Neutron Capture and Total Cross-Section Measurements and Resonance Parameters of Gadolinium

Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute linac facility using metallic and liquid Gd samples. The liquid samples were isotopically enriched in either ¹⁵⁵Gd or ¹⁵⁷Gd. The capture measurements were made at the 25-m flight station with a multiplicity-type capture detector, and the transmission measurements were performed at 15- and 25-m flight stations with ⁶Li glass scintillation detectors. The multilevel R-matrix Bayesian code SAMMY was used to extract resonance parameters.

Among the significant findings are the following. The neutron width of the largest resonance in Gd, at 0.032 eV in ¹⁵⁷Gd, has been measured to be (9 ± 1)% smaller than that given in ENDF/B-VI updated through release 8. The thermal (2200 m/s) capture cross section of ¹⁵⁷Gd has been measured to be 11% smaller than that calculated from ENDF. The other major thermal resonance, at 0.025 eV in ¹⁵⁵Gd, did not display a significant deviation from the thermal capture cross section given by ENDF.

In the epithermal region, the analysis provided here represents the most extensive to date. Twenty-eight new resonances are proposed, and other resonances previously identified in the literature have been revisited. The assignment of resonances within regions of complicated structure incorporated the observations of other researchers, particularly on the six occasions where ENDF resonances are recommended to be removed. The poor match of the ENDF parameters to the current data is significant, and substantial improvement to the understanding of gadolinium cross sections is presented, particularly above 180 eV where the ENDF resolved region for ¹⁵⁵Gd ends.