Parity Measurements in 70Ge

Student: Brianna Harbin (Northern Kentucky University)
Mentor: Robert Haring-Kaye (OWU Department of Physics and Astronomy)

The strong nuclear force, one of the four fundamental forces of nature and responsible for holding 99.9% of the visible matter in the universe together in atomic nuclei, has yet to be fully understood. One way to gain knowledge about this force is to test contemporary theoretical models that predict fundamental properties of nuclei based on our current understanding of the strong force. In this study, we are providing a test case for contemporary theoretical predictions by measuring fundamental structure properties of a particular germanium isotope (70Ge). Comparing these measured properties to the predicted ones provides further evidence for the reliability of the models and could lead to modifications of them that might contribute to an improved understanding of the strong force.

Previous studies of the 70Ge nucleus have left open questions about its decay spectrum, in particular the spins and parities of the high-spin states. These uncertainties have hindered the comparison between the observed high-spin level scheme and the predicted one based on recent shell-model calculations. The goal of this work was thus to measure the parity of as many high-spin states in 70Ge as possible. High-spin states in 70Ge were produced from the 62Ni(14C, a2n) reaction performed at Florida State University with a beam energy of 50 MeV. The resulting g decays were measured in coincidence using a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. These data were sorted such that the parallel and perpendicular Compton-scattering yields in a Clover detector (relative to the beam direction) were measured under the condition that another g decay in 70Ge was also detected in coincidence. By comparing the parallel and perpendicular scattering intensities, the linear polarizations of eight transitions in 70Ge were measured, leading to the confirmation of eight parity assignments. Although the high-spin transitions were too weak to measure their polarizations, the measurements for the low-spin transitions show good agreement with the polarizations measured previously as well as with theoretical predictions based on previous angular distribution measurements.