Measurement of intrinsic radioactive backgrounds from Cs-137 and U/Th
  chains in CsI(Tl) crystals
  The inorganic CsI(Tl) crystal scintillator is a candidate served as an
anti-compton detector for China Dark matter EXperiment (CDEX). Studying the
intrinsic radiopurity of CsI(Tl) crystal is an issue of major importance. The
timing, energy and spatial correlations, as well as the capability of pulse
shape discrimination provide powerful methods for the measurement of intrinsic
radiopurities. The experimental design, detector performance and
event-selection algorithms are described. A total of 359*3 kg-days data from
three prototypes of CsI(Tl) crystals were taken at China Jinping underground
laboratory where offers a good shielding environment. The contamination levels
of internal isotopes from Cs-137, Th-232 and U-238 series, as well as the upper
bounds of U-235 series are reported. Identification of the whole alpha8 peaks
from U/Th decay chains and derivation of those corresponding quenching factors
are achieved.
