[Ifeffit] programming error in Hephaestus??

Bruce Ravel bravel at anl.gov
Fri Jun 1 11:05:22 CDT 2007


On Friday 01 June 2007, I.Reitz wrote:
> then use the tool "Ion Chamber"
> put in Kr (only one gas), 10cm pathlength, 760 Torr, 30000 eV

Hi Irmi,

In addition to everything that Matt said, there is another important
issue that you need to consider if you are looking at the interaction
of high energy photons with gases -- the mass energy-absorption
coefficients, which takes into account the energy deposition in the
gas to Compton recoil electons.  I think this is the proper reference: 

  http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html

Hephaestus makes a lousy attempt to approximate this effect that is
better than doing nothing, but is certainly not correct.  Doing a
proper job of accounting for this effect is more of a computational
challange than seems necessary for a quick-n-dirty beamline tool like
Hephaestus.  Sarvjit Shastri and Jonathon Lang here at the APS have,
as I understand, looked at this carefully in order to characterize the
high energy behavior of APS undulators.

B

-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

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