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