|Message: Re: Bragg curve profiles of protons in water||Not Logged In (login)|
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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.
2) Yes right, if inelastic collisions occur then like you wrote, there will be fragmentation of the target nuclei in this case.
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? 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. I should find out about how SRIM calculates those ranges.
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?
Thank you for your time.
On Sun, 06 Jan 2013 19:34:49 GMT, Michael H. Kelsey wrote:
> On Sun, 06 Jan 2013 17:23:01 GMT, aimsphere wrote: > > > I simulated a water cuboid (50 m X 25 m X 25 cm) of several layers > > irradiated with a pencil beam of mono energetic protons and tracked only > > the primary particle to estimate its depth dose profile. The aim was to > > calculate Range Vs Primary particle energy (100 MeV to 10 GeV). > > What physics list did you use? Was it one of the reference lists (e.g., > QGSP_BERT), or your own? If you created your own physics list, can you > tell us what processes and models you registered for the protons? > > > What I found is that for lower energies e.g. 100 MeV to around 800 MeV, > > the Bragg peak is clearly visible but for higher energies it becomes > > lesser and lesser prominent. And also with increasing energies the > > largest dose deposition occurs at outer layers and reduces continuously > > with depth. I have difficulty in understanding this difference in depth > > dose distribution characteristics. > > > > I think there is some physical phenomenon that occurs for higher > > energies. > > Inleastic proton-nucleus interactions. Basically, the proton hits the > nucleus and induces production of secondary hadrons (pions, nucleons > knocked out, even production of strange particles at sufficiently high > energies). > > In an inelastic collision, the original "primary" particle (in your > case, the proton) is killed. The secondaries coming out may include > protons, but there's no identification of such "new" protons with the > original particle. As you can imagine, if those secondaries are > themselves energetic, they will in turn have inelastic collisions with > other nuclei in the material. This process results in a > _hadronic_shower_. The primary particle's energy is subdivided among all > of those secondaries, and their ultimate electromagnetic energy-loss > interactions with the material. > > Thus, your method of deriving the Bragg peak, by accumulating the energy > lost by the primary as a function of depth, won't work once the > inelastic threshold is passed. Instead, just as you describe, you'll > usually see the primary particle apparently lose all of its energy in > the first interaction (outermost layer), then disappear. > > For high energies, what you need to do is track all the particles, and > instrument a _scorer_ which records the total energy deposited in each > layer. At low energies, you'll see the characteristic Bragg peak. At > higher energies, you'll see a broader depth profile (the shower shape), > with the energy deposit at a maximum partway through, then a long tail > to higher depths. >
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