Simulation of Neutron Rich Isotopes at Beta Decay Station in SPES

The aim of this thesis is to explore the capabilities of the beta decay station to be installed at the LNL for the study of the decay of radioactive nuclei produced at the ISOL facility SPES. The β-decay station will perform γ and β energy measurements of exotic ions implanted on a moving tape. Studying the beta decay of exotic isotopes provides crucial insights into nuclear struc- ture, astrophysical processes, fundamental interactions, and the limits of our current understanding of the universe. It helps advance our knowledge in various scientific disciplines and contributes to both fundamental research and practical applications. In particular, these kind of measurements offer the possibility to test and probe the limits of the Standard Model of particle physics and help in understanding the processes that occur in stars, such as nucleosynthesis. Moreover, beta decay studies have practical implications that extend to fields such as nuclear medicine, where they contribute to the advancement of imaging techniques and cancer treatment methods. Unfortunately, due to delays that have accumulated in recent years in the implementation of measurement devices, largely caused by COVID and tech- nical difficulties encountered, the first beams will not be ready until the end of next year to make a real experiment. So this thesis is basically focused on the performance simulation of the experimental apparatus, which is prelim- inary mounted in the experimental room of the SPES building, waiting to be connected on the SPES RIBs beam line. We have simulated an experiment with 148Cs isotopes, that was already realized at ISOLDE (CERN) radioactive ion beam (RIB) facility in 2016, in or- der to investigate the region of n-rich Ba nuclei, which is known to exhibit strong octupole correlations. GEANT4 built-in radioactive decay option do not consider β decays with delayed neutron emission and furthermore the database may not be entirely up to date for exotic isotopes. To this purpose, we have first built four Wolfram Mathematica software, that shoul be run in advance of the simulation, with the purpose of obtaining as much informa- tion as possible for an exhaustive simulation. Given an ion of interest, the four software are capable of finding a complete list of all the decay processes, optimize the measuring and implantation time windows, the radioactive ac- tivities left on the tape and finally calculating the conversion coefficients to update the GEANT4 database. The simulation have provided satisfying re- sults and we expect it to became a useful tool that can help to better under- stand the measurements that will be performed in the future, once the beta decay station will be fully operational. This PhD project was done also in collaboration with CAEN S.p.A, in Ap- pendix A is described the CAEN A5202 board and in particular its perfor- mance in γ spectroscopy. The A5202 board in an application specific inte- grated circuit (ASIC) based front end, optimized to work in conjunction with silicon photo multipliers (SiPM). ASIC technology strength lays in the possi- bility of accommodating a large number of acquisition channel in reduced di- mensions and with low power consumption. The ASIC chip employed is the Citiroc-1A, which performs energy acquisition through a pulse height anal- ysis algorithm. The Citiroc-1A have been used to take measurements with a 6x6x15 mm3 Cerium-doped Lutetium Yttrium Orthosilicate (LYSO(Ce)), Caesium Iodine (CsI) and Bismuth Germanate (BGO) paired with a single 6x6 mm2 SiPM and 22Na, 137Cs and 60Co radioactive sources. The energy resolution of the photopeaks are comparable with what obtained with the same crystal, radioactive source and a charge integration digitizer (CAEN DT5720A) and whith results found on literature. The results obtained are discussed in further detail in ref. [1]. In the future, the beta decay station in SPES will also include scintillator arrays for neutron measurements in order to have a better understanding of the decaying isotopes, and the A5202 can be suitable set-up for this kind of measurements.