Wavy Bragg curve 25 MeV protons in LiF

Hi, I’m new to FLUKA and am starting with a few elementary simulations to learn the basic concepts and settings. For 25 MeV protons (500 keV energy spread) launched to a cubic LiF target I get a Bragg curve which has some wavy details in the first 2 mm (the Bragg peak is at about 2.9 mm). I didn’t expect that. Is it an artifact due to any wrong settings in my simulation and/or USRBIN setup? Thank you in advance for your help.

Kind regards,

test protoni 25 MeV 500 keV nel LiF_22_plot

test protoni 25 MeV 500 keV nel LiF.flair (3.0 KB)
test protoni 25 MeV 500 keV nel LiF.inp (1.6 KB)

Hi Enrico,

yes, see a previous discussion. Specifically, considering the scoring resolution you ask for, you need a FLUKAFIX card limiting the fraction of kinetic energy lost in a step down to 0.02 or less (instead of the default PRECISIO value of 0.05). With

FLUKAFIX        0.02                           LiF

I get:

(which may suggest to even lower to 0.01).


Thank you very much, Francesco. I applied it and now the Bragg curve is no more wavy. I’m trying now to launch 35 MeV protons towards a LiF thin film (1 um thick) over a Si substrate, from the transversal side (the protons “see” the 1 um side of the film), and see the energy deposition vs. depth in the film. Trying with 0.01 value of that parameter for now. Besides the manual, is there a tutorial or slides I can see about the FLUKAFIX card?

Note that FLUKAFIX is needed to reduce the step size in a bulky material, according to the fine scoring resolution you aim at. In case of a thin geometry region, the step size is already limited by the region boundary, with no need for FLUKAFIX.
On the other hand, a sub-micron scoring resolution inside a 1 um layer does not make really sense, since one reaches there the limits of applicability of a condensed history code such as FLUKA.

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Thanks Francesco, understood. Sorry for bothering you again. After your previous reply I tried a simulation where - please see the figure - 35 MeV protons arrive from left to right along z onto a 500 um thick Si slab (only its top few microns framed by the USRBIN) over which a 1.7 um thick LiF film lies. The interface between the LiF film and the Si slab belongs to the Oxz plane. I used FLUKAFIX with 0.01 precision. Even though the USRBIN frames a small volume (4 mm x 6 um x 7 mm), the simulation takes into account all the sample thickness along y. The fact that the Bragg peak in the film is found at the same depth of that in the Si agrees with experimental results. The simulation result looks nice - can it also be considered realistic enough? Thank you again for your patience.

Dear Enrico, I cannot see any bothering aspect in your messages, which are very welcome.

I’d say so.

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Thank you again, Francesco. You’ve been very kind. And thanks also to all the FLUKA developers and team for this amazing piece of software.

You can try with “HADROTHErapy” default card instead of “PRECISIOn” for proton PDD simulations. In the “HADROTHErapy” default, all parameters are optimized for proton PDD calculations and you need not to worry about FLUKAFIX card.

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Thank you, good to know! I will try that option as well.

For DEFAULTS/HADROTHErapy, the fraction of kinetic energy to be lost in a step is 0.02, as with my FLUKAFIX card above, contrary to what is erroneously written in the manual (FLUKAFIX card), where ICARUS and HADROTHE are swapped by mistake (we are going to fix it).

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Ah OK. Also this is good to know! Thanks.