155Eu analysis-extending the timeline of fission product measurement from separated element samples

Abstract

As a high mass ‘wing’ fission product, the cumulative fission yield (CFY) of ¹⁵⁶Eu varies both with incident neutron energy and actinide isotope undergoing fission. Fission product ¹⁵⁵Eu should yield comparable information to that of ¹⁵⁶Eu long after this shorter half-life radioisotope has decayed (half-life of 4.75 years versus 15.19 days). In this context a series of solid Eu₂O₃ mounts previously prepared for the measurement of ¹⁵⁶Eu have been reanalyzed for ¹⁵⁵Eu. Samples generated from the separation of europium from dissolved Highly Enriched Uranium (HEU) targets irradiated by thermal neutrons were used for technique development, with gamma-ray spectrometry proving to be an effective measurement technique. Utilizing this method two complimentary analyses paths were developed and then successfully applied to the measurement of sample sets where either the incident neutron and/or actinide fuels were varied. As would be expected, if the measurements were accurate and precise, ¹⁵⁵Eu fission yields varied in a predictable fashion with both neutron energy and actinide fuel. As further validation of the technique, the increased perturbation away from thermal fission yields as the cumulative fission yield mass chain increases was also observed (153<155<156). This was evidenced through comparison with prior analysis results for ¹⁵³Sm and ¹⁵⁶Eu. ¹⁵⁵Eu can thus be measured with a high degree of confidence in samples where both these shorter half-life radioisotopes have decayed.