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Forum: Analysis
Re: None Different energy loss in two method (Kavita Lalwani)
Re: None Re: Different energy loss in two method (Kavita Lalwani)
Re: None Re: Different energy loss in two method (Kavita Lalwani)
Re: None Re: Different energy loss in two method (Tsukasa Aso)
Date: 04 Jun, 2012
From: Kavita Lalwani <Kavita Lalwani>


Thanks and let me now elaborate my problem.

I am working on the simulation of Detector elements of Proton Computed Tomography for Cancer therapy.

Brief Description of Detector Geometry: Beam: proton pencil beam, KE: 200 MeV Geometry: Two fibers before water phantom and two after phantom to measure the incoming and outgoing position of proton and at the end, a calorimeter made up of 100 layers of scintillators to measure the energy of outgoing proton.

We are using Rohacell as a glue to attach the Fiber layers. Description for Fiber Tracker: 2 XY pair before and 2 XY pairs after the phantom. An XY pair is referred to as a plane. Plane size: 200 mm x 240 mm (upstream of phantom), 240 mm x 300 mm (downstream of phantom. Fiber: 0.5 mm (outer diameter). Material: Polystyrene. Within a plane, the X and Y fibers is separated by 2 mm of Rohacell or 0.15 mm of Mylar.

I am calculating entry and exit theta angles at Glue (Rohacell and Mylar separately) along z (beam direction) (below)

//****************************code start*************************************
     G4StepPoint* point1 = fStep->GetPreStepPoint();
     G4StepPoint* point2 = fStep->GetPostStepPoint();
     G4ThreeVector direction = fTrack->GetMomentumDirection();

         if(fTrack->GetVolume()->GetName() =="RohacellLayerPhys3")
               if (point1->GetStepStatus() == fGeomBoundary)
                analysis->theta_in_roha3  = std::acos(direction.z());

              if (point2->GetStepStatus() == fGeomBoundary)
           analysis->theta_out_roha3   = std::acos(direction.z());


//****************************code end************************************* Note: here analysis is a pointer for analysis class.

and plotted these angles only for those protons who have non zero deposited energy in calorimeter.

I have following queries:

1) Is above method is correct to calculate the entry and exit angles at any detector boundary.

2) I have calculated entry and exit angles for two glue material Rohacell & Mylar (density & thickness are defined below) in all four fiber trackers.

For Rohacell {C(5)H(8)O(2)}: density: 0.032g/cm^3, thickness : 0.2 mm For Mylar {C(10)H(8)O(4)}: 1.4 g/cm^3, thickness: 0.15mm

After seeing output, I found that Proton Inelastic interactions are large in water, calorimeter etc in case of Mylar layer as compare to Rohacell. Why it is so? and

3) why the RMS of angles of Roha layers 3 & 4 are large and deposited energy are less as compare to Mylar 3 & 4. (attached plots for 5k).

I would be thankful if any G4expert can give explanation for the above queries.

Thanks & Regards

Kavita Lalwani

Research Associate, Department of Physics & AstroPhysics, University of Delhi


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