2024 AIChE Annual Meeting

Lifetimes of Excited States in Ge-72 from Inelastic Neutron Scattering

Nuclear structure data are essential for a better understanding of the atomic nucleus and its properties. The nucleus of an atom is generally described as possessing a "shape" that can be spherical or deformed, which arises from the interactions of nucleons. For some nuclei, "shape coexistence" has been observed, which is a phenomenon that describes different deformations of the same nucleus with increasing excitation energy. In addition, nuclear structure data are necessary for constraining calculations of the nuclear matrix element for neutrinoless double-beta decay (0νββ). If this theoretical process is observed, the matrix element is necessary for determining the mass of the neutrino.

Currently, the study of nuclear structure data for the isotopic chain of Ge is being conducted at the University of Kentucky Accelerator Laboratory (UKAL). Ge nuclei have been shown to exhibit shape coexistence and 76Ge is a candidate for 0νββ, thus studying these nuclei are of multiple interests. For this project, data for 72Ge were collected using the UK 7 MV Van de Graaff particle accelerator to produce a 5 MeV proton beam that impinged upon a tritium gas target. The subsequent reaction produced monoenergetic neutrons at an energy of 4.0 MeV. The neutrons were inelastically scattering from an elemental target enriched to 97.85% 72Ge. The resulting gamma rays were detected at various angles utilizing a high-purity germanium detector. Lifetimes of the excited states were obtained from the angular distribution data making use of the Doppler effect. This analysis utilized the Doppler-shift attenuation method following inelastic neutron scattering. A linear function relating gamma ray energy as a function of the cosine of the detection angle was used to express the slowing down of the recoiling process through the material, and the resulting attenuation factor was compared to a theoretical curve to extract the lifetime value. New lifetime measurements were found in the femtosecond region for gamma rays of excited states in 72Ge, which have not been previously recorded in the Evaluated Nuclear Structure Data File (ENSDF) database maintained by the National Nuclear Data Center (NNDC). In addition, lifetime values that were previously measured agree well with those found in ENSDF. The lifetimes obtained were found within the range of 35 to 900 fs with their appropriate errors. The analysis of these data for the 72Ge isotope at UKAL will be used with other data to determine if the isotope exhibits shape coexistence and for a better understanding of its structure.

This material is based upon work supported by the U.S. National Science Foundation under Grant No. PHY-2209178. Travel funding was provided in part by the University of Kentucky’s Chellgren Center for Undergraduate Excellence and donor Terry Strange (CME Alumni). Additional funding was provided by the AIChE Chapter at the University of Kentucky and the Department of Materials and Chemical Engineering.