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Re: Question Non Ionizing Energy Loss (NIEL) and Displacement Damage
Date: May 22, 21:27
From: Michael H. Kelsey <Michael H. Kelsey>

On Mon, 21 May 2018 16:01:08 GMT, jeonyboy wrote:
> Hello, I am trying to gather information of NIEL and displacement damage
> from Geant4 simulations. I am trying to shoot neutron particles on a
> variety of materials such as Hafnium Dioxide and silicon dioxide.

Geant4 does not include simulation of solids as crystalline structures, per se. In particular, there is no direct simulation of "displacement damage." If you were dealing with atomic beams, I would point you in the direction of SRIM/TRIM as a "better" simulation (one which more directly addresses your question). I don't know if something similar to SRIM exists for neutron beams.

One of the Geant4 examples, extended/electromagnetic/TestEm7 (which you already know about), does include physics processes and calculations, such as Lindhard partitioning, relevant to nuclear recoil and non-ionizing energy loss effects. But again, this example is aimed at heavy-ion interactions, and does not include neutrons as relevant particles for those processes.

> From what I've discovered, there is a GetNonIonizingEnergy function
> which I tried to use in TestEm7. However, for neutrons, I am getting 0
> value returned for nonionizing energy deposit. How do I remedy this?

The special processes in TestEm7 are only applied for GenericIon, not for neutrons. I suspect that even if you tried to simply add the processes to the neutron ProcessManager (and modified them so that IsApplicable() returned true for neutrons) you would not get physically correct results.

> Also, when I run example such as Hadr07, I can get a list of secondary
> particle created along with their min and max energies. Can I understand
> the secondaries as result of displacement damage? (See attached file).

Not really. Neutrons interact internally with individual nuclei, which (or some other transmuted species) will be produced as a recoiling secondary. However, Geant4 treats all materials as simple, uniform volumes of non-interacting particles, essentially an ideal gas with a suspiciously high density :-) Each atom is available for an interaction, but there is no "crystal potential", just as there is no valence or conduction band, or band gap, for electrons in a Geant4 "solid."

There are efforts, both within and outside Geant4, to develop additional physics processes, and in some cases, additional particles (non-scalar charge carriers in a crystal, for example), to model some of this very low-energy physics. But even these efforts don't include issues such as displacement damage due to neutrons.

  -- Michael Kelsey

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1 Question: Re: Non Ionizing Energy Loss (NIEL) and Displacement Damage   ( - Jun 06, 17:48)
(_ Idea: Re: Non Ionizing Energy Loss (NIEL) and Displacement Damage   (Vladimir Ivanchenko - Jul 04, 05:45)
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