Speaker
Description
Following the binary fission process, the two energetic fission fragments radiate their energy and angular momenta in the form of neutron and gamma-ray emission. These electrically neutral particles represent important signatures of fission in non-destructive assay of nuclear material and an analysis of the emitted radiation can be used to characterize the fissioning source. The emission of neutrons and gamma rays often represents the only probe we have of the nuclear fission process and the state of the fragments immediately following fission. Recent theoretical and experimental results have sparked renewed interest in the correlations between fission fragments. Of particular interest are the correlations between the fission fragment angular momenta. The most important observable related to the fission fragment angular momenta is the emission of gamma rays. It is thus of current interest to determine the correlations in the emission of gamma rays between fragments. While several conflicting models exist to model these correlations, experimental data is limited or inconclusive. In this work, we review the theoretical models showing how different models can give rise to differences in the gamma-ray emission correlations. We then review the experimental evidence, highlighting the experimental challenges involved and the expected systematic biases. Lastly, we present novel experimental techniques that allow us, for the first time, to directly determine the desired gamma-ray correlations. The technique generalizes the Maier-Leibniz Doppler-Shift method. In the original technique, the average yield of gamma rays is inferred from the small aberration of gamma-rays due to the speed of the emitting fragments. We have derived new sets of equations based on the same assumptions, showing that the aberration of gamma rays can be exploited to determine the second moment of the multiplicity distribution of gamma rays, i.e., the variances of the distributions and their covariance. We discuss this new technique, its applicability, and the experimental setups required to utilize it.