Metrological study of the shape of beta spectra and experimental validation of theoretical models

Since the 1970s, the study of the ß shape has been limitedly investigated and there is a growing interest from several users such as ionising radiation metrology, nuclear medicine, nuclear energy, and from fundamental physics. The existing databases are incomplete and lack of accuracy to meet their requirements. In this thesis, a precise ß spectrometer in a quasi-4π geometry is developed based on two silicon detectors in sandwich with a radioactive source. Different source preparation techniques and their influence on the shape ß of the spectrum are studied. The device is characterised using the conversion electron of 109Cd and 207Bi decays, and the ß spectra from 14C, 36Cl, 99Tc and 204Tl decays are studied. An unfolding method is developed to correct the minimised distortions based on PENELOPE Monte Carlo simulations. The response function of the system is built from mono-energetic simulations and the measured spectra are unfolded by applying the matrix inversion method. Finally, the resulting spectra are compared with some high precision measurements performed with Metallic Magnetic Calorimeters, showing excellent agreement in the common energy range.

Beta spectra, Silicon detectors, Ultra-thin radioactive sources, Spectral deconvolution, Experimental shape factor , Carbon-1, Technetium-99, Thallium-204.

Full document : TEL : 2020STRAE014