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

The luminescent properties of CsI(Na) crystals are studied in this report. Using a TDS3054C oscilloscope with a sampling frequency of 5 GS/s, we find out that nuclear recoil signals are dominated by a very fast light pulse with a decay time of similar to 20 ns, while gamma-ray signals have a decay time of similar to 600 ns. The study of n/gamma separation shows that the rejection factor can reach an order of 10(-7) with a signal efficiency of more than 80% at an equivalent electron recoil energy of 20 keV or more, and the quality factors are similar to 10 times smaller than that for CsI(TI) crystals in the corresponding energy region. It is suggested that the wavelength of nuclear recoil and gamma-ray signals is also different. Such a property makes CsI(Na) an ideal candidate for dark matter searches. (C) 2011 Elsevier B.V. All rights reserved.