UC Berkeley

Fission yields are an important set of nuclear data observables. They are used in a number of important applications including reactor design, nuclear forensics and safeguards, nuclear medicine, and stockpile stewardship. While great advancements have been made in the understanding of fission since its discovery just over 80 years ago, there are still significant gaps and uncertainties in this knowledge. Fission yields are a prime example of an area of understanding with such gaps and uncertainties. There is significant disagreement in measured, evaluated, and theoretically predicted fission yields; a lack of standardization and regularity in fission yield evaluation; and measured fission yields often exhibit large uncertainties. To enable new developments in research and applications, improvements in the nuclear data of fission yields are required. The work presented in this dissertation seeks to improve the current understanding of the nuclear data related to fission yields.

Introductory material on nuclear data is offered, with a particular focus on the current state of fission yield nuclear data. Then, a description of the fission process is provided to establish a background on fission yield phenomenology. Finally, three chapters about three projects on fission yields and their uncertainties/covariances are presented. These chapters form the basis of this dissertation. First, an extensive review of fission yield measurements and their associated sources of uncertainty is presented. Using this review, a series of templates for expected uncertainties in fission yield measurements is established, forming a guide for experimentalists and evaluators. Second, a stochastic method for the estimation of fission yield covariances is developed. The results of this method provide a basis towards closing a crucial gap in fission yield nuclear data: a complete set of fission yield covariance information was previously absent. Finally, a new measurement of short-lived fission product yields using cyclical neutron activation analysis is discussed. The analysis of the resulting experimental data offers a novel method for fission yield determination. Together, these results advance the current understanding of fission yield nuclear data.