Hi Khadijeh, I assume that you have a very large number of histories, and MCNP is warning you that it may be using the same random numbers (after exceeding the max).

You can fix this by using the "RAND" card and increase the "stride". RAND GEN=1 SEED=1 STRIDE=300000. I just approximately doubled the 152917 I see in the warning.

This should help.

Good luck,

dimitris

Hi, Khadijeh Kanani

as another method you can use variance reduction specially cut card.

by this, the random number that you need will decrease and a warning not show (most probably)

thanks so much Rasul Shamohamadi

thanks so much Dimitrios Kontogeorgakos Dimitrios Kontogeorgakos