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Forum: Event and Track Management
Re: Question Tracking only one type of particle (Zack Snyder)
Re: Feedback Re: Tracking only one type of particle (Gumplinger Peter)
Re: Question Re: Tracking only one type of particle (Zack Snyder)
Date: 30 May, 2013
From: Michael H. Kelsey <Michael H. Kelsey>

On Thu, 30 May 2013 21:50:44 GMT, Zack Snyder wrote:
> Also, is there any way to string neutrons together? It seems that they
> undergo an inelastic collision and for some reason Geant wants to treat
> that as a separate particle for tracking purposes.

There is a good reason for this. Inelastic nuclear collisions produce multiple secondaries through a fairly complex process: the projectile enters the nucleus, interacts with multiple constituent nucleons, and may well disappear in one of those interactions (for example, n p -> p p pi-). In the course of either those main interactions ("intranuclear cascade"), or during de-excitation of the final fragment nucleus, new neutrons may be emitted into the final state.

For the special case of a final state with exactly one outgoing neutron, it might be plausible to "identify" that as a continuation of the original projectile. But in general, when you have two, or three outgoing neutrons (or maybe a projectile pi+ and half a dozen outgoing pions), which of the outgoing particles would you choose to be "the original"? They are indistinguishable, of course, and it may well be that none of them correspond to the original projectile (as I suggested above).

So inelastic hadronic processes always "stop-and-kill" the projectile, and produce a set of new secondaries which are then tracked.

-- Michael Kelsey

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