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Question Fermi Break Up: how does it really work? 

Keywords: cross section, fermi breakup, isotope production
Forum: Hadronic Processes
Date: 22 Aug, 2006
From: Sara Vecchio <sara.vecchio@pi.infn.it>

I am working on a project of hadrontherapy, whose aim is to use the beta+ isotopes production in tissues after irradiation to extract information of the dose profile. The proton beam we are going to use is the one of CATANA group, hence the example Hadrontherapy in geant4 was almost perfect to perform simulations. Anyway we found some lack on the simulation of production of isotopes, since the example is developed only for dosimetry simulation. In particular we are interested in a correct simulation of three processes: C12+p->C11+pn, O16+p->O15+pn, C12+p->C10+ppn. In order to choose the proper model, I modified the proton target in the simulation, and I extrapolated the cross sections profile from the number of C11 and O15 produced in a 2 mm target made respectively of polystirene and water. Results are compared with cross section data found in TERA 95/ 19 TRA 15. After several attempts, we found that above 40 MeV the best agreement is reached by using binary cascade. Even such solution is anyway insatisfactory at low energies, where the binary model cannot be applied and the precompound alone understimate the cross section. I finally found that the introduction of Fermi Break up could partially solve the problem, but I am still far from a solution. In fact, as you can see in the plots at www.pi.infn.it/~vecchio/work/CS/ , the introduction of fermi break-up has an evident effect only when the maximum Z for the break-up is set to a value higher than the Z of the target (i.e >6 in polystirene, >8 in water, with A>12 and A>16 respectively). Moreover, the cross sections have a too low increas for Zmax= Z_target+1, and show a peak (much higher than experimental data) when Z_max>Z_target+2 (i.e. 8 in polystirene, 10 in water). I know that I am not using the model in a proper way, since the maximum A allowed should be 17 and I used even Z=10,A=20. But I would like to know how much wrong is a simulation done with such number, so I ask your help to understand the implementation of Fermi Breakup in GEANT4 and its potentiality, and to explain the strange results we had.

P.S. the legend in the plots can be explained as follow:

Fer40 : precompound + fermi break up (0 MeV,40 MeV) , binary cascade (39 MeV, 10 GeV) t6 : Zmax= 6, Amax=12 in the fermi break up t8 : Zmax= 8, Amax=16 in the fermi break up t8-20 : Zmax= 8, Amax=20 in the fermi break up t9 : Zmax= 9, Amax=18 in the fermi break up t10 : Zmax=10, Amax=20 in the fermi break up

The curves are drawn in the order they appear in the legend, hence colours which are not present in the plot are just behind the following ones.

All the rest of the physics list is equal to the hadrontherapy example default.

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1 None: Re: Fermi Break Up: how does it really work?   (Igor A. Pshenichnov - 27 Oct, 2006)
(_ More: Re: Fermi Break Up: how does it really work?   (Sara Vecchio - 29 Oct, 2006)
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