PhD Thesis Presentation: Nuclear Structure of 122-Xe Studied via High-Statistics β+/EC Decay of 122-Cs

PhD Candidate

Badamsambuu Jigmeddorj

Abstract

The Xe isotopes are located at a possible phase change in the collective structure from vibrational to rotational. The Xe isotopes therefore were considered as potential candidates for gamma-soft nuclei or O(6) symmetry limit within the IBM. However, testing of the O(6) symmetry in Xe reveals that indeed their structure is more complicated.

The study of ¹²²Xe is a part of a systematic examination of the development of collectivity in the Xe isotopes, which are located in the Z > 50, N < 82 region that display an extraordinarily smooth evolution of simple collective signatures. In order to probe the development of collectivity in greater detail, additional information on excited states is required. Specifically, the knowledge of excited states that decay to other excited states resulting low-energy transitions which can give strong indicators of the underlying structure need to be improved.

The experiment to study ¹²²Xe with the beta-decay of ¹²²Cs was performed at the TRIUMF-ISAC facility located in Vancouver, BC, Canada. Radioactive ¹²²Cs beams from the ISAC facility were delivered to the 8pi spectrometer which was composed of 20 HPGe detectors. The isomeric and ground states of ¹²²Cs decay to the ¹²²Xe with half lives of 21 seconds and a 3.7minutes, respectively. Two sets of high-statistics data for short- and long-half-life decays were collected to have an access for potential excited states of the ¹²²Xe.

The level scheme of ¹²²Xe has been dramatically extended by 177 new levels and 482 new transitions. Using gamma-gamma angular correlation analysis, 71 spin assignments have been made for 55 levels since a spin of some levels could be assigned via several different cascades. Mixing ratios for 44 gamma-ray transitions were extracted from the angular correlation analysis. Branching ratios have been determined for all observed transitions independently in the two different data sets collected with the short- and long-cycled runs. The energy levels and relative electric quadrupole transition rates have been compared with a sd-IBM-1 calculation.

Examination Committee:

• Dr. Robert Wickham, Chair
• Dr. Paul Garrett, Advisor
• Dr. Carl Svensson 
• Dr. Dennis Muecher
• Dr. Volker Werner, External Examiner (Technische Universität Darmstadt)