Speaker
Description
Neutron-induced reaction cross-sections on hafnium isotopes are important for research and nuclear applications. Hafnium is considered as a constituent of the control elements and structural materials of nuclear reactors due to its high absorption cross-section for thermal neutrons, good mechanical properties and extremely high resistance to corrosion. Hafnium is an alloying element of low activation materials. The majority of the neutron-induced reactions on hafnium isotopes populate metastable states. Experimental cross-sections provide a database for investigation of the sensitivity of nuclear models to level properties and decay schemes. The present study is an integral part of previous measurements on Hf, W and Ta isotopes and contributes to the database for consistent nuclear modelling in this mass region. Activation cross-section data for short-lived reaction products on hafnium isotopes are very scarce. Results of cross-section measurements will be presented for the following reactions. 178Hf(n,n’)178m1Hf, 179Hf(n,2n)178m1Hf, 179Hf(n,n’g)179m1Hf, 180Hf(n,2n)179m1Hf. The irradiations were carried out at the 7-MV Van de Graaff accelerator at EC-JRC, Geel. Neutrons in the 1-3 MeV energy range were produced via the 3H(p,n)3He reaction. Deuterium beam and a deuterium gas target were used to produce 5.6 and 6.5 MeV neutrons. For the production of quasi-monoenergetic neutrons between 15 and 20 MeV the 3H(d,n)4He reactions was employed. Both samples with natural composition and isotopic enrichment were employed to differentiate reactions leading to the same product. The half-lives of 178m1Hf and 179m1Hf are 4.0 s and 18.67 s, respectively. An automated pneumatic transport system was used for sample transport from the irradiation to the measurement position. Cycles of irradiations and measurements were repeated to enhance counting statistics. Corrections were applied for the gamma-ray self-absorption, secondary background neutrons, coincidence summing correction, interference between reactions leading to the same reaction product. The studied cross-sections were determined relative to 27Al(n,alpha)24Na reaction cross-section. Stacks with monitor foils were irradiated in separate irradiations in order determine flux density distributions. The neutron flux for the short irradiations was determined by normalization to the count rates registered by a Long Counter. Cross-section data for the 178Hf(n,n’)178m1Hf reaction were obtained for the first time. For the other reactions the new result extended the range of the experimental data to higher energy.
