Hello everyone, I am having a problem with MCNP. My question is how to get number of secondaries in a certain volume. For example I have a neutron beam bombarded Pb target, and I want to count all of proton formed in the target. I considered tally F4, but the unit is 1/cm**2. Who can explain the tally to me? More over, help me solve this problem, please. Thank you very much, Sincerely, Neo.