Development of the ISOLDE Decay Station and γ spectroscopic studies of exotic nuclei near the N=20 “Island of Inversion”

The main topic of my PhD Thesis is related to nuclear structure studies of neutron-rich nuclei following the beta-decay of 34Mg isotopes produced at the ISOLDE facility of CERN and measured using one of the newest permanent experimental setups, the ISOLDE Decay Station (IDS). I will also describe this setup and some of developments I contributed to during the three years spent as a PhD Student at CERN. This Thesis is divided into 6 chapters: The first chapter contains a description of the radioactive ion-beam production techniques with an emphasis on the ISOL technique and an overview of the capabilities of the ISOLDE facility of CERN. The second chapter is dedicated to the IDS setup, its capabilities and development since the first experimental campaign in 2014. The GEANT4 simulations of IDS are the subject in the third chapter, which cover mainly the HPGe detectors, the core detection system of IDS, and a possible improvement related to reducing the large background present in the high energy region of the HPGe detectors. In the fourth chapter some theoretical aspects will be discussed related to shape coexistence in nuclei with an emphasis on the N=20 “Island of Inversion” together with the physical motivation for studying the 34Al and 34Si isotopes. The fifth chapter presents the experimental setup and results from the IS530 experiment at ISOLDE, CERN, during which the beta-decay of 34Mg was studied. The interpretation of the experimental results and a comparison with state-of-the-art shell-model calculations will be discussed in the sixth chapter followed by conclusions and outlook

Analysis algorithm for digital data used in nuclear spectroscopy

Data obtained from digital acquisition systems used in nuclear spectroscopy experiments must be converted by a dedicated algorithm in or- der to extract the physical quantities of interest. I will report here the de- velopment of an algorithm capable to read digital data, discriminate between random and true signals and convert the results into a format readable by a special data analysis program package used to interpret nuclear spectra and to create coincident matrices. The algorithm can be used in any nuclear spectroscopy experimental setup provided that digital acquisition modules are involved. In particular it was used to treat data obtained from the IS441 experiment at ISOLDE where the beta decay of 80Zn was investigated as part of ultra-fast timing studies of neutron rich Zn nuclei. The results obtained for the half-lives of 80Zn and 80Ga were in very good agreement with previous measurements. This fact proved unquestionably that the conversion algorithm works. Another remarkable result was the improvement of 80Ga level scheme but this makes the object of a future publication and will not be detailed here

A Thermal Sublimation Generator of 131mXe

Stable and unstable isotopes of the heavy noble gas xenon find use in various medical applications. However, apart from 133 Xe, used for Single Photon Emission Computed Tomography, radioactive isotopes of xenon are currently complicated to obtain in small quantities. With the GAMMA-MRI project in mind, we investigated a thermal sublimation generator of the long-lived excited state (isomer) 131 m Xe. This production method utilized the decay of 131 I, obtained commercially from a hospital supplier in the form of Na 131 I powder. Heat treatments of the Na 131 I powder and cryogenic trapping of released 131 m Xe allowed us to collect up to 88% of the produced xenon. Our method provides an isomeric mixture of 131 m Xe and 131 Xe. With improvements in scalability and chemical purification, this method could be a cost-effective source of 131 m Xe for small-scale experiments