Summary form only given, as follows. Build-up factors for gamma rays having energies up to 10 MeV have been studied in a double-layered medium using the Monte Carlo method. All secondary photons and charged particles produced were taken into account. The contribution of bremsstrahlung radiation is handled in a precise way. The results indicate that the contribution of bremsstrahlung is pronounced especially for heavy materials and the order of arrangement of the two layers has a strong effect on the values of the build-up factors.
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