Complex sentence: Due to their high beta activity they can be detected by a Geiger counter, and their gamma output can allow analysis of their isotope composition (and therefore their age and origin) by a gamma ray spectrometer.
Split into simpler sentences: Due to their high beta activity, they can be detected by a Geiger counter. Their gamma output can allow analysis of their isotope composition (and therefore their age and origin) by a gamma ray spectrometer.