  In this paper we present irradiation measurements performed to select a
transparent anode substrate that best meets the requirements of an optical
readout for a novel detector, the LaGEMPix. The modification of the optical
properties of the material due to proton irradiation were studied in soda-lime,
fused quartz and fused silica glasses coated with an Indium Tin Oxide layer.
The irradiations were performed using the research Beam Transfer Line (BTL) of
the IBA Cyclone 18 MeV cyclotron of the Bern University Hospital (Inselspital).
We recorded visible scintillation light generated by proton irradiation in the
soda-lime and fused quartz samples. We also investigated the darkening of these
three glasses and observed radiation-induced colour centres in the soda-lime
glass sample. The optical transmission spectra of the samples were measured
before and after irradiation. Reductions of 45%, 1% and 0.4% were observed for
soda-lime glass, fused quartz and fused silica, respectively (with an
associated error of 0.25%). We conclude that the best option for our specific
application is the fused silica substrate, which will be the transparent anode
for the next generation of the LaGEMPix detector.
