The purpose of the present work is to measure the neutron cross sections of gadolinium accurately. Gd has the highest thermal absorption cross section of any natural element. Therefore it is an important element for thermal reactor applications Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute (RPI) LINAC facility using metallic and liquid Gd samples. The liquid samples were isotopically-enriched in either Gd has been measured to be 11% smaller than that calculated from ENDF/B-VI updated through release 8. Thermal capture cross sections and capture resonance integrals for each isotope as well as elemental gadolinium are presented.In the epithermal region, natural metal samples were measured in capture and transmission. Neutron interaction data up to 300 eV have been analyzed. Substantial improvement to the understanding of gadolinium cross sections is presented, particularly above 180 eV where the ENDF resolved region for 155 Gd ends.

Neutron capture and transmission measurements were performed by the timeof-flight technique at the Rensselaer Polytechnic Institute (RPI) linac facility using metallic and liquid Gd samples. The liquid samplE!s were isotopically-enriched in either 155Gd or 157Gd. The capture measurements were made at the 25-mflight station with a multiplicity-type capture detector, and the transmis.soion measurements were performed at 15-and 25-m flight stations with 6 Li glass scintillan;on 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 e V in /57 Gd, has been l:'1easured to be (9:2:.1)% smaller than that given in ENDF/B-VI updated through releasE~ 8. The thermal (2200 m/s) capture cross section of /57 Gd.has been measured to be 1 J% 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 cros.s: section given by ENDF. In the epithermal region, 1-300 eV; the analysi~, provided here represents the most extensive to date. Twenty eight new resonances are proposed and other resonances previously identified in the literature have been rel-'isited. The assignment of resonances within regions of complicated structure inco,:porated the observations of other researchers, particularly on the six occasio,ns 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 jthe understanding of gadolinium cross sections is presented, particularly above 180 e V 'where the ENDF resolved region for 155Gd ends. In the epithermal energy range, natural metal samples were measured in capture and transmission. The data were analyzed with the Bayesian code SAMMY. Resonance parameters and resonance integrals have been calculated. The historical record was reviewed during the analysis and judgments have bl~en made regarding the number and location o/new epithermal resonances. The data clearly show that some resonances are needed to supplement those given in ENDF. The isotope and spin of the new resonances could not be determined and their neutron widths 11-'ere reported as 2agr n.

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