Highly sensitive measurement of α-rays in NaI(Tl) scintillator by pulse shape discrimination with charge-sensitive analog-to-digital converter

In order to investigate the contamination due to the radioactive isotopes (RIs) in NaI(Tl) scintillator for dark matter search, a simple method of pulse shape discrimination (PSD) to extract α-rays energy spectrum was developed. Two linear signals of different timings were input into a single module charge-sensitive analog-to-digital converter. The α- and the γ-rays were discriminated by comparing the total charge integration of a pulse with the partial one. As a result, the α-rays energy spectrum with NaI(Tl) was successfully and clearly extracted. The present work showed that the PSD method was performed by the minimum electronic circuits. The sensitivity was high enough to measure RIs of a few μBq/kg in high pure NaI crystals for dark matter search.