Hmmmmm, This is from: jpreisig@aol.com . MCNP5, huh??? Cool. First. look at your mcnp manual some more, especially in the tally definitions section(s). Maybe what you want to do is described in the manual. If this fails, call or e-mail the MCNP group at Los Alamos Lab. They are usually pretty good with helping mcnp users. Good Luck. Regards, J.R. Preisig, Ph.D. (Joe Preisig)