|Message: Re: Photonuclear with Bertini in g4.10.00.p01||Not Logged In (login)|
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On Fri, 25 Jul 2014 20:08:21 GMT, Michael H. Kelsey wrote:
> I ran our internal unit test of BERT with gamma on 24Mg, and I don't see > any alpha production below 17 MeV. This is the same for both PreCompound > and for BERT's internal de-excitation modules. Below that threshold I > see multiple gammas, and often a proton, but that's all.
Thank you for your reply. I can confirm that. I found a threshold at about 16.45 MeV which I can't link to anything physical related to 24Mg. BUT by forcing PreCompoundDeexcitation() in the model, as suggested by Dennis H. Wright, I get the 3-alpha reaction (from a C target of course) from threshold up to about 15 MeV. So I started to think that MAYBE it had some kind of internal "threshold" which is badly calculated for Mg and not for C for unknown reasons, but your last comments might explain it well.
> BERT doesn't have any explicit "threshold" for different nuclei or > different final states. Rather, the threshold appears as a consequence > of the cascade: the gamma enters the nucleus and interacts with one > nucleon, which then starts "travelling" in the nucleus, either exiting > or having secondary collisions. > At this low energy, you'll either get the nucleon ejected or the nucleus > put into an excited state which the de-excitation code will then process > down to a ground state. The issue here may be with the order of > operations in PreCompound: if it tries to reduce the energy by throwing > off gammas first, that could be more favorable, and leave the system > with too little energy for an alpha.
Not being an expert on this topic I may be wrong but maybe at these energies the model doesn't give the best results and one could test other models which could in principle give better physics. Anyway with this model the probability of ejecting a light fragment (I guess 4He are considered like that) could MAYBE be modified to enhance alpha emission from 24Mg.
Is this the implemented physics we're talking about?
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