Nuclear Science and Engineering / Volume 161 / Number 3 / March 2009 / Pages 303-320
The focus of this work is to determine the resonance parameters for stable hafnium isotopes in the 0.005- to 200-eV region, with special emphasis on the overlapping 176Hf and 178Hf resonances near 8 eV. Accurate hafnium cross sections and resonance parameters are needed in order to quantify the effects of hafnium found in zirconium, a metal commonly used in reactors. The accuracy of the cross sections and the corresponding resonance parameters used in current nuclear analysis tools are rapidly becoming the limiting factor in reducing the overall uncertainty on reactor physics calculations.
Experiments measuring neutron capture and transmission are routinely performed at the Rensselaer Polytechnic Institute LINAC using the time-of-flight technique. Lithium-6 glass scintillation detectors were used for transmission experiments at flight path lengths of 15 and 25 m, respectively. Capture experiments were performed using a 16-section NaI multiplicity detector at a flight path length of 25 m. These experiments utilized several thicknesses of metallic and isotope-enriched liquid Hf samples. The liquid Hf samples were designed to provide information on the 176Hf and 178Hf contributions to the 8-eV doublet without saturation.
Data analyses were performed using the R-matrix Bayesian code SAMMY. A combined capture and transmission data analysis yielded resonance parameters for all hafnium isotopes from 0.005 to 200 eV. Additionally, resonance integrals were calculated, along with errors for each hafnium isotope, using the NJOY and INTER codes. The isotopic resonance integrals calculated were significantly different from previous values. The 176Hf resonance integral, based on this work, is ~73% higher than the ENDF/B-VI value. This is due primarily to the changes to resonance parameters in the 8-eV resonance; the neutron width presented in this work is more than twice that of the previous value. The calculated elemental hafnium resonance integral, however, changed very little.