|Message: Re: bug? in Be(p,n) reaction gamma spectrums using QGSP_BERT_HP and QGSP_BIC_HP has big difference||Not Logged In (login)|
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Hello Michel, sorry for the very late reply . This an old and recurrent issue: I agree with Vladimir's next message on this subject: cascade models are not intended for such low energies. Anyhow, I guess that it's easy to understand what happens (which doesn't mean that we have a solution for it just now). In fact, although we call them "cascade models", the cascade model takes care of the initial stage of the nuclear reaction chain, namely from around ~3 GeV incident nucleon energy downwards until around 70-90 MeV, when preequilbrium (followed by de_excitation) takes over. Therefore in your case, given the very low energy of the incident proton, the reaction will proceed automatically through equilibrium de_excitation. In other words, cascade does not play any role in this case since equilibrium de_excitation will directly be called and therefore it will be the only mechanism into play (according to the sequence sequence in decreasing energy : cascade-> pre-equilibrium -> de_excitation). 1) Bertini uses its own pre-quilibrium + de-excitation. If evaporation happens in this latter stage (as I suspect), a continuum of gammas is produced, as the residual excited nuclei are produced with a countinuous distribution of excitation energies, according to Weisskopf-Ewing model. 2) INCL in principle used its own de-excitation models (ABLA). Now it can use the same "native" G4 de_excitation models (i.e., the same than Binary cascade) 3) Binary uses the "native" Geant4 de_excitation models. Now, by default, if the mass of the compound system is lighter than 17 (as in this case) Fermi Break Up model is called and just few partitions are allowed (according to the fragments in "Fermi Configuration list" in the model) . This is the reason why you see the clear peak at 3.5 MeV in the evaporated photons, coming evidently from the de_excitation of the 6Li fragment (the small fluctuations around it come from the Lorentz boost from CM to LAB system). Now, your question : which is right? Pretty sure, none of them, since, as Vladimir rightly states, they are not intended for such low incident energies. Full quantum mechanical and involved models (we are in a few body problem @ low energies ..) should be used, out of scope and reach in MC calculations (and moreover without guarantee of noticeable improvement) . Resorting to evaluated data would be the best option and this is the goal of G4ParticleHP, which is still under development. There are attemps of including more detailed models (as the one reported in this forum by S. Albright for deuteron breakup in Geant4; there has also been recently a deuteron breakup model included in MCNPX, etc..), but they are just for special cases of special interest. To my knowledge, no general solution nor definitive answer , I'm sorry. It's not necessarily a bug, is an intrinsic limitation of the models. Best regards J. M. Quesada On 12/11/2013 05:18 PM, michel maire wrote: > *** Discussion title: Hadronic Processes > > On Sun, 08 Dec 2013 09:47:51 GMT, ja wrote: >> the gamma ray spectrum given by QGSP_BIC_HP has a strong peak at 3.5 MeV >> due to 9 Be(p,a)6 Li, while the spectrum obtained using QGSP_BERT_HP is >> a continues one without peak. >> > I ran Hadr03 with following macro, for 3 physics constructors : bertini, qbbc (which use binary cascade) and inclxx. > Gamma plots confirm what you say. Log files give some informations of what happens. > I am not expert enough to tell you which physics is/are correct or not. > > # > # Macro file for "Hadr03.cc" > # > /control/verbose 2 > /run/verbose 2 > # > /testhadr/det/setIsotopeMat Be9 4 9 1.85 g/cm3 > # > /run/initialize > # > /gun/particle proton > /gun/energy 9 MeV > # > /process/list > /process/inactivate hadElastic > # > /analysis/setFileName jack_incl > /analysis/h1/set 3 100 0 5 MeV #gamma > # > /run/beamOn 100000 > > Attachment: > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-38652-bert.log.txt > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-20040-incl.log.txt > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-66731-qbbc.log.txt > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-96302-bert.gif > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-66894-incl.gif > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2013/12/11/08.16-98328-qbbc.gif > > ------------------------------------------------------------- > Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or unsubscribe) at: > http://hypernews.slac.stanford.edu/HyperNews/geant4/get/hadronprocess/1365/1.html > -- José Manuel Quesada Molina Departamento de Física Atómica, Molecular y Nuclear Facultad de Física Universidad de Sevilla Apartado 1065 41080 Sevilla, España Tel:+34.954559508 Fax:+34.954554445 http://personal.us.es/quesada/