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The composition dependence of optical and electrical of amorphous unirradiated and γ-irradiated thin films of Pb x Ge 42-x Se 48 Te 10 (5 ≤ x ≤ 16) deposited by thermal evaporation was measured as a function of wavelength (0.3 μm ≤ λ ≤ 2.5 μm). The optical transition was found to be indirect. The optical energy gap (E opt ) decreases with increasing concentration of Pb at.wt.% and exhibits a minimum value for the composition with 9 at.wt.% Pb and the results have been interpreted in terms of the average bond energy. The band tail (E c ) obeys Ubarch's empirical relation. The d.c. electrical resistance was measured in a temperature range of (300–455 K). The activation energy for electrical conduction decreased with increasing Pb concentration. The electronic conduction in the temperature range has been attributed to band transport mechanism. The effect of γ-radiation on the optical constants (n, k), band tail (E c ) and E elect energies as a function of composition has been determined. The results show that, the radiation causes increase in optical and electrical energies as γ-doses increase.