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Question GPS interpolation 

Forum: Space Applications
Date: 25 Jun, 2013
From: Wolfgang Mai <Wolfgang Mai>

Dear colleagues,

do you know how the general particle source is interpolating arbitrary spectra?

I was using GRAS 3.1 with an SPENVIS generated macro with an diff. electron spectrum (AE-8MAX, GEO), which looked like this:

/gps/particle e-
/gps/ene/type Arb
/gps/hist/type arb
/gps/hist/point 4.000000E-02 1.138400E+10
/gps/hist/point 1.000000E-01 5.653800E+09
/gps/hist/point 2.000000E-01 5.623300E+08
/gps/hist/point 3.000000E-01 1.717600E+08
/gps/hist/point 4.000000E-01 8.587400E+07
/gps/hist/point 5.000000E-01 5.386000E+07
/gps/hist/point 6.000000E-01 3.011800E+07
/gps/hist/point 7.000000E-01 2.467300E+07
/gps/hist/point 8.000000E-01 2.042700E+07
/gps/hist/point 1.000000E+00 1.383600E+07
/gps/hist/point 1.250000E+00 8.481900E+06
/gps/hist/point 1.500000E+00 4.907300E+06
/gps/hist/point 1.750000E+00 2.598900E+06
/gps/hist/point 2.000000E+00 1.649900E+06
/gps/hist/point 2.250000E+00 9.743300E+05
/gps/hist/point 2.500000E+00 4.355700E+05
/gps/hist/point 2.750000E+00 1.797200E+05
/gps/hist/point 3.000000E+00 8.610400E+04
/gps/hist/point 3.250000E+00 4.061000E+04
/gps/hist/point 3.500000E+00 2.145000E+04
/gps/hist/point 3.750000E+00 1.119400E+04
/gps/hist/point 4.000000E+00 4.665900E+03
/gps/hist/point 4.250000E+00 1.943400E+03
/gps/hist/point 4.500000E+00 8.365100E+02
/gps/hist/point 4.750000E+00 3.363000E+02
/gps/hist/point 5.000000E+00 5.920500E+01
/gps/hist/point 5.500000E+00 3.613200E+00
/gps/hist/point 6.000000E+00 0.000000E+00
#/gps/hist/point 6.500000E+00 0.000000E+00
#/gps/hist/point 7.000000E+00 0.000000E+00
/gps/hist/inter Lin
/gps/ang/type cos
/gps/ang/maxtheta 90.00 deg
/gps/pos/type Surface
/gps/shape Sphere
/gps/pos/centre 0.0000E+00 0.0000E+00 0.0000E+00 mm
/gps/pos/radius 5.100000E+00 mm

#
#Normalisation
#
/gras/analysis/setNormalisationType FLUENCE
/gras/analysis/setSourceFluence 2.0767E+17 cm-2

Now what I did was cutting the first value of the spectrum and changing the fluence value in order to get a better statistic, as these particles don't contribute remarkable to my dose measurement. The macro then looked like this:

...
/gps/hist/type arb
#/gps/hist/point 4.000000E-02 1.138400E+10
/gps/hist/point 1.000000E-01 5.653800E+09
...
/gras/analysis/setSourceFluence 4.6473E+16 cm-2

The strange thing is now, that the measured dose is only half the value of the first one, although these low energy electrons don't contribute.
After that I measured the fluence of these sources I saw, that there are much more electrons over 0.1 MeV in the first case than in the second. It seems, that gps distributes the particles in a different way as they really are distributed.

Does anyone know about this problem?

Thank you in advance
Wolfgang

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