  We have examined long term changes in signal amplitude gain, energy
resolution and detection efficiency for the active components of the PIBETA
detector system. Beam defining plastic scintillation counters were operated in
a ~1 MHz stopped $\pi^+$ beam for a period of 297 days, accumulating radiation
doses of up to 2 Mrad. Detectors in the charged particle tracking system--a
pair of cylindrical multi-wire proportional chambers and a thin plastic
scintillation barrel-shaped hodoscope array--were irradiated during the same
running period with an average dose of ~40 krad. Individual CsI(undoped
crystal) calorimeter detectors received an average dose of ~120 rad, mainly
from photons, positrons and protons originating from $\pi^+$ hadronic
interactions as well as from $\pi^+$ and $\mu^+$ weak decays at rest in the
active target.
