Intrinsic Radioactivity in a GSO Crystal and Limits on Double Beta Decay of 160 Gd

Scintillating crystal detector offers potential advantages in low-energy low-background experiments for particle physics and astrophysics. The GSO crystal is an interesting detector to explore for future neutrino physics experiments. The contributions to background due to the various channels of intrinsic radio-isotopes from the 232 Th and 238 U series are identified and studied with time-correlation analysis and detailed fits to the spectral shape. Good agreement is achieved between measured and simulated spectra, indicating background suppression factors to the 10 −2 − 10 −3 level are possible. The procedures can be adopted for background understanding and suppression in other low-count-rate experiments where the dominant source of background is from internal radioactivity. Based on 1656 hours of data taking, limits on the double beta decay half-life for the various channels in 160 Gd are presented. The limit for the neutrinoless mode is T 0νββ 1 2 > 2.0(0.8) × 10 20 y at 68(90)% confidence level.