Heery, Jacob 
ORCID: 0000-0002-3023-9907
(2021)
Developing a charge plunger method for lifetime measurements in heavy elements.
PhD thesis, University of Liverpool.
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Abstract
The use of the charge plunger method with a mass recoil separator provides a means of measuring the lifetime of low-lying states in exotic nuclei which de-excite via transitions with large internal conversion coefficients. These lifetime measurements provide tests for theoretical models predicting the structure of nuclei far from stability. The charge plunger method was used in an experiment at the University of Jyväskylä Accelerator Laboratory with the purpose of measuring the lifetime of excited states in ¹⁷⁸Pt which de-excite through γ-ray transitions and internal electron conversions. The DPUNS plunger device was connected to the in-flight mass separator MARA which separated ions by their charge state. Ionic charge-state distributions (CSD) were then observed at the focal plane of MARA. The JUROGAM 3 spectrometer surrounded DPUNS and was used to select ions in coincidence with γ-ray transitions in ¹⁷⁸Pt. Ionic charges were selected by MARA and measured at the focal plane in coincidence with the 4₁⁺→2₁⁺ 257 keV γ-ray transition detected using JUROGAM 3. The resulting CSD were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the 2₁⁺ state in ¹⁷⁸Pt. As an alternative analysis, ions were selected in coincidence with the ¹⁷⁸Pt alpha decay (Eₐ = 5.458(5) MeV) in the double-sided silicon strip detector (DSSSD) at the focal plane of MARA. Lifetime information was obtained by fitting a two-state Bateman equation to the decay curve with the lifetime of individual states defined by a single quadrupole moment. This yielded a lifetime value of 430(50) ps for the 2₁⁺ state, and 54(6) ps for the 4₁⁺ state. An analysis method based around the Bateman equation will become especially important when using the charge plunger method for the cases where utilising coincidences between prompt γ rays and recoils is not feasible.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Science and Engineering > School of Physical Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 28 Oct 2021 14:04 |
| Last Modified: | 18 Jan 2023 21:26 |
| DOI: | 10.17638/03141284 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3141284 |
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