  The performance of a silicon photomultiplier has been assessed at low
temperature in order to evaluate its suitability as a scintillation readout
device in liquid argon particle physics detectors. The gain, measured as 2.1E6
for a constant over-voltage of 4V was measured between 25degC and -196degC and
found to be invariant with temperature, the corresponding single photoelectron
dark count rate reducing from 1MHz to 40Hz respectively. Following multiple
thermal cycles no deterioration in the device performance was observed. The
photon detection efficiency (PDE) was assessed as a function of photon
wavelength and temperature. For an over-voltage of 4V, the PDE, found again to
be invariant with temperature, was measured as 25% for 460nm photons and 11%
for 680nm photons. Device saturation due to high photon flux rate, observed
both at room temperature and -196degC, was again found to be independent of
temperature. Although the output signal remained proportional to the input
signal so long as the saturation limit was not exceeded, the photoelectron
pulse resolution and decay time increased slightly at -196degC.
