Neutron capture measurements and resonance parameters of dysprosium

Abstract.

Neutron capture yields of dysprosium isotopes ( ¹⁶¹Dy, ¹⁶²Dy, ¹⁶³Dy, and ¹⁶⁴Dy 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 ¹⁶¹Dy and ¹⁶³Dy isotopes, respectively. Six resonances from ¹⁶¹Dy isotope, two resonances from ¹⁶³Dy, and four resonances from ¹⁶⁴Dy 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 0.5eV 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 $1405 \pm 3.5$ barn. The value is $\sim 0.3\%$ 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 ¹⁶¹Dy and ¹⁶³Dy 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 ¹⁶¹Dy and ¹⁶³Dy were fitted with the $\chi^{2}$ distribution by varying the degrees of freedom.