Neutron-gamma discrimination of CsI(Na) crystals for dark matter searches

TL;DR

This study demonstrates that CsI(Na) crystals can effectively discriminate between neutron and gamma signals based on decay times and wavelengths, making them suitable for dark matter detection.

Contribution

It provides a detailed analysis of neutron-gamma discrimination in CsI(Na) crystals, highlighting their potential for dark matter search applications.

Findings

Neutron signals have a decay time of ~20 ns.

Gamma-ray signals have a decay time of ~600 ns.

Rejection factor reaches 10^-7 with >80% efficiency at 20 keV.

Abstract

The luminescent properties of CsI(Na) crystals are studied in this report. By using a TDS3054C oscilloscope with a sampling frequency of 5 GS/s, we find out that nuclear recoil signals are dominated by very fast light pulse with a decay time of ~20 ns, while {\gamma}-ray signals have a decay time of ~600 ns. The wavelength of nuclear recoil and {\gamma}-ray signals are also different. The study of n/{\gamma} separation shows that the rejection factor can reach an order of 10-7 with signal efficiency more than 80% at an equivalent electron recoil energy of 20 keV or more. Such a property makes CsI(Na) an ideal candidate for dark matter searches.