Transport Thresholds and Absorption Coefficients for Optical Photons Simulation

I wish to understand the spectrum and distribution of Cherenkov radiation of a 185 MeV proton pencil beam traveling through a cube of water.

Also, I am learning of the importance of the relation between the right transport and production thresholds and the bin size of the scoring.

My question are:

  1. If a delta ray is produced, will FLUKA generate Cherenkov radiation from that secondary particle?

  2. Since I have read that approximately 0.1% of the energy of the protons should be emitted as radiation, what is the optimal way to set the thresholds in the DELTA RAY and EMFCUT cards and bin size in USRBIN and USRYIELD?

  3. How could I set the absorption coefficient of water to be dependent on wavelength?

Dear @Sergio_Leon,

Delta rays produced as secondary particle will generate Cherenkov radiation provided their velocity is high enough and you have activated Cherenkov radiation in the material.

Regarding the appropriate cuts for your simulation, you should aim to have the range of secondary electrons and photons similar or smaller to the size of your bins. I suggest you consult the NIST estar database to get an idea of the ranges you could expect given an energy cutoff. Note that the DELTA-RAY and EMFCUT have similar effects. The difference is the DELTA-RAY card only applies to secondary electrons from charged hadrons and muons while the EMFCUT card applies to photons and electrons from all processes.

To set an absorption coefficient dependent on the wavelength you could use the user routine RFRNDX. To activate calls to the routine, the absorption coefficient in the OPT-PROP card must be set to less than -99. For example:


You could also define the derivatives up to the third order using the OPT-PROP card with the SDUM blank, &1, &2 and &3. For details on how to proceed please refer to note 2 of the manual on the OPT-PROP card.

Thank you for the quick reply!