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 (sup 155)Gd or (sup 157)Gd. 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 (sup 6)Li glass scintillation detectors. The multilevel R-matrix Bayesian code SAMMY was used to extract resonance parameters. For many years, the accuracy of measured cross sections exceeded that required by the computer codes used for nuclear reactor calculations. With the increased use of Monte Carlo methods utilizing increased computer memory for more detailed models and greater speed to permit more histories, this situation changed. The accuracy of the cross-section data is now the limiting factor in many of these calculations. The purpose of the present work is to measure the neutron cross sections of gadolinium accurately. Gd has the highest thermal cross section of any natural element. Two large resonances exist slightly above thermal energy. The resonances are in (sup 155)Gd and (sup 157) Gd. The resonances are not resolved despite the use of separated isotopes. Isotopically-enriched (sup 155)Gd and (sup 157)Gd samples were prepared as liquid solutions with heavy water to produce uniform, thin samples. These thin samples were used in conjunction with elemental, natural metal samples.
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