Gamma-ray-induced surface defects in YBa2Cu3Ox (x ≈ 7) have been investigated by thermally stimulated luminescence (TSL) following storage of the samples in dry (vacuum), oxygen, and 98% relative humidity environments. Irradiation of samples stored in either vacuum or oxygen environments shows that no insulating chemical species are formed on the surface of the superconductor. In contrast, exposure to the humid environment produces various chemical components on the surface, and, consequently, enhances the TSL yield. Comparison of the YBa2Cu3Ox, TSL glow curve and emission spectra with those of BaCO3 suggests that one of the components contributing to the purported YBa2Cu3Ox luminescence is BaCO3. Evidence for formation of other chemical species and the suitability of the TSL technique for their determination are discussed.