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Forum: Medical Applications
Re: Question Bragg curve profiles of protons in water (aimsphere)
Re: Feedback Re: Bragg curve profiles of protons in water (Michael H. Kelsey)
Re: Feedback Re: Bragg curve profiles of protons in water (aimsphere)
Date: 06 Jan, 2013
From: Michael H. Kelsey <Michael H. Kelsey>

On Sun, 06 Jan 2013 21:18:52 GMT, aimsphere wrote:
> Thank you for the quick response and useful information.
> 1) I am using G4.9.3 and have set QGSP_BERT and emstandard_op3 reference
> lists. Additionally the interface to JAM/JQMD model is applied as well.

Okay, thanks! That's appropriate for the study you're attempting. There might be better options, but the basic results will be similar enough to get by.

> 2) Yes right, if inelastic collisions occur then like you wrote, there
> will be fragmentation of the target nuclei in this case.

Exactly so. And once that happens, you don't really have the original primary to track. You _could_ try writing analysis code that identifies the leading (i.e., highest energy) secondary proton as equivalent to the primary, but that's only going to be statistically true, and doesn't take account of charge exchange (e.g., where the leading hadron is a neutron).

> I have been comparing range with the predictions from programs for
> validating my code such as SRIM which give ranges for particle energies
> upto 10 GeV/nucleon. But it seems like that such inelastic nucleus
> nucleus interactions are highly probable for high particle energies, at
> least by looking at my simulation results but then how can the range of
> let's say 1 GeV protons in water be 3.2 m as deduced from SRIM?

I don't know enough about SRIM to answer that directly. For water, 3.2 m sounds more like the shower profile depth.

> To me it seems that the range of primary protons in water should be much 
> shorter as the primary particle is mostly killed in outer layers.

Well, as I suggested above, you can do algorithmic tricks to pick one of the shower secondaries as being a "carryover" of the primary, but that's impossible to do correctly event-by-event (a consequence of all protons being indistinguishable :-).

> It probably is better to compare only dE/dx from my code with SRIM by
> tracking all particles including secondaries rather than comparing range
> for higher energies. Would you agree?

Yes, that's definitely the right approach. We do have built-in scorers in GEANT4, for simple volumes (like your cuboid) which can do that for you automatically.

      -- Michael Kelsey

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