147 Sm +n共振的自旋测量：非统计效应的进一步证据
Spin measurements for 147Sm+n resonances: Further evidence for non-statistical effects
摘要：
通过测量中子俘获后γ射线级联的多重性，确定了~（147）Sm（n，γ）反应中共振态的自旋J。使用这种技术，我们能够确定所有的J值，但14的140个已知的共振低于En = 1千电子伏，包括41个公司J分配的共振，其自旋以前是未知的或暂定的。这些新的自旋分配，连同先前确定的共振参数，使我们能够提取单独的能级间距和中子强度函数为J = 3和4共振。此外，一些统计测试的数据表明，很少有共振的任何自旋已错过低于En = 700 eV。由于最近从147 Sm（n，alpha）数据的分析中报道了En = 350 eV附近的非统计效应，因此我们将数据分为两个区域：0 < En < 350 eV和350 < En < 700 eV。使用中子宽度从以前的测量和公布的技术，用于校正错过的共振和测试数据是否与波特-托马斯分布一致，我们发现，减少中子宽度分布低于350 eV的共振是符合预期的波特-托马斯分布。另一方面，我们发现，在350 < En < 700 eV区域的约化中子宽度数据与波特-托马斯分布不一致，但与具有两个或更多个自由度的卡方分布非常一致。我们讨论了可能的解释，这些观察到的非统计效应和它们可能与以前在其他核素中观察到的类似效应。
英文摘要：
We have determined the spins J of resonances in the 147Sm(n,gamma) reaction by measuring multiplicities of gamma-ray cascades following neutron capture. Using this technique, we were able to determine J values for all but 14 of the 140 known resonances below En = 1 keV, including 41 firm J assignments for resonances whose spins previously were either unknown or tentative. These new spin assignments, together with previously determined resonance parameters, allowed us to extract separate level spacings and neutron strength functions for J = 3 and 4 resonances. Furthermore, several statistical test of the data indicate that very few resonances of either spin have been missed below En = 700eV. Because a non-statistical effect recently was reported near En = 350 eV from an analysis of 147Sm(n,alpha) data, we divided the data into two regions; 0 < En < 350 eV and 350 < En < 700 eV. Using neutron widths from a previous measurement and published techniques for correcting for missed resonances and for testing whether data are consistent with a Porter-Thomas distribution, we found that the reduced-neutron-width distribution for resonances below 350 eV is consistent with the expected Porter-Thomas distribution. On the other hand, we found that reduced-neutron-width data in the 350 < En < 700 eV region are inconsistent with a Porter-Thomas distribution, but in good agreement with a chi-squared distribution having two or more degrees of freedom. We discuss possible explanations for these observed non-statistical effects and their possible relation to similar effects previously observed in other nuclides.
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