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Question non-spherical sources for estimating geometric factor 

Forum: Space Applications
Date: 20 Sep, 2017
From: Elias Roussos <Elias Roussos>


I am trying to estimate the geometry factor of a particle telescope. &#913; macro file used for the input particles is:

/gps/particle e- /gps/pos/type Surface /gps/pos/shape Sphere /gps/centre 0 0 0 cm /gps/pos/radius 20 cm /gps/ang/type cos /gps/ene/mono 50. keV

If I use this, I can calculate the GF of the sensitive detector as:

GF = 4*PI^2*(Radius)^2*(N_detected/N_source)

and I get a result close to the expected value.

When I make a run with low energy particles that cannot penetrate the instrument shielding, it is enough to inject the paticles only from a surface in front of the collimator/telescope entrance, just to improve statistics. I defined a spherical cap with an opening e.g. of 60 deg like this:

/gps/hist/type biaspt

/gps/hist/point 0.0 0.0

/gps/hist/point 0.333 1.0

/gps/hist/point 1.0 0.0

The area of the spherical cap is: A=2*!PI*(1-cos(60))

How is the GF estimated then? unless I am doing something wron with the positioning biasing, I would have expected "N_detected" to be reduced by approx. A/(4*PI*R^2), but results do not seem to add up.

Thanks a lot in advance.

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1 Note: Re: non-spherical sources for estimating geometric factor   (Elias Roussos - 20 Sep, 2017)
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