Neutron Width Statistics in a Realistic Resonance-reaction Model

Paul Fanto, Yale University

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The statistical model of compound nucleus (CN) reactions is widely used in basic nuclear science, astrophysics and nuclear technology. A fundamental prediction of the model is that the width fluctuations for any reaction channel follow the Porter-Thomas distribution (PTD). A recent experiment1 on s-wave neutron scattering from platinum isotopes found that the neutron width distribution was significantly broader than the PTD. Several explanations have been proposed2-5, but none has resolved this issue. We have studied s-wave neutron scattering from Pt194 within a model that combines the statistical description of the CN states with a realistic description of the neutron channel6. Our main conclusion is that the PTD provides an excellent description of the neutron width fluctuations for a reasonably large range of model parameters around a baseline parameter set taken from the literature and tuned to available data. Within our parameter range there can be a near-threshold bound or virtual state of the neutron channel that alters the energy dependence of the average neutron width2. In this case, the usual experimental analysis would produce apparent PTD violation. We identify a narrow parameter range where this effect is significant as well as a measurable signature of the existence of such a near-threshold state. 1P.E. Koehler et al., PRL 105, 072502 (2010) 2H.A. Weidenmüller, PRL 105, 232501 (2010) 3G.L. Celardo et al., PRL 106, 042501 (2011) 4A. Volya et al., PRL 115, 052501 (2015) 5E. Bogomolny, PRL 118, 022501 (2017) 6P. Fanto, G.F. Bertsch, and Y. Alhassid, arXiv:1710.00792 (2017)

Abstract Author(s): P. Fanto, G.F. Bertsch, Y. Alhassid