Experimental study of the shape of beta spectra

Since the 1970s, the study of the beta shape has been limitedly investigated. A growing interest has been noticed from several users from ionizing radiation metrology, nuclear medicine, nuclear energy for the residual power of reactors, and from fundamental physics. The existing databases are incomplete and lack of accuracy to meet their requirements. This thesis work aims to develop an experimental set-up dedicated to precise beta shape studies. A beta spectrometer has been developed based on two silicon detectors and a radioactive source in the middle and has been optimized in order to reach a quasi-4π geometry. Different radioactive source preparation techniques have been studied and their influence on the shape of the β spectrum has been quantified. The device has been characterized using the conversion electron peaks of 109Cd and 207Bi decays, and the β spectra from 14C, 36Cl, 99Tc and 204Tl decays have been studied. Even though being minimized, some distortions remain in the measured spectra that are not compatible with the precision sought. An unfolding method has been developed to correct for these distortions based on PENELOPE Monte Carlo simulations. The response function of the detection system has been built from mono-energetic simulations and the measured spectra have been unfolded by applying the matrix inversion method. Finally, the resulting spectra have been compared with some high-precision measurements performed with Metallic Magnetic Calorimeters, showing excellent agreement in the common energy range. The experimental shape factors have been extracted for 14C, 99Tc and 204Tl spectra and compared with results available in the literature.