  Measurements of the degradation in performance of 30 cm long CsI(Tl)
scintillation crystals exposed to 1 MeV photon doses of 2, 10, 35, 100 and 1000
Gy are presented. The light yield, light yield longitudinal non-uniformity,
scintillation decay times, energy resolution and timing resolution of a set of
spare crystals from the BABAR and Belle experiments are studied as a function
of these doses. In addition, a model that describes the plateau observed in the
light output loss as a function of dose in terms of increase in concentrations
of absorption centres with irradiation is presented.
