  A simple, self-contained, thermo-electrically cooled SiPM system is presented
which cools a SiPM array to -20 C. The array views a NaI scintillator through a
75 mm diameter glass window. Waste heat is removed with a large heat sink and
AC fans. Above 40 keV in an air-coupled 2" x 2" NaI scintillator, the SiPM dark
count rate was reduced by a factor of about 1000 when cooled. Spectroscopic
performance when cooled was very similar to a PMT tested in the same setup, and
adequate for nuclear spectrsocopy above 25 keV. Originally, water cooling was
used but it was replaced by air cooling which is more suitable for a
self-contained system, giving the advantage of portability without degrading
performance. Straightforward improvements would allow cooling the SiPM to -30 C
or below, which would further reduce the dark count rate and extend the
spectroscopically useful range to even lower energies. Such a system would be
rugged and suitable for field use, for instance for inspection of cargo for
gamma ray emissions.
