Variazioni decennali e secolari del flusso di raggi cosmici rivelate dall'attività di radioisotopi cosmogenici in meteoriti

In order to study decadal- and century-scale modulation of the solar activity, two HPGe-NaI(Tl) gamma spectrometers were set up at the underground laboratory of Monte dei Cappuccini (OATo-INAF) in Torino for highly sensitive and selective measurements of cosmogenic radionuclides in meteorites. The Ti-44 activity recorded in ordinary chondrites was proposed by our research group as a proxy of the solar activity modulation at century-scale. We have already measured 22 meteorites fallen between 1766 and 2001, whose Ti-44 activity values shows the long-term evolution trend of the heliospheric magnetic field and show a significant centennial oscillation. In first place, the research activity of my thesis was dedicated to develop new procedures for the spectrometers data analysis and Monte Carlo simulations (Geant4) to reproduce the response of the spectrometers. I determined the detection efficiency of the HPGe detectors from Geant4 simulations, also by taking into account the effects of self-extinction of the sample and coincidence summation of correlated events. Therefore, I validated these simulations using measurements of Dhajala meteorite (fall 1976). The measurements of Ti-44, Na-22 and Al-26 activity in meteorite Agen (fall 1814) and Ejby (fall 2016) reveal the mid-18th century minimum of galactic cosmic ray flux, related to the Gleissberg solar cycle, and the decadal oscillation of the Schwabe cycle.