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Forum: Particles
Re: Question How do I define 37Ar^- (Spencer Behling)
Re: None Re: How do I define 37Ar^- (Spencer Behling)
Date: 19 Aug, 2011
From: Gumplinger Peter <Gumplinger Peter>

Hi Spencer,

> methods for setting PreAssignedDecayProperTime and PreAssignedDecayProducts.

> These are all the things that I would need to use to correctly define Ar^{1-}

> but unfortunately there are no examples included with geant that show how to

> use these classes.

You are absolutely correct, we have this functionality in Geant4 but we don't have a single example that would show the user how to use this. We hope to correct this in the near future with a redesign of extended examples.

Pre-assigned decay products are implicitly used in G4HEPEvtInterface (in novice N04).

> Has anyone used any of these methods before?

The user may assign a pre-assigned decay time for a specific track in its rest frame (i.e. decay time is defined in the proper time) by using the G4PrimaryParticle::SetProperTime() method. G4VPrimaryGenerator sets the PreAssignedDecayProperTime member of G4DynamicParticle. G4Decay uses this decay time instead of the life time of the particle type. 'Pre-assigned decay time' and 'Pre-assigned decay channel' are independent. It is possible to set 'Pre-assigned decay time' for each primary particle without setting "Pre-assigned decay channel" and vice versa.

As for the 'Pre-assigned decay channel' you have to set all kinematic properties of daughter particles and you have to give daughters momentum in the lab system (i.e sum of energy and momentum of daughters should be equal to ones of the parent particle). If the parent particle travels in the detector and its momentum at the final decay point is changed from the given momentum, daughters will be boosted automatically.

The only way the pre-assigned decay time can be set is if GeneratePrimaries is coded from scratch without any gun or source (e.g. with G4PrimaryParticle::SetProperTime(time)). Because, when using G4ParticleGun, G4SingleParticleSource or G4GeneralParticleSource there is no method that's returning a pointer to the G4PrimaryParticle which has been instantiated.

Mind you, I have never actually coded this or debugged it. I cannot comment on the graphics color scheme but the way you defined the ion looks correct to me.

Peter

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