The DIRC photon detector contains ~11,000 photomultipliers (PMTs),
which are submerged in ultra-pure water. This note reports on
glass corrosion R&D conducted with PMTs in pure water. We
conclude that only limited number (~50) of the PMTs in water
are affected by rapid corrosion, while a majority of the 11,000
PMTs should last, according to our measurements, for another
ten years. The observation of PMT glass corrosion is based on
visual observations, X-ray surface analysis, ESCA surface
analysis, weight analysis, transmission measurement, as well as
detailed water trace element analysis. We also correlate these
observations with DIRC measurements of water pH factor,
resistivity, temperature, transmission, and BaBar analysis of
Bhabha and di-muon events. We also compare DIRC water purity
with that of the Super Kamiokande and K2K experiments, which
also use ultra-pure water. We provide empirical proof that
corrosion, in our particular Borosilicate type of PMT glass
window, occurs at high rate when the glass has no Zn content.
Abstract: