Re: [fluka-discuss]: conversation 02-06-2021. Improvements dpa calculation

From: <>
Date: Mon, 11 Oct 2021 09:38:05 +0200

Dear Mara

I'll try to give you some further details.

First of all, there is not yet any publication detailing the revised

Most of the changes are related to the treatment of particles falling
below the transport threshold.

Originally, until fluka2011.2c included, when a particle was falling below
threshold the fraction of the residual kinetic energy due to NIEL was
estimated with the Linhard partition function, let's call it T_niel.
Then the restricted NIEL, Tr_niel, and the energy available for DPA,
T_dpa, contributions were computed assuming they were equal to T_niel,
which was an overestimation, even though it is an approach more or less
consistent with what is done for example in Njoy.

Now, if the particle threshold energy is Ek_min, the restricted Tr_niel
and T_dpa are computed as follows:
   Tr_niel = T_niel x ---------------- |
                        dE/dx_niel | Ek_min

   T_dpa = T_dpa x ---------------- |
                        dE/dx_niel | Ek_min

where dE/dx_niel, dE/dx_restr_niel, dE/dx_dpa are the stopping power due
to NIEL, restricted NIEL, and restricted NIEL available for DPA at Ek_min

This approach is much more realistic (albeit it can still slightly
overestimate Tr_niel, T_dpa) and it is implemented since fluka2011.2x,
it seems a small change, however it accounts for the bulk of the change
with respect to fluka2011.2c.

Note please that DPA's are almost impossible to measure and comparisons
with other calculations depends a lot on the details how DPA's are
For example, according to its manual, apparently Njoy uses for neutrons
a very simple approach which is clearly overestimating DPA's.

I hope this help!

> Dear FLUKA authors,
> I am writing an article which is based on calculations performed on one of
> the last versions of the code (in particular the 2021.2.0).
> By reading the conversations on this mailing list I found that of
> 02-06-2021 on the dpa calculation. The email states that on the dpa value
> there is
> "still a factor ~2 less than what reported in the 2011 paper,
> because since that time many refinements and improvements have been
> implemented into the DPA calculations, particularly for particle below
> threshold. Those improvements, related to the correct applications of the
> xsi function (see eq. 2) in the 2011 paper) close to threshold are
> responsible for the present, more correct, value.".
> =>I was wondering if a citable source contains the above-mentioned
> improvements and refinements (I hope I did not miss it) or if a sort of
> explanation can be given to us, for better understanding.
> Thank you in advance,
> Kind regards,
> Mara

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Received on Mon Oct 11 2021 - 11:43:10 CEST

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