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Question how can i use geant4 outcome to draw the dose-depth figure of mars soil. 

Forum: Space Applications
Date: Sep 17, 22:50
From: zhiyi han <zhiyi han>

how I draw dose-depth profile in soil:

1. fitting the GCR spectra from 2Gev-100Gev, i get y1=x*10^((0.18*(log10(x))^3)-(2.6*(log10(x))^2)+9.8*(log10(x))-11);y1(particles/m2-s-sr-MeV/nuc) ;   x(MeV/nuc)


2,cut GCR spectra into 3 sections: 1-10Gev, 10-100Gev, 100-1000Gev.  
Take samples (for every sample, beam on 1000) from each section and run the simulation and get the dose data.  
(total soil depth is 2m, score mesh is 40,so dose is recorded every 5cm in soil)


3,in first soil layer(0-5cm),plot the Dose-Energy image for three sections. Fitting them. y(Gy); x(Mev),i get

1-10Gev		y2=(-(3.5*10^-32)*x^4+(7.8*10^-28)*x^3-(5.5*10^-24)*x^2+(1.6*10^-20)*x-1.5*10^-17);

10-100Gev 		y3=(-(3.1*10^-40)*x^5+(7.2*10^-35)*x^4-(5.5*10^-30)*x^3+(1.4*10^-25)*x^2+(2.3*10^-21)*x-1*10^-17);

100-1000Gev   y4=((1.8*10^-33)*x^3-(3.4*10^-27)*x^2+(1.8*10^-21)*x+3.6*10^-17);


4,dose that is produced by one particle * number of the particle = total dose.

base on my calculation, the number of particle is y1/x , dose is y2, y3, y4 for each section

so F1=(y1/x)*y2,integrate F1 from 1-10Gev,  
F2=(y1/x)*y3,  integrate F2 from 10-100Gev,
F3=(y1/x)*y4,  integrate F3 from 100-1000Gev.  sum them up, i get F4, F4=F3+F2+F1.

score box is 20m * 20m *2 m, so F4*400*(60*60*24*365)=F5, F5 is the total dose that is produced by all GCRs in this soil layer during the whole year.


but the outcome i get is about 10e-7 smaller than the reference. what is wrong? any help? THANKS for your attention and help in advance.



*****************************************************************

details:


Geant4 simulation of  radiation in Mars atmosphere and soil

version
GEANT4.10.02.p02

application
Based on B4a, changed itís geometry and physics_list, added scorerwriter in B4a Main().     (.../geant4.10.02.p02/examples/basic/B4/B4a)

physics_list  
QGSP_BERT_HP 3.0

geometry 
world       			30*m X 30*m X 140000*m  (X Y  Z)
20 layers of air.(upon soil)   		20*m X 20*m X 70000*m  (X Y  Z)
Soil layer(under the air layers) 			20*m X 20*m X 20*m (X Y  Z)

primary generator(particle gun)
particle:proton
position(0, 0, -70000*m) (X Y  Z)
direction(0, 0, 1*m)(X Y  Z)


dose, energy deposition, secondaries data collected from run1.mac boxMesh. Scorer size is 20*m X 20*m X 2*m (X Y  Z), every layers is 5*cm along Z axies.

/score/create/boxMesh boxMesh_1
/score/mesh/boxSize 10 10 1 m
/score/mesh/nBin 1 1 40
/score/dumpQuantityToFile boxMesh_1 edep scoreenergydeposit.txt
/score/dumpQuantityToFile boxMesh_1 ndar scorenumberofsecondaries.txt
/score/dumpQuantityToFile boxMesh_1 dpo  scoredosedeposit.txt

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