Yrast excitations of neutron-rich nuclei around doubly magic Tin-132

Pallab Kumar Bhattacharyya, Purdue University

Abstract

Investigation of the yrast structures of neutron-rich nuclei around the double closed shell nucleus $\sp{132}$Sn is important in the understanding of simple two-body nucleon-nucleon interactions in that region. However conventional fusion-evaporation methods do not populate these nuclei and $\beta$-decay studies are useful only in studying low spin states. The spectroscopy of these nuclei from thick target $\gamma$-$\gamma$ coincidence measurements of deep inelastic heavy ion collisions as well as from fission fragment $\gamma$-ray studies using large multidetector arrays are presented in this thesis. Analyses of data from the $\sp{124}$Sn + 665 MeV $\sp{136}$Xe and $\sp{130}$Te + 272 MeV $\sp{64}$Ni deep inelastic experiments identified new yrast isomers in the N = 80 nuclei $\sp{134}$Xe and $\sp{136}$Ba which de-excite by $\gamma$-ray cascades concluding with their known $4\sp+\to2\sp+$ and $2\sp+\to0\sp+$ transitions. The isomeric decay characteristics are presented and discussed in light of the systematic features in N = 80 isotones. By analyzing fission product $\gamma$-ray data measured at Eurogam II using a $\sp{248}$Cm source, yrast level structures of the two-, three- and four-proton N = 82 isotones $\sp{134}$Te, $\sp{135}$I and $\sp{136}$Xe were developed, and the proton-proton interactions from the two-body nucleus $\sp{134}$Te were used in interpreting $\sp{135}$I and $\sp{136}$Xe levels using shell model calculations. From the same data the yrast states in the N = 83 isotones $\sp{134}$Sb, $\sp{135}$Te, $\sp{136}$I and $\sp{137}$Xe were explored, and key proton-neutron interactions were extracted from the $\sp{134}$Sb level spectrum which were used in interpreting the levels of the other N = 83 isotones. Similarly yrast states in previously unexplored N = 81 isotones $\sp{132}$Sb and $\sp{133}$Te were also identified and interpreted with shell model calculations; the $\sp{132}$Sb level spectrum yielded important proton-neutron hole interactions. Neutron core-excited states at higher energies were also identified in most of these nuclei. For establishing isotopic assignments of unknown cascades, the $\gamma\gamma$ cross coincidences between heavy and light fission partners were vital. Overall, both deep inelastic and fission product studies have contributed to the exploration of an otherwise inaccessible region of the nuclidic chart. This opens up a new horizon in studying the structure of these important neutron-rich nuclei.

Degree

Ph.D.

Advisors

Daly, Purdue University.

Subject Area

Nuclear physics|Nuclear chemistry

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