|Message: Re: Cross sections of the reaction Al(p,x)26Al and Si(n,x)26Al calculated by Geant4 are different with experimental data.||Not Logged In (login)|
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Hello, let me add a comment to Daren's one. If you use the original Had03 FTP_BERT physics you get actually a lower 27Al(p,pn)26Al cross section: 408*361/5201=28.31 mb, but this is about the half of the exp. one (around 55 mb from the plot), i.e 50% relative error
On the other hand, as you pointed out, QGS_BIC produces 408*943/5151=74.69 mb, which means a relative error of 36%, not optimal, of course, but better than the former.
The origin of the differences lies on the different preequilirium models used in both physics lists, and coud be expected. In fact, at this incident energy the cascade model will deliver straightaway the (p+27Al) excited system to the preeequilibrium model There are two different exciton model versions in BERT and BIC, therefore here you have the origin of the discrepancies between them.
As for the discrepancies with respect to exp. data, this has been explained several times in several threads in the past, and also could be expected at these incident energies (around and below 100 MeV) . Simple statistical models are included in Geant4 to describe this reaction stage (the situation is similar for other MC codes: MCNP uses also exciton model and as far as I know, FLUKA and maybe PHITS use Bolzmann master equation transport model for preequlibrium, in any case simple models), which, apart of their simplicity for computational reasons, excludes a quantum mechanical treatment of the direct reaction channels (i.e., no compound system is considered and the memory of entrance channel is dominant). I'm afraid that if you need a better description of the 26Al yield at this energies you must either include by yoursel a better prescription in Geant4 (difficult, but I'd be extremely glad of that) or resort to codes for nuclear data evaluation, which use much more sofisticated nuclear models (usually several options). I suggest you to have a look to Empire (Mike Hermann et al) and/or TALYS (Arjan Koning et al) predictions for your work.
Finally, let me add, once again, that preequilirium statistical models (as exciton) are meant as backend stages after intranuclear cascade has taken place, in which situation they use to perform passably well. When they are used as "doorway" models (below 100 MeV), the situation usually isn't that good.
Jose Manuel On Fri, 21 Aug 2015 21:05:57 GMT, Daren Sawkey wrote: > > chose the G4HadronPhysicsQGSP_BIC_HP > > I'll mention that if you use G4HadronPhysicsFTFP_BERT_HP instead > (default in Hadr03) there is better agreement to the experiment. I don't > know why this is or if it is expected. >
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