Lifetime measurements in ¹⁰²Mo interpreted in the X(5) symmetry

• Main Author: Jones, Calum Eoin
• Format: Dissertation
• Language: English
• Published: University of Brighton 2022

The A∼100 region of nuclei is an interesting case to study, because it is an area of large collective behaviour and rapid structural change. In particular the molybdenum isotopes (Z = 42) are centred between the zirconium isotopes (Z = 40), which show a rapid change from spherical to deformed structures, and the ruthenium isotopes (Z = 44) which exhibit triaxiality as they become more neutron-rich. Such behaviours provide a rich testing ground for many mathematical models, for example the Interacting Boson Model (IBM) and the Liquid Drop Model. In the current work the low-lying non-yrast structure of ¹⁰²Mo is studied and discussed in relation to the X(5) and U(5) symmetries of the IBM. An experiment was carried out at the IFIN-HH, Bucharest, Romania. A beam of ¹⁸O was delivered by the Tandem Accelerator to a target of ¹⁰⁰Mo to produce excited ¹⁰²Mo nuclei for Recoil Distance Doppler Shift (RDDS) measurements. Gamma-rays were detected with an array of 25 HPGe detectors (ROSPHERE) used in conjunction with an array of 6 silicon detectors (SORCERER) for particle selectivity at backward angles. The level scheme of ¹⁰²Mo has been measured up to 2.1 MeV including 14 excited state energies and 24 transitions. A second excited 0⁺ state at 1328.2 keV and a 3⁻ state at 1875.7 keV have been measured with gamma-ray spectroscopy for the first time. Lifetimes for both of these states and nine others have been deduced, and branching ratios and transition probabilities have been calculated where possible. Existing data for excited state energies were used with an IBM code to solve for energetically optimised level schemes, based on a number of IBM Hamiltonians representing both the limits of the model and mixed configurations. Transition probabilities were calculated from the resultant level schemes in order to provide predictions to compare with experimental results. Such comparisons reveal a mix of configurations within ¹⁰²Mo; while the transition probabilities of the triplet states around ∼750 keV resemble X(5) systematics, a more vibrational-like U(5) structure better describes the quintuplet of states around 1.3 MeV.