Dear Fluka users,
I would like to compute Air Kerma with a polychromatic Xray source, with mean value of 20keV.
I saw in a previous topic that the EMFCUT e- value for transport should be as high as possible, so I entered 28keV. It means that the energy of electron is instantly deposited once created. My question is: What should I enter for prod cut? Does the binning matters for a good air-kerma scoring?
My current values:
EMFCUT -2.7E-05 1E-6 BLKBODY @LASTREG
EMFCUT -1E-05 1E-6 1E-5 BLCKHOLE @LASTMAT PROD-CUT
if you want to score KERMA and not ABSORBED DOSE, the electron and positron cut-off threshold should be set to a large value (just below the maximum energy of your source) in the regions where you want to score.
Correctly as you said, at each photon interaction, the electrons/positrons produced are stopped at the production place and their energy is deposited locally (so what you score is the Kinetic Energy of the charged particles Released in MAtter, i.e. the KERMA).
PROD-CUT you set the delta ray production threshold. If the production threshold is lower than the transport threshold, CPU time is wasted in producing delta rays and dumping them on the spot: you could then enter the same value that you have as transport threshold
As far as the binning is concerned, since you want to estimate kerma you can allow yourself to have a coarser binning: ideally the bin size should be greater or comparable to the range of electrons at cut-off .
For more details you can have a look at this lecture on electromagnetic interactions and at this page for quick estimates on electron ranges.
Dear @dbozzato , in this regard, I have one query regarding the setting a large value (just below the maximum energy of your source) as electron and positron cut-off threshold.
If KERMA is estimated using USRTRACK or USRBDX card by scoring fluence and then later on converting it to KERMA using published fluence to KERMA conversion factor, in this case, do we still have to set electron and positron cut-off threshold as maximum?
Or if we use USRBIN card to score energy and then converting it to KERMA by dividing USRBIN energy output with the mass of the detector, then only we have to set electron and positron cut-off threshold as maximum?
Dear @riya, if you score fluence spectra and later fold them with fluence to kerma conversion coefficients, it would make sense to me to set the thresholds to a value which is just below the lowest tabulated energy value that you have.
If you use USRBIN, be careful that when you score ENERGY the result is in GeV/cm3 so you would have to divide by the density, not the mass. To avoid any normalization you can score directly DOSE (always keeping the thresholds to a high value).