  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.
