|Message: non-spherical sources for estimating geometric factor||Not Logged In (login)|
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I am trying to estimate the geometry factor of a particle telescope. Α 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/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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