Re: Aluminum Stopping Power Validation

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I think I'm using stopping power correctly now, and the results are much better. Although there still is a smaller error that I'm curious about.

I'm calculating stopping power by inverting the CSDA. That is calculating the mean path length of electrons fired into Aluminum using a logarithmic distribution of initial energies.

Then generating the range: range(g/cm^2) = mean_path_length(cm)*density_Al(g/cm^3)

Then calculating stopping power with the reciprocal of the derivative of range with respect to energy: stopping_power(MeV*cm^2/g) = (drange(E)/dE)^-1

At most energies the discrepancy is much smaller than before, although it seems to grow above 10 MeV. Any thoughts on why this might be?

I'm using the Penelope EM Physics model, in geant4.9.3.b01

I've attached plots showing the discrepancy. The first plot shows the GEANT4 electron stopping power in Aluminum generated using the inverse CSDA compared to the ESTAR stopping power. The second plot shows the calculated GEANT4 range compared to the ESTAR CSDA range in the first panel and the second panle shows the ESTAR CSDA range divided by the GEANT4 range. The second panel gives a good indication of the amount of error. It looks to be 5% or below until ~12 MeV when it seems to grow continuously.

Thanks for all the help! pat

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2009/08/19/18.08-28523-pen_stp_apx.png
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2009/08/19/18.08-49013-range_fixed.png