  The last decade has increasingly seen the use of silicon photomultipliers
(SiPMs) instead of photomultiplier tubes (PMTs). This is due to various
advantages of the former on the latter like its smaller size, lower operating
voltage, higher detection efficiency, insensitivity to magnetic fields and
mechanical robustness to launch vibrations. All these features make SiPMs ideal
for use on space based experiments where the detectors require to be compact,
lightweight and capable of surviving launch conditions. A downside with the use
of this novel type of detector in space conditions is its susceptibility to
radiation damage. In order to understand the lifetime of SiPMs in space, both
the damage sustained due to radiation as well as the subsequent recovery, or
annealing, from this damage have to be studied. Here we present these studies
for three different types of SiPMs from the Hamamatsu S13360 series. Both their
behaviour after sustaining radiation equivalent to 2 years in low earth orbit
in a typical mission is presented, as well as the recovery of these detectors
while stored in different conditions. The storage conditions varied in
temperature as well as in operating voltage. The study found that the annealing
depends significantly on the temperature of the detectors with those stored at
high temperatures recovering significantly faster and at recovering closer to
the original performance. Additionally, no significant effect from a reasonable
bias voltage on the annealing was observed. Finally the annealing rate as a
function of temperature is presented along with various operating strategies
for the future SiPM based astrophysical detector POLAR-2 as well as for future
SiPM based space borne missions.
