Message: Re: 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 Re: Discrepancy between definition of materials using effective atomic number and true atomic number 

Forum: Medical Applications
Re: None Discrepancy between definition of materials using effective atomic number and true atomic number (David Oxley)
Date: 20 Oct, 2010
From: michel maire <michel maire>

On Fri, 01 Oct 2010 15:38:48 GMT, David Oxley wrote:
> 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.

 There is no theoritical foundation to choose Zeff = Zmean.

 1- dE/dx is proportional to electron density. This leads to the definition of (Z/A)eff = w1 Z1/A1 + w2 Z2/A2
 Then one can choose Zeff and Aeff according to this ratio

 2- if one choose Aeff = Amol, then one find Zeff = Zmol (=10)

 3- Ionisation cross section is proportional to atom density (not electron).        
 This gives a definition of Aeff : 1/Aeff = w1/A1 + w2/A2
 (in case of water one find Aeff = 18/3). Hence Zeff = 10/3 

 I let you play with TestEm0 and TestEm7 (in examples/extended/electromagnetic) to see the effects of these various choices.

        Michel

 Add Message Add Message
to: "Re: 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 ]