Distribution of total radiation widths for neutron resonances of Pt isotopes

¹ Los Alamos National Laboratory, Los Alamos, NM 87544, USA
² Department of Physics, University of Oslo, N-0316 Oslo, Norway
³ Charles University in Prague, 180 00 Prague 8, Czech Republic

^a e-mail: paul.koehler.1@us.af.mil
^b Current address: Air Force Technical Applications Center, Patrick Air Force Base, Florida, USA

Published online: 28 May 2015

Abstract

High quality neutron capture and transmission data were measured on isotopically enriched ^{192,194,195,196}Pt and natural Pt samples at ORELA. R-matrix analysis of this data revealed resonance parameters for 159, 413, 423, 258, and 11 neutron resonances for neutron energies below 5.0, 16.0, 7.5, 16.0, and 5.0 keV for ^{192,194,195,196,198}Pt+n, respectively. Earlier analysis of data on reduced neutron widths, Γ⁰_n, showed that the distributions of Γ⁰_n for ^192,194Pt deviate significantly from the Porter-Thomas distribution (PTD) predicted by random matrix theory. In this contribution we report on preliminary results of the analysis of distribution of total radiation widths, Γ_γ, in ^{192,194,195,196}Pt+n reactions. Comparison of experimental data with predictions made within the nuclear statistical model indicates that standard models of Photon Strength Functions (PSFs) and Nuclear Level Density predict Γ_γ distributions which are too narrow. We found that satisfactory agreement between experimental and simulated distributions can be obtained only by a strong suppression of the PSFs at low γ-ray energies and/or by violation of the usual assumption that primary transitions from neutron resonances follow the PTD. The shape of PSFs needed for reproduction of our Γ_γ data also nicely reproduces spectra from several (n,γ) experiments on the neighbor nuclide ¹⁹⁸Au.