Spin and parity assignment for the ground and isomeric states in ¹⁰²Y

Abstract

Over the last 60 years, there have been a number of studies aimed at understanding the mechanisms that drive deformation. The A∼100 region has been particularly intriguing due to a rapid change from spherical to deformed nuclear shapes at N=59, the suddenness of these changes is not well understood. The results presented in this thesis provide new information about the shape and structure of the Z=39, N=63 nucleus, ¹⁰²Y. Previous studies at the TRISTAN facility at Brookhaven National Laboratory and at the JOSEF recoil separator at the Research Centre Julich have established the possible existence of a low-lying isomeric state in ¹⁰²Y, but no spin or parity assignments could be made, nor could the excitation energy be established.

In the current work, an initial experiment conducted using the double Penning trap system at the University of Jyväskylä, Finland, utilised the Ramsey cleaning technique to separate ions in the ground state from ions in the isomeric state. This experiment was able to establish an upper limit of 100 keV to the excitation energy of the isomeric state. In a second experiment at the University of Jyväskylä the gamma decay in 102Zr following the beta decay of long-lived states in ¹⁰²Y was measured simultaneously using a post-trap-spectroscopy setup. The results support the existence of two β-decaying states in ¹⁰²Y, and new γ-ray transitions have been added to level scheme for ¹⁰²Zr. A supplementary data set obtained at the Radioactive Isotope Beam Factory, RIKEN, Japan provided an alternative way to study the decay of the two long-lived states in ¹⁰²Y. The results confirm the two different decay chains identified previously at TRISTAN and JOSEF.

With the aid of BCS calculations, spin and parities for the ground and isomeric states in ¹⁰²Y have been assigned for the first time as 5⁻ and 0⁻ respectively, arising from the coupling of a 5/2[532] neutron and 5/2[422] proton. Combining the theoretical calculations with the experimental data it has been shown that the 5⁻ ground state predominantly populates negative parity states in ¹⁰²Zr via allowed transitions, while the 0⁻ isomeric state primarily populates positive parity states in ¹⁰²Zr via first-forbidden decays.

Date of Award	Jun 2018
Original language	English
Awarding Institution	University of Brighton
Supervisor	Alison Bruce (Supervisor)