Absorbed dose for the x-ray mirror at grazing incident angle and consider the photoelectric effect

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Dear FLUKA experts,

I am new to FLUKA and I am trying to simulate energy deposition distribution.

I have a silicon mirror coated by B4C. The source is an X-ray free electron laser (XFEL) with an energy of 1 keV.
The penetration depth (or attenuation length) depends on the incident angle of the beam, and there is an equation to calculate the penetration depth and then the absorbed dose.

But according to this article:
“London, Richard A., et al. “Computational simulations of high-intensity x-ray matter interaction.” Optics for Fourth-Generation X-Ray Sources. Vol. 4500. SPIE, 2001.”,
At small grazing incident angles (like 9mrad), the penetration of the x-rays into the material is quite small. Because the energetic photoelectron produced by the absorbed X-rays would ballistically transport the absorbed energy over a significantly larger volume and into the surrounding material. It has been written that the only way to calculate this effect is using Monte Carlo simulations like Fluka and Penelope.
So now I want to calculate the absorbed energy ( Dose [eV/atom]) and plot it versus depth and incident angle. To find out under what conditions the mirror is damaged.

  1. To calculate the absorbed dose[eV/atom], USRBIN with part: DOSE should be used?
  2. I can add mirror properties in OPT-PROP card with Type = “blank” for specific energy. Is it correct?
  3. In the interaction of photons with matter, when and how can I simulate and consider the photoelectric effect?
  4. With which option can I calculate energy deposition depth?

I really appreciate your help.

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Good morning Marziyeh,

Considering your very low primary photon energy (1 keV), you will need to add EMFCUT cards to lower the transport and production cuts of electrons and photons from their respective default values of 100 keV and 33 keV (assuming PRECISIOn DEFAULTS) to the lowest values accepted by FLUKA: 1 keV and 100 eV, respectively. Otherwise, the photon energy will be deposited on the spot.

Please refer to the EMFCUT card documentation:
https://flukafiles.web.cern.ch/manual/chapters/description_input/description_options/emfcut.html

1 - To calculate the absorbed dose[eV/atom], USRBIN with part: DOSE should be used?

You can add a USRBIN with either Cartesian or cylindrical mesh (whatever is best adapted to your geometry) and request to score the DOSE. You will then obtain the dose in GeV/g/primary. It is then up to you to convert this into eV/atom with your actual irradiation condition.

2 - I can add mirror properties in OPT-PROP card with Type = “blank” for specific energy. Is it correct?

Indeed. Note, however, that these settings will apply to optical photons, not your 1 keV photons.

If you’re interested in optical photons, you’ll need an OPT-PROD card to specify what’s the fraction of energy deposition available for the production of optical photons, switch on scintillation production, etc. See: 7.22.53. OPT-PROD — FLUKA Manual

You can then use the OPT-PROP card to set the optical properties (reflectivity, refraction index, diffusion/absorption coefficient, etc.) of your materials of interest as per 7.22.54. OPT-PROP — FLUKA Manual

3 - In the interaction of photons with matter, when and how can I simulate and consider the photoelectric effect?

If you use PRECISIOn DEFAULTS, photon interactions (including the photoelectric effect) are automatically enabled, as well as the subsequent fluorescence photon emission.

4 - With which option can I calculate energy deposition depth?

Using the USRBIN card with a Cartesian/cylindrical mesh as felt best, scoring ENERGY, you will be able to spatially resolve the energy deposition distribution (in GeV/cm^3/primary). Once you’ve run your simulation and processed the output files, you can plot the energy deposition as a function of depth with FLAIR using “1D projection” along the appropriate axis.

Cheers,

Jean Baptiste

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Dear Jean,

Many thanks for your kind help.

You wrote, “these settings will apply to optical photons, not your 1 keV photons.” What about x-ray mirrors? If I want to import the refraction index or other mirror properties, which card should I use?

I really appreciate your taking the time to explain things.

Best regards,
Marziyeh

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Good evening Marziyieh,

As it is indicated in the manual : 7.22.53. OPT-PROD — FLUKA Manual
the user routine RFRNDX is available to specify a refraction index as a function of wavelength, frequency or energy. Activated by setting WHAT(1) < -99 when SDUM = blank. (OPT-PROP card), which is what you want to do I guess ?

Best regards,
J.Baptiste

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