New Technique for Enhancing Helium Production in Ferritic Materials

摘要

Analyses of iron samples irradiated up to 10 sup 27 n/m sup 2 in HFIR found more helium than was expected from fast neutron reactions at high neutron fluences. The helium excess increases systematically with neutron exposure, suggesting a transmutation-driven process. The extra helium may be produced in two different ways, either by fast neutron reactions on the transmuted isotopes of iron or by a thermal neutron reaction with the radioactive isotope sup 55 Fe. Radiometric and mass spectrometric measurements of the iron isotopes composing the irradiated samples have been used to determine limits on the cross sections for each process. Either of these processes can be used to enhance helium production in ferritic materials during irradiations in mixed-spectrum reactors by isotopically enriching the samples. Further work is needed to clarify the reaction mechanisms and helium production cross sections. Our measurements determined the thermal neutron total absorption cross section of sup 55 Fe to be 13.2 +- 2.1 barns. 16 refs., 3 figs., 3 tabs. (ERA citation 13:010497)