Monte Carlo modelling and radiation measurement with ATAGS, the XArray, and SATURN at CARIBU

Abstract

The CAlifornium Rare Isotope Breeder Upgrade (CARIBU) at Argonne National Laboratory (ANL), USA allows access to, and measurement of, a broad range of neutron-rich nuclei with high intensities and purity. These nuclei are important test cases to expand our understanding of atomic nuclear structure, nuclear astrophysical processes and nuclear energy application.

The thesis project encompasses the measurement of short-lived radioactive nuclei from CARIBU using various techniques, including Total Absorption Gamma-ray Spectroscopy (TAGS), gamma-ray coincidence spectroscopy and beta-decay spectroscopy. The two detectors used - the ATAGS spectrometer and the XArray and SATURN decay-spectroscopy station (called XSAT as a combined system) - required complex Monte Carlo radiation transport models in order to interpret the results of recent experiments.

The TAGS technique was implemented at CARIBU by the recommissioning of a large, well-type NaI(Tl) scintillator detector. The detector performance was evaluated through testing of the well-known cases of 141Cs and 140Cs. This experimental program was extended to investigate the less-well-known beta-feeding intensities of 141Xe, 140Xe and 104mNb/104Nb.

In addition, a Monte Carlo model of XSAT was constructed, validated and applied to the specific cases of 134Sb, 134mSb, 92Rb, 104Nb and 106Nb in this work. This enabled the determination of the 134mSb/134Sb branching ratio resulting from 252Cf decay, measurement of 92Rb decay with implications for the so-called 'anti-neutrino anomaly', and the interpretation of the complex spectroscopy following the beta-decay of 104Nb->104Mo and 106Nb->106Mo. This Monte Carlo modelling was a key element in obtaining and interpreting results from each of these three experiments.