核共振反应中的实验室电子屏蔽效应
Laboratory electron screening in nuclear resonant reactions
AI总结：
本研究针对窄共振反应中缺乏依据的电子屏蔽校正问题，通过简单模型估算屏蔽参数，发现现有校正方法存在偏差，建议暂不对孤立窄共振强度做屏蔽校正，并指出共振能量差异或可作为研究方向。
摘要：
非共振与共振反应数据均受实验室电子屏蔽效应影响。对于非共振反应，这类效应已有充分研究记录，可对测量得到的截面进行校正以得到无屏蔽截面。通常，计算非共振反应实验室电子屏蔽因子的流程与表达式也被应用于孤立窄共振，但缺乏足够的理论支撑或实验证据。本研究采用一个简单模型估算窄共振的电子屏蔽因子、屏蔽长度与屏蔽势。对测量数据的校正结果显示，无屏蔽共振强度的增幅小于0.2%，这与已发表的窄共振屏蔽校正因子结论相反——后者预测无屏蔽强度最多会降低25%。除非能得到相反的证明，否则建议不对孤立窄共振的测量强度进行实验室电子屏蔽校正。通过测量共振强度中几乎可忽略的差异来研究实验室电子屏蔽效应的前景并不乐观。相反，无屏蔽与有屏蔽情形下的共振能量差异或许是可测量的。作为示例，本文讨论了27Al(p,gamma)28Si反应中质心系能量E_cm=956-keV的共振案例。本文还证明，此前报道的在176Lu(p,n)176Hf反应中探测到800 keV附近共振的结论是错误的。
英文摘要：
Both nonresonant and resonance reaction data are subject to laboratory electron screening effects. For nonresonant reactions, such effects are well documented and the measured cross sections can be corrected to find the unscreened ones. Frequently, the procedure and expression to calculate laboratory electron screening factors for nonresonant reactions are also applied to isolated narrow resonances, without much theoretical support or experimental evidence. A simple model is applied to estimate electron screening factors, lengths, and potentials for narrow resonances. The corrections to the measured data result in an enhancement of the unscreened resonance strengths by less than 0.2%, contrary to published narrow-resonance screening correction factors, which predict a reduction of the unscreened strengths by up to 25%. Unless it can be proven otherwise, it is recommended that measured strengths of isolated narrow resonances not be corrected for laboratory electron screening. The prospects of investigating laboratory electron screening effects by measuring almost negligible differences in resonance strengths are not promising. Instead, the difference of the resonance energy for the unscreened and screened situation may be measurable. As an example, the case of the E_cm = 956-keV resonance in the 27Al(p,gamma)28Si reaction is discussed. It is also demonstrated that the claim of a previously reported detection of a resonance near 800 keV in the 176Lu(p,n)176}Hf reaction is incorrect.
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