Neutron capture measurements and resonance parameters of dysprosium

Abstract

Neutron capture yields of dysprosium isotopes (Dy-161, Dy-162, Dy-163, and Dy-164) were measured using the time-of-flight method with a 16 segment sodium iodide multiplicity detector. The measurements were made at the 25m flight station at the Gaerttner LINAC Center at Rensselaer Polytechnic Institute. Resonance parameters were obtained using the multilevel R-matrix Bayesian code SAMMY. The neutron capture data for four enriched dysprosium isotopes and one natural dysprosium sample were sequentially fitted. New resonances not listed in ENDF/B-VII. 1 were observed. There were 29 and 17 new resonances from Dy-161 and Dy-163 isotopes, respectively. Six resonances from Dy-161 isotope, two resonances from Dy-163, and four resonances from Dy-164 were not observed. The capture resonance integrals of each isotope were calculated with the resulting resonance parameters and those of ENDF/B-VII. 1 in the energy region from 0.5 eV to 20MeV and were compared to the capture resonance integrals with the resonance parameters from ENDF/B-VII. 1. A resonance integral value of the natural dysprosium calculated with present resonance parameters was 1405 +/- 3.5 barn. The value is similar to 0.3% higher than that obtained with the ENDF/B-VII. 1 parameters. The distributions of the present and ENDF/B-VII. 1 neutron widths were compared to a Porter-Thomas distribution. Neutron strength functions for Dy-161 and Dy-163 were calculated with the present resonance parameters and both values were in between the values of "Atlas of Neutron Resonances" and ENDF/B-VII. 1. The present radiation width distributions of Dy-161 and Dy-163 were fitted with the chi(2) distribution by varying the degrees of freedom.