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Forum: Event and Track Management
Re: None CT Simulation (Lei)
Date: 18 Jul, 2003
From: Vladimir Ivanchenko <Vladimir Ivanchenko>

On Thu, 17 Jul 2003, Lei wrote:

> *** Discussion title: Event and Track Management
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/eventtrackmanage/93"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> Hello,
> 
> I am a first-time user of Geant4. Now I have finished the installation
> and begin to build up my first simulation model: simulation of CT scan.
> This model is pretty simple. I am using water cylinder as the phantom
> and a lead detector to get the projection data. The lead detector is set
> as the sensitive detector and the world volume is a big box containing
> air, phantom and detector. At present, I have got the projection data,
> but need to separate them into primary and scatter, hence, get the
> primary-to-scatter ratio. I have hard time in finding a way to do it,
> although I know there are many. Acturally, I think I haven't quite
> understood several concepts of Geant4. Here are my questions and
> confusions.
> 
> 1. What's the difference between Track and Step? My Understanding is
> that they contain different info of the interaction of the object and
> particle but they are generated at the same time in the Geant4 process.
> Is this correct? What kind of user-defined action should be set in
> "XXXXSteppingAction" and what in "XXXXTrackingAction"? Which one will be
> called first by the G4EventManager during one event process?
>

Both classes are used for tracking: G4Track includes extended description 
of a particle, simulation is performed step by step, which is 
reflected in G4Step. The purpose of actions described in the manual and in 
the comments to the interfaces.  

 
> 2. In the user guide, it says the XXXXStackingAction will push the
> generated tracks into different stacks, so simulation will be done
> accordingly. Does it mean after every track is generated, it will will
> be classified by StackingAction? What time will the tracks be poped by
> the G4EventManager (or somewhat else)? Those tracks in fWaiting stack
> will be pushed into fUrgent when fUrgent is empty. What time will
> fUrgent be empty? After the event is finished or one step is finished?
> 

When event is finished all stacks expept "suspended" are empty.

> 3. What is the rule of Track ID number? If the Track ID is 0, does it
> mean the particle is primary definitely? According to my on hand
> simulation results, it seems not true...So, what info can I use to
> identify the primary particle in my CT simulation model?
> 

For primary particle ParentID = 0

VI

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