The effect of triplet production on pair-Compton cascades in thermal radiation

We calculate the spectrum of photons resulting from electromagnetic cascadesthrough thermal radiation, and examine the consequences of including tripletproduction in these cascades. We assume that the cascade is one-dimensional,and we find that this approximation is justified in the present work forthermal radiation with temperature less than $10^{-3} mc^2$. Results areobtained for both monoenergetic and power-law primary spectra, and for avariety of path lengths. We find that triplet production is particularlyimportant in electron--photon cascades through thermal radiation when theprimary energy exceeds $10^5 m^2c^4/kT$ for propagation over small pathlengths. The importance of triplet production decreases as the path lengthincreases, and it has no effect on saturated cascades.Comment: 8 pages of compressed and uuencoded Postscript including 4 figures; hardcopy available on request; Published in M.N.R.A.S., vol. 266, pp.910-916 (1994); (preprint number ADP-AT-94-1