Neutron Capture Measurements and Resonance Parameters of Gadolinium

Abstract

Neutron capture measurements were performed with the time-of-flight method at the Gaerttner LINAC Center at Rensselaer Polytechnic Institute (RPI) using isotopically enriched gadolinium (Gd) samples (155Gd, 156Gd, 157Gd, 158Gd, and 160Gd). The neutron capture measurements were made at the 25-m flight station with a 16-segment sodium iodide multiplicity detector. After the data were collected and reduced to capture yields, resonance parameters were obtained by a combined fitting of the neutron capture data for five enriched Gd isotopes and one natural Gd sample using the multilevel R-matrix Bayesian code SAMMY. A table of resonance parameters and their uncertainties is presented. We observed 2, 169, 96, and 1 new resonances in 154Gd, 155Gd, 157Gd, and 158Gd isotopes, respectively. Resonances in the ENDF/B-VII.0 evaluation that were not observed in the current experiment and could not be traced to a literature reference were removed. This includes 11 resonances from the 156Gd isotope, 1 resonance from 157Gd, 1 resonance from 158Gd, and 6 resonances from the 160Gd isotope.The resulting resonance parameters were used to calculate the capture resonance integrals in the energy region from 0.5 eV to 20 MeV and were compared to calculations obtained when using the resonance parameters from ENDF/B-VII.0 and previous RPI results. The present parameters gave a resonance integral value of 395 ± 2 b, which is ∼0.8% higher and ∼1.7% lower than that obtained with the ENDF/B-VII.0 parameters and with the previous RPI parameters, respectively.