Message: Discrepancy between definition of materials using effective atomic number and true atomic number Not Logged In (login)
 Next-in-Thread Next-in-Thread
 Next-in-Forum Next-in-Forum

None Discrepancy between definition of materials using effective atomic number and true atomic number 

Forum: Medical Applications
Date: 01 Oct, 2010
From: David Oxley <David Oxley>

Dear all,

I am trying to define materials in G4 using their effective atomic number. Later I also want to look at effective electron density, but that will not be the subject of this post.

This is because I want to know how significantly an error in the effective atomic number effects the range of protons. So I want to define the material in two different ways, add an uncertainty to one and observe the difference in the Bragg peak.

As a starting point, I have defined water using both means and hoped to get the same answer, but I dont. I attach the segment of my DetectorConstruction file where both water and 'effective Water'(as I am calling it) are defined. I used the correct effective atomic number for water and its molecular mass. I cant see why this should not be the same as defining water as I have in the first 5 lines of the attached code.

I also attach a figure of the two Bragg peaks where I have noticed the problem. The black peak is with a water phantom, as I would usually define it, the red uses the effective atomic number. I have compared the black with published experimental and simulated data (admittedly only by eye) and it is in the right ball park. The red is not. These Bragg peaks are calculated by dividing the phantom geometry into 1mm bins and counting the energy deposited in each mm. The deposited energy of any particle in each bin is then plotted as a function of depth.

Nothing else has changed between the two simulations other than the material definition. Cut values, phantom geometries, physics list and beam energies are identical.

I hope I have provided enough information, but please get back to me if you have questions. Any leads on what I am doing wrong are greatly appreciated.

thanks for your time and (hopefully) help!

Dave

//=======Sample Code==========================

// First : define water as normal

// Second : define water using eff. Z

//----

// Both definitions should result in true water and should not differ

// this is the first definition of water-----------------
 density = 1.00*g/cm3;
   G4Material* Water = new G4Material("Water",density,ncomponents=2);
   G4int natoms;
   Water->AddElement(elH,natoms=2);
   Water->AddElement(elO,natoms=1);

// this is used as the second. I just exchange Water for effWater when defining my sensitive detector
   G4Element *eleffWater = new G4Element("eleffWater","EW",z=7.42,a=18*g/mole); // define water using effective Z, a and density 

   G4Material *effWater = new G4Material("effWater",1.00*g/cm3,ncomponents=1);
   effWater->AddElement(eleffWater,100.0*perCent);

// (...)--------------------

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2010/10/01/08.32-8348-figure.png

Inline Depth:
 1 1
 All All
Outline Depth:
 1 1
 2 2
 All All
Add message: (add)

1 None: Re: Discrepancy between definition of materials using effective atomic number and true atomic number   (michel maire - 20 Oct, 2010)
 Add Message Add Message
to: "Discrepancy between definition of materials using effective atomic number and true atomic number"

 Subscribe Subscribe

This site runs SLAC HyperNews version 1.11-slac-98, derived from the original HyperNews


[ Geant 4 Home | Geant 4 HyperNews | Search | Request New Forum | Feedback ]