Structural transformations in the system lanthanum bromide – water – electrical field

We found several manifestations of severe influence of relatively week direct electrical fields on interactions of water with lanthanum bromide. The rate of dissolution of these crystals in water at the negative electrode exceeds this value at the positive electrode by several times. Pulse-like growth of solid micro-rods at the negative electrode from the solution of lanthanum bromide subjected to direct electrical field was observed. Auto-oscillations between the contents of water bound in hydrated lanthanum bromide and free water were found. These oscillations are attributed to severe difference of the electrical polarizabilities of free and bound water.

Development of a 3” LaBr3 SiPM-Based Detection Module for High Resolution Gamma Ray Spectroscopy and Imaging

Gamma radiation detection finds many applications in different fields, including astrophysics, nuclear physics and medical diagnostics. Nowadays large Lanthanum Bromide crystals coupled to Photomultiplier Tubes (PMTs) represent the state of the art for gamma detection modules, in particular for spectroscopic measurements. Nevertheless, there is an interest in substituting photomultiplier tubes with solid state photodetectors like Silicon Photomultipliers (SiPMs), owing to the latter’s significant advantages. These include insensitivity to magnetic fields, low bias voltage, compactness, fast response and mechanical robustness. The aim of this thesis work, which was carried out within the context of the GAMMA project supported by IstitutoNazionale di FisicaNucleare (INFN), is the design, development and experimental characterization of a -ray spectrometer based on large Lanthanum Bromide scintillator crystals coupled with Silicon Photomultipliers. This detector specifications are compliant with nuclear physics experiments with energies ranging from 100 keV to 20 MeV, characterized by state-of-the-art energy resolution and imaging capability, in a compact, modular and robust structure. In order to perform the readout of large scintillator crystals, a matrix of 144 Silicon Photomultipliers was designed using NUV-HD SiPMs from Fondazione Bruno Kessler (FBK). These were chosen due to their high Photon Detection Efficiency in correspondence with the peak emission wavelength of the crystal, the high cell density and low Dark Count Rate.

Shape coexistence in 94Zr studied via Coulomb excitation

In recent years, a number of both theoretical and experimental investigations have been performed focusing on the zirconium isotopic chain. In particular, state-of-the-art Monte Carlo shell-model calculations predict shape coexistence in these isotopes. In this context, the 94Zr nucleus, which is believed to possess a nearly spherical ground state, is particularly interesting since the purported deformed structure is basedon the low-lying 02+ state, making it amenable for detailed study. In order to provide definitive conclusionson the shapes of the low-lying states, two complementary experiments to study 94Zr by means of low-energy Coulomb excitation were performed. This data will allow the quadrupole moments of the 21,2+ levels to be extracted as well as for the deformation parameters of the 01,2+ states to be determined and, thus, definitive conclusions to be drawn on the role of shape coexistence in this nucleus for the first time. The first experiment was performed at the INFN Legnaro National Laboratory with the GALILEO-SPIDER setup, which, for the first time, was coupled with 6 lanthanum bromide scintillators (LaBr3:Ce) in order to maximize the γ-ray detection effciency. The second experiment was performed at the Maier-Leibnitz Laboratory (MLL) in Munich and used a Q3D magnetic spectrograph to detect the scattered 12C ions following Coulomb excitation of 94Zr targets.