  The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum
efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and
is of significant interest for future dark matter and neutrino experiments
where high signal yields are needed.
  We report on the methods developed for in-situ characterization and
monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of
typical measured single-photoelectron charge distributions, correlated noise
(afterpulsing), dark noise, double, and late pulsing characteristics. The
characterization is performed during the detector commissioning phase using
laser light injected through a light diffusing sphere and during normal
detector operation using LED light injected through optical fibres.
