# 15th Varenna Conference on Nuclear Reaction Mechanisms

Jun 11 – 15, 2018
Villa Monastero
Europe/Zurich timezone

## Neutron width statistics in a realistic resonance-reaction model

Jun 15, 2018, 3:50 PM
20m
Villa Monastero

#### Villa Monastero

Varenna (Italy)
Nuclear reactions

### Speaker

Paul Fanto (Yale University)

### Description

The statistical model of compound nucleus reactions is widely used to calculate reaction observables for basic nuclear science, astrophysics, and nuclear technology. The prediction that neutron resonance reduced widths are distributed according to the Porter-Thomas distribution (PTD) is a cornerstone of the statistical model. Consequently, the recently measured deviations from the PTD for neutron resonance widths in $s$-wave neutron scattering off Pt isotopes [1] have generated much interest, and several explanations have been proposed within the statistical model [2-4]. We discuss a recent study of the neutron width statistics for $s$-wave neutron scattering off $^{194}$Pt within a model that combines a realistic description of the neutron channel with the usual statistical description of the internal compound nucleus states [5]. Our model enables us to calculate resonance widths and reaction cross sections within a unified framework. We explored a reasonably large range of the model parameters around a baseline set taken from the literature and tuned to evaluated and experimental data. Our main conclusion is that the PTD provides an excellent description of the reduced neutron width distribution, provided that the correct secular energy dependence of the average neutron width is used in the calculation of the reduced widths. Our result indicates that the effects of the nonstatistical interaction of the internal states through the neutron channel are not significant in this reaction. Within our parameter range, there can be a near-threshold bound or virtual state of the neutron channel that leads to an energy dependence of the average neutron width that differs from the usual $\sqrt{E}$ form, as proposed in Ref. [2]. In this case, the reduced width distribution extracted using the $\sqrt{E}$ dependence is significantly broader than the PTD. We provide a narrow range of the model parameters within which such a near-threshold bound or virtual state may occur and identify measurable signatures of its existence.

[1] P. E. Koehler, F. Bečvár, M. Krtička, J. A. Harvey, and K. H. Guber, Phys. Rev. Lett. 105, 072502 (2010).

[2] H. A. Weidenmüller, Phys. Rev. Lett. 105, 232501 (2010).

[3] G. L. Celardo, N. Auerbach, F. M. Izrailev, and V. G. Zelevinsky, Phys. Rev. Lett. 106, 042501 (2011).

[4] A. Volya, H. A. Weidenmüller, and V. Zelevinsky, Phys. Rev. Lett. 115, 052501 (2015).

[5] P. Fanto, G. F. Bertsch, and Y. Alhassid, arXiv:1710.00792.

### Primary author

Paul Fanto (Yale University)

### Co-authors

George Bertsch Yoram Alhassid (Yale University)