A large cavity gamma ray spectrometer for measurement of cosmogenic radionuclides in astromaterials by whole rock counting

For resolving the ongoing debate that the Earth's climate may respond to solar activity variations, it is necessary to reconstruct a high resolution time series of heliospheric magnetic field in the past and correlate it to climatic records. The solar magnetic activity modulates the galactic cosmic ray flux, which is responsible for producing radioactive nuclides in rocks on planetary surfaces and in meteorites. To measure the minute quantity of {$\gamma$} emitting cosmogenic radionuclides, we have set up a low background, highly specific and selective {$\gamma$}-ray spectrometer. Using this spectrometer, we have reconstructed the solar activity over the past 3 centuries by measuring 44Ti and 26Al in meteorite falls; in particular we have shown that the intensity of cosmic rays has linearly decreased, in agreement with some models proposed for the past solar activity. In order to improve the Ge-NaI coincidence spectrometer, crucial for selective 44Ti detection, we have developed a multiparametric acquisition system. The flexibility of optimizing appropriate energy channels allows more reliable measurement of the small activity present in meteorites.