# MCNP6.2: F6:N and F6:P tallies vs +F6 tallies?

• 19matthew89
In summary, the conversation includes a question about comparing tallies in the case of MODE:N P, an aside question about the role of the SD card and its effect on tallies, and a solution to a discrepancy found when using SD for +F6 but not for F6:P and F6:N. It is stated that whatever the SD card does to +F6 should be the same for F6:N or F6:P and the manual describes +F6 as "collision" and F6 as "track length." The conversation also mentions the normalization of F6 tallies to the mass of the cell, defined as volume multiplied by density.
19matthew89
TL;DR Summary
In case of MODE:N P, is +F6=F6:N+F6:P
Hi,

I am checking whether, in case of a MODE:N P, tallies can be compared.
In theory, is +F6=F6:N+F6:P? If so, my numbers do not add up.

But maybe it's due to the role of SD card, so here there is an aside question: how does SD card affect the F6 tallies? Is it exactly like for F4 and F2? For instance, for F4, is the value of the tally without SD equal to the values of the tally with SD * (values of SD/volume)?

Whatever the SD card does to +F6 should be the same for F6:N or F6:P.

The manual describes +F6 as "collision" and F6 as "track length." There is some description of these in the theory manual. Presumably they will converge for large numbers of particles. Do your numbers match within the statistical error estimate?

Alex A
Grelbr42 said:
Whatever the SD card does to +F6 should be the same for F6:N or F6:P.

The manual describes +F6 as "collision" and F6 as "track length." There is some description of these in the theory manual. Presumably they will converge for large numbers of particles. Do your numbers match within the statistical error estimate?
Hi! Thanks.

I have actually checked and using SD= 1 for F6:N, F6:P and +F6 gives exactly the result I was expecting, namely +F6=F6:N+F6:P.

So I guess that the discrepancy I had found when I had used SD for +F6 but not for F6:P and F6:N had to do with what SD actually does.

EDIT: solved

The normalization of F6 tallies is to the
mass=volume*rho
where rho is the density used in defining the cell.

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