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Forum: Physics List
Re: None Secondaries from heavy-ion projectiles with different physics lists (Mark Looper)
Re: None Re: Secondaries from heavy-ion projectiles with different physics lists (Mark Looper)
Date: 14 Jun, 2013
From: Miguel Cortes-Giraldo <Miguel Cortes-Giraldo>

Hi Mark,

The main mechanism which creates secondary protons (or fragments) in backwards direction is a hadronic inelastic interaction which, by means of pre-equilibrium and evaporation mechanisms, performs the emission of fragments from the excited compound (projectile + target) nucleus.

But consider that each physics list uses a different set of models to simulate the final state of an inelastic hadronic interaction (when it happens). Each model is applied within certain projectile energy thresholds, and these energy thresholds vary from a physics list to another.

Regarding the hadronic interaction of ions, the models you have used are:

1) *Shielding* physics list uses G4IonQMDPhysics builder class, which includes these models:
   - BinaryLightIon model, if the energy is below 110 MeV
   - QMD model, if the energy is above 100 MeV

2) *QBBC*, in contrast, uses G4IonPhysics builder class, which means:
   - BinaryLightIon model, if the energy is below 4 GeV
   - FTFP model, if the energy is above 2 GeV

By the way, if the projectile is within the energy range where 2 models overlap, the probability of using the low energy model decreases with increasing energy until it reaches the low energy model maximum threshold. So, for instance, in QBBC you are using Binary model until 2 GeV, between 2-4 GeV both models are used (the probability of each model depends on how far the energy is from each end of the interval) and above 4 GeV the FTFP (Fritiof+Precompound) is the only model used.

Therefore, it is very likely that the sharp changes you see in your plots are due to the change of the model used to simulate the final state. Clearly, the FTFP model produces more secondary protons than the Binary Light Ion model at 2GeV/u and it causes that difference in population. The same thing explains what you see with Shielding PL at about 100 MeV/u; in this case, the QMD model also creates more secondaries than the Binary model.

This is my interpretation of the different behaviours but, which model is better? I do not know the details of the high energy models, so this is a good question for someone more expert than me at such energies.

Regards, Miguel Cortes-Giraldo

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