Difference in USRBIN output with different quantities scored

Good afternoon Experts,

I am attempting to solve a basic problem of evaluating the exposure rate at 1m from 1 Ci (RHM) Co-60 source.

The following Runs are done:
With and without EMFcut ; (Ref. : Strange Pattern in USRBIN-DOSE Scoring Result - #7 by fogallar )
Scored Dose Eq, Dose and Energy;
USRBIN = Cartesian binning, 8 cc bin volume at 100 cm

PFA the input files.(The input is RUN for without any thresholds applied and with low thresholds in EMFcut card applied.)

Co_1.inp (2.1 KB)
Co_1_21.bnn.lis (4.9 KB)
Co_emfcut2.inp (2.2 KB)
Co_emfcut2_21.bnn.lis (4.9 KB)

Ques: i) Using normalization factor (N.F.) = 26640 for converting pSv/primary to R/h, we get a value close to 1.32 R/h (theoretical value, RHM is R/h at 1 m- gamma ray constant). Can we score DOSE Eq for this purpose?

ii) For DOSE scored, N.F. = 4.8669E09 for converting GeV/g to R/h, we get a value half of that obtained with DOSE EQ scored. Is this wrong? N.F. uses Gy to rad to R conversion factors.

ii) For ENERGY scored, N.F. = 4.0332E12 for converting GeV/cc to R/h. This value is close to that obtained with DOSE scored.

RHM obtained with DOSE and ENERGY are not close to 1.32 R/h. (Calculated values are shown in the screenshot)

As Dose and Dose Eq are related by radiation weighting factor, which is 1 for gamma and electrons, shouldn’t we obtain the same values of RHM by scoring DOSE & DOSE EQ ?

Kindly guide on this.

Thanking in advance, with regards,
Raksha Rajput.

Good morning Experts,

To add one detail to my previous post:
Please note that in the screenshot, the first 2 rows show the data for “without EMFcut” used and the next 2 rows are results with EMFcut threhsolds used.

Raksha Rajput.

Dear @raksha,

Without EMFCUT, the transport thresholds for e+/- and photons are 100 keV: for your purposes I would suggest at least to lower the thresholds to at least 10 keV since low energy photons can contribute to the effective dose.

As you for sure know, Co-60 has two prominent lines: instead of simulating monoenergetic photons with the average energy of the two, you should properly simulate the decay of Co-60 isotopes by changing the particle to ISOTOPE in the Beam card, adding the HI-PROPE card and RADDECAY as in the example attached below. The output is then conveniently expressed per primary isotope (Co-60) decay.

Do not mix the different quantities. It really depends on what you ultimately need:

  • DOSE scores energy deposition in GeV/g
  • Energy, the energy deposited in GeV/cm3 (dividing by the air density you get the previous)
  • DOSE-EQ, by default, scores Ambient Dose Equivalent H*(10) using conversion coefficients from ICRP 74 and M. Pelliccioni. In short it is related to an energy deposition but at 10 cm in the ICRU sphere, hence the possible difference. Other sets of conversion coefficients are available via the AUXSCORE card (see again the attachment) but I remind you that Effective Dose is defined as the sum of the weighted equivalent doses HT in all tissues and organs of the human body and in turn HT is the weighted sum of the average absorbed dose from all radiations in the tissue. So there is not simply a radiation weighting factor between the two.

I hope this helps,

PS: Since you simulate a point source, you can conveniently use a R-Phi-Z scoring mesh.
co60.inp (1.8 KB)

Good evening Davide,

Thank you very much for the explanation and the input file.
I shall surely attempt it with ISOTOPE in Beam for a point source.

What do you suggest for cylindrical multiple number (say 25 nos.) of Co-60 sources in the same input? In that case, Beam=ISOTOPE input will work efficiently or 2 photon energies should be given using source.f, along with the multiple position co-ordinates?
Kindly suggest.

Thanking in advance, with regards,

Dear @raksha ,

if you use ISOTOPE you do not have to use the source routine: the gamma energies will be sampled by FLUKA.

I don’t exactly understand what you mean by ‘cylindrical multiple number’: in case you wish to have a spatially extended source (see the BEAMPOS card), ISOTOPE will perfectly work as well and the sampling of the radionuclide coordinates inside the source volume will be done by FLUKA.


Dear @dbozzato,

Thank you for this insight.
Yes, the source is an extended source, cylindrical in shape (length = 40 cm and 0.6 cm diameter). Then, I also intend to use no. of sources arranged in a rectangular pattern for which the co-ordinates will be given in source.f. (If it were a single cylindrical source, I would have used CYLIN-VOL, but there are more than one source).
(And now I understand, if I use ISOTOPE, I don’t have to specify energies in source.f.)

Thank you again, with kind regards,

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