|Message: Re: Transmitted Intensity Data from Lead not building correct Linear Attenuation Coefficient||Not Logged In (login)|
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On Tue, 31 Jan 2017 15:43:18 GMT, Sahra wrote:
> Hi, i would appreciate any help i can get with this, thank you for > reading, > > I have built a simulation of a very thin lead cylinder inside a vacuum. > I placed the envelope with the particle gun, behind the lead cylinder, > and the idea is to 'count' the number of gamma rays transmitted through > this lead. > > I vary the thickness of the lead, each time, and build a graph of > thickness (cm) against Ix/Io(Transmitted Flux/Initial Flux). However, > when calculating the function of this curve, the measurements i > collected using geant4 do not match the NIST Tables of Linear > Attenuation Coefficients listed on the web. > > I simulate 10,000 gamma rays at 6MeV, and what i should get is a linear > Attenuation Coefficient of ~0.505. Instead what i get is -0.022 after > three simulations: > > 6MeV x Incident Intensity Transmitted Intensity > Pb. Thickness (cm) I(o) I(x) Ix/Io > 0.22 10000 9943 0.9943 > 0.3125 10000 9908 0.9908 > 0.625 10000 9849 0.9849 > > I am using a very simple detector construction, Primary Generator Action > and Action Initialization. > > My first thought was maybe the physics list i was using, which is > FTFP_BERT had a significant play on this, but i do not understand > physics lists enough to be able to make a judgement. > > Even a link to a somewhat similar question on this forum would be much > appreciated. > > Thank you so much for your help, Sahra >
You may run example TestEm13 with the attached macro. You will see that the cross sections are in agreement with nist-xcom values :
Photon Incoher. Photoel. Nuclear Tot. wo/ Energy Scatter. Absorb. Pr. Prd. Coherent
6.000E+00 1.749E-02 9.894E-04 2.523E-02 4.382E-02
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