arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 0809.2762nucl-ex
收藏

中子俘获中的非统计效应

Non-Statistical Effects in Neutron Capture

P. E. Koehler, T. A. Bredeweg, K. H. Guber, J. A. Harvey, J. M. ODonnell, R. Reifarth, R. S. Rundberg, J. L. Ullmann, D. J. Vieira, D. Wiarda, J. M. Wouters

摘要:

关于中子俘获测量中的非统计效应已有许多报道。然而,约化中子宽度分布偏离预期的波特-托马斯(PT)形状的报道在很大程度上被忽略了。大多数这些偏差已被报道为奇A核素。由于这些核素的大多数共振都没有可靠的自旋(J)分配,因此报告的PT偏差可能是由于不正确的J分配。最近,我们发展了一种新的方法来测量自旋的中子共振使用的DANCE探测器在LANSCE。用147 Sm样品进行的测量使我们能够确定几乎所有已知的低于1千电子伏的共振自旋。此外,对这些数据的分析表明,约化中子宽度分布与PT在低于350 eV的共振下很好地一致,但与PT在350和700 eV之间的共振不一致。我们以前的(n,α)测量表明,α强度函数在这个能量下也会突然变化。目前还没有已知的解释来解释这两种非统计效应。最近,我们发展了另一种新的方法来确定中子共振的自旋。为了实现这项技术,需要对一个简单得多的设备做一个小的改变(记录符合事件的脉冲高度信息):一对C6 D 6伽马射线探测器,我们已经在ORELA使用多年来测量中子俘获截面。对95 Mo样品的测量表明,该方法不仅可以很好地确定自旋,而且还可以进行宇称分配。总之,这些新技术在LANSCE和ORELA可能是非常有用的非统计效应的进一步说明。

英文摘要:

There have been many reports of non-statistical effects in neutron-capture measurements. However, reports of deviations of reduced-neutron-width distributions from the expected Porter-Thomas (PT) shape largely have been ignored. Most of these deviations have been reported for odd-A nuclides. Because reliable spin (J) assignments have been absent for most resonances for such nuclides, it is possible that reported deviations from PT might be due to incorrect J assignments. We recently developed a new method for measuring spins of neutron resonances by using the DANCE detector at LANSCE. Measurements made with a 147Sm sample allowed us to determine spins of almost all known resonances below 1 keV. Furthermore, analysis of these data revealed that the reduced-neutron-width distribution was in good agreement with PT for resonances below 350 eV, but in disagreement with PT for resonances between 350 and 700 eV. Our previous (n,alpha) measurements had revealed that the alpha strength function also changes abruptly at this energy. There currently is no known explanation for these two non-statistical effects. Recently, we have developed another new method for determining the spins of neutron resonances. To implement this technique required a small change (to record pulse-height information for coincidence events) to a much simpler apparatus: A pair of C6D6 gamma-ray detectors which we have employed for many years to measure neutron-capture cross sections at ORELA. Measurements with a 95Mo sample revealed that not only does the method work very well for determining spins, but it also makes possible parity assignments. Taken together, these new techniques at LANSCE and ORELA could be very useful for further elucidation of non-statistical effects.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑