动量的变化是显著的，与通常的假设相矛盾。在我们的模拟中，每个裂变事件，中子和统计$γ$射线辐射改变碎片的自旋3.5 - 5~ $\hbar$，具有与平均值相当的大的标准偏差。这样宽的角动量去除分布可以隐藏裂变碎片初始自旋值中的任何潜在相关性。在我们的模型中，我们再现了中子发射后的离散跃迁的自旋测量数据，特别是在光FF的情况下。如果从分析中去除会产生同分异构态的事件，则对于重碎片的一致性进一步提高。最后，我们表明，虽然在我们的模型中的初始FF自旋不遵循最近的测量中观察到的锯齿状行为，中子和统计$γ$排放后计算的平均FF自旋呈现出类似于锯齿的形状。这表明，统计发射后测得的平均FF自旋不一定与前面暗示的断裂机制有关。

英文摘要：

We investigate the angular momentum removal from fission fragments (FFs) through neutron and $γ$-ray emission, where we find that about half the neutrons are emitted with angular momenta $\ge 1.5\hbar$ and that the change in angular momentum after the emission of neutrons and statistical $γ$ rays is significant, contradicting usual assumptions. Per fission event, in our simulations, the neutron and statistical $γ$-ray emissions change the spin of the fragment by 3.5 -- 5~$\hbar$, with a large standard deviation comparable to the average value. Such wide angular momentum removal distributions can hide any underlying correlations in the fission fragment initial spin values. Within our model, we reproduce data on spin measurements from discrete transitions after neutron emissions, especially in the case of light FFs. The agreement further improves for the heavy fragments if one removes from the analysis the events that would produce isomeric states. Finally, we show that while in our model the initial FF spins do not follow a saw-tooth like behavior observed in recent measurements, the average FF spin computed after neutron and statistical $γ$ emissions exhibits a shape that resembles a saw tooth. This suggests that the average FF spin measured after statistical emissions is not necessarily connected with the scission mechanism as previously implied.

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