Ware, Timothy Christopher
(2010).
Measurement and analysis of the resolved resonance cross sections of the natural hafnium isotopes.
University of Birmingham.
Ph.D.
Abstract
Hafnium is a ductile metallic element with a large neutron absorption cross section. It can be used in reactor control rods to regulate the fission process. The NEA High Priority Request List for nuclear data presents a need for improved characterisation of the hafnium cross section in the resolved resonance region. This thesis presents new resonance cross section parameters for the six natural hafnium isotopes. Cross section measurements, supported by the NUDAME and EUFRAT projects, were performed at the IRMM Geel GELINA time-of-flight facility. Capture experiments were conducted on the 12 m, 28 m and 58 m flight paths using C\(_6\)D\(_6\) detectors and transmission experiments were performed at flight paths of 26 m and 49 m using a \(^6\)Li glass detector. The samples used were metallic natural hafnium discs of various thicknesses and hafnium oxide powders, with differing isotopic enrichments. Data analysis was performed using the least square fitting REFIT code, which was updated during this work. The use of isotopically-enriched samples enabled previously unrecorded resonances to be allocated to the correct isotope. The resulting evaluated data files extend the upper energy limits of the resolved resonance regions for the \(^{174}\)Hf, \(^{176}\)Hf, \(^{177}\)Hf, \(^{178}\)Hf, \(^{179}\)Hf and \(^{180}\)Hf isotopes, relative to the current European recommended evaluation (JEFF3.1), to 250 eV, 3 keV, 1 keV, 3 keV, 1 keV and 3 keV respectively. The natural hafnium resonance integral calculated from the new resonance parameters is 1.2% lower than the integral corresponding to the JEFF3.1 evaluated hafnium data. Comparison of calculated to experimental k-effective values for appropriate zero-power reactor assemblies show improvement over the JEFF3.1 data.
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