Low temperature light yield measurements in NaI and NaI(Tl)

The scintillation light output of a pure and a Thallium doped Sodium Iodide (NaI) crystal under irradiation with 5.486MeV \alpha -particles has been measured over a temperature range from 1.7K to 300K. Estimates of the decay time constant at three selected temperatures are given. For pure NaI an increase in light yield towards low temperatures could be confirmed and measured at higher precision. For NaI(Tl) below 60K an increase in light output has been found.