  Detectors proposed for the International Linear Collider (ILC) incorporate a
tungsten sampling calorimeter (`BeamCal') intended to reconstruct showers of
electrons, positrons and photons that emerge from the interaction point of the
collider with angles between 5 and 50 milliradians. For the innermost radius of
this calorimeter, radiation doses at shower max are expected to reach 100 Mrad
per year, primarily due to minimum-ionizing electrons and positrons that arise
in the induced electromagnetic showers of e+e- `beamstrahlung' pairs produced
in the ILC beam-beam interaction. However, radiation damage to calorimeter
sensors may be dominated by hadrons induced by nuclear interactions of shower
photons, which are much more likely to contribute to the non-ionizing energy
loss that has been observed to damage sensors exposed to hadronic radiation. We
report here on the results of SLAC Experiment T-506, for which several
different types of silicon diode and gallium-arsenide sensors were exposed to
doses of radiation induced by showering electrons of energy 3.5-13.3 GeV. By
embedding the sensor under irradiation within a tungsten radiator, the exposure
incorporated hadronic species that would potentially contribute to the
degradation of a sensor mounted in a precision sampling calorimeter. Depending
on sensor technology, efficient charge collection was observed for doses as
large as 270 Mrad.
