Measurement of intrinsic radioactive backgrounds from Cs-137 and U/Th chains in CsI(Tl) crystals

TL;DR

This study measures the intrinsic radioactive backgrounds in CsI(Tl) crystals, crucial for dark matter detection, by analyzing contamination levels and decay chains using underground laboratory data.

Contribution

It provides detailed measurements of internal radioisotope contamination and decay chain identification in CsI(Tl) crystals for the first time.

Findings

Contamination levels of Cs-137, Th-232, and U-238 series are quantified.

Identification of alpha peaks from U/Th decay chains achieved.

Upper bounds set for U-235 series contamination.

Abstract

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.