Details

Autor(en) / Beteiligte

• Quinn, Matthew A

Titel

Beta decay half-lives of neutron rich isotopes in the Germanium-Bromine region

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2010

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Understanding the origin of the heaviest elements in the universe is one of the great outstanding problems in physics. More than half of these elements are thought to have been created by a process called the rapid neutron capture, or R process. This process involves many nuclei that are very far from the line of stability. Because these nuclei have such short beta decay half-lives, they are very difficult to produce and study. The vast majority of r-process nuclei have not been observed at all. This work details the measurement of several r-process nuclei that have never been produced before. These nuclei lie in the r-process path near the Z = 40, N = 60 region. This region of the chart of the nuclides is also interesting because a rapid change in the shape of nuclei is seen. With the addition or removal of just a few nucleons, nuclei go from a spherical shape to a strongly deformed shape. For both r-process abundance calculations and nuclear deformation calculations, the beta decay half life and beta-delayed neutron emission ratio Pn values are important parameters. This experiment determined these values for the r-process nuclei in the Germanium-Bromine region. The experimental work was carried out at the National Superconducting Cyclotron Laboratory at Michigan State University. Twenty-two halflives were determined in our measurments. Three nuclei, 90Se, 88As, and 89As, were measured for the first time. In addition, we have confirmed previously measured half-lives for Y, Sr, Rb, Kr, Br, Se, and As isotopes. The new measurements were used to calculate the Pn values for 92-90Br and 96,94Rb. An r-process simulation was performed with the results from this measurement. Because of the possible change in shape of the Se nuclei in particular, the uncertainty of r-process production abundances in the A = 90 - 130 region are as large as a factor of two. This work determined the shape of the Se isotopes in this region to be deformed, which removed this large uncertainty in the r-process calculations.