The unit of energy deposition and fluence

Dear Fluka experts,

I used USRBIN to simulate the energy deposition and neutron fluence, I am confused about the units.

The unit of energy deposition is GeV/cm^3/unit primary weight and the unit of fluence is particles/cm^2/unit primary weight in the manual. Regarding the units, I don’t quite understand the " unit primary weight ". Could you please explain it to me?

Best regards,

Qi Ding

Dear Qi Ding,

The per unit primary weight is a more general normalization in Monte Carlo simulations (thus in FLUKA) than per primary particle.

It is possible to have biased sources via user routines, meaning not every primary particle have the same importance / weight.

If the source is not biased, – which is usually the case – the weight of one primary is 1.0. This means the number of primaries and the total weight of the primaries has the same numerical value, and the results eventually be per primary particle.

If the source is biased, then the results must to be normalized by the total (summed) weight of the primaries and not by the number of primaries, get a result related to a primary particle with a weight 1.0. (The same result as with an unbiased source.)

At the end, even you have a biased source, calling the result per primary particle is perfectly fine.

I hope this clarifies the topic.


Dear David,

Thanks a lot for your detailed response.
Now I understand it much more.

Best regards,

Qi Ding