  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 sensors were exposed to doses of radiation
induced by showering electrons of energy 3.5-10.6 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 220
MRad.
