Threshold Effects in Neutron Elastic Scattering
Threshold Effects in Neutron Elastic Scattering
复制标题
中子弹性散射的阈值效应
DOI：
10.1103/physrev.131.1644
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发表时间：
1963
期刊：
影响因子：
--
通讯作者：
W. E. Meyerhof
中科院分区：
文献类型：
--
作者：
J. Wells;A. B. Tucker;W. E. Meyerhof
为了观察非弹性阈值附近中子弹性散射中的Wigner-cusp现象，测量了Li，Fe，Zr，Ba和Ce在这些元素的优势同位素激发第一激发态的阈值能量附近的微分弹性散射截面和全散射截面。研究的能量区域在阈值的两侧延伸约300千电子伏。成功地分析所观察到的尖点现象可以提供关于激发态自旋和宇称的信息。此外，在能量平均的Wigner-cusp理论原则上适用的中子能量和原子序数区域中是否存在低于阈值的效应可以给出相互作用机制的指示，即，直接相互作用或形成复合核。在本工作中，通过考虑更一般的角动量情况和微分弹性截面的显式尖点表达式，补充了Wigner尖点和能量平均Wigner尖点理论。尖点预测给出的系数展开的横截面成一系列的勒让德多项式。这种形式便于理论和实验的比较。在Li和Fe的弹性截面和总截面的非弹性阈值处观察到不寻常的特征。在这里，人们期望更多»注意到低于和高于维格纳尖点的阈值效应特征。然而，在这些情况下，对实验结果的解释并不是明确的-在Li中，因为预测的尖点效应太小，在本实验中无法观察到，而在Fe中，因为横截面的共振结构掩盖了预期的尖点效应。下降，开始在非弹性阈值，观察到在弹性截面的Ce，Ba和Zr。用能量平均的Wigner-cusps理论分析这种效应，理论与实验符合得很好。（auth）«少
In an attempt to observe the Wigner-cusp phenomenon in neutron elastic scattering near inelastic thresholds, the differential elastic and total cross sections of Li, Fe, Zr, Ba, and Ce near the threshold energy for exciting the firstexcited stutes of the dominant isotopes of these elements were measured. The energy region investigated extended approximately 300 kev on either side of threshold. Successful analysis of observed cusp phenomena can provide information on the spin and parity of excited stutes. In addition, the presence or absence of below-threshold effects in regions of neutron energy and atomic number where energy-averaged'' Wigner-cusp theory applies in principle can give an indication of the interaction mechanism, i.e., direct interaction or compound nucleus formation. The theory of Wigner cusps and energy-averaged'' Wigner cusps is supplemented in the present work by a consideration of slightiy more general angular-momentum situations and by explicit cusp expressions for differential-elastic cross sections. Cusp predictions are given in terms of the coefficients for expansion of the cross sections into a series of Legendre polynomials. This form facilitates comparison of theory and experiment. Unusual features were observed at the inelastic thresholds in the elastic and total cross sections of Li and Fe. Here one expectsmore » to notice a below, as well as above, threshold effect characteristic of Wigner cusps. In these cases, however, the interpretation of the experimental results is not unambigaous -in Li because the predicted cusp effect is too small to be observable in the present experiment and in Fe because the resonance structure of the cross sections overshadows the expected cusp effect. A drop, commencing at inelastic thresholds, is observed in the elastic cross sections of Ce, Ba, and Zr. Analysis of this effect in terms of the theory of energy-averaged'' Wigner-cusps yields good agreement between theory and experiment. (auth)« less