# Scoring of equivalent dose for decay of multiple radionuclides

Dear FLUKA community,

I am working on the simulation of activated concrete structures to determine the resulting dose equivalent rate.
At the moment I am simulating just one nuclide at a time and correcting the FLUKA results with the total activity for the specific nuclide and the volume of each bin.
H*(10) = H(FLUKA) * A * 3600s/h / V(bin)
I am using the RADDECAY semi-analogue mode and the DOSE-EQ setting for the USRBIN card.

I would now like to simulate multiple nuclides decaying in one run. Setting up a source that switches between different nuclides seems to be no problem. But I am not sure, if my intended way of correcting the scored dose is correct.

A Testcase (
Simulationfiles.zip (8.0 KB)
):
Lets say I am examining the nuclides Co-60 (25% of total activity), Ba-133 (50% of total activity) and Eu-152 (25% of total activity). The different activities are taken into account by the way the nuclides are selected.
Each nuclide in this basic testcase has one specific 2cm2cm2cm water volume assigned: Co-60 around (-10,0,0) , Ba-133 around (0,10,0) and Eu-152 around (10,0,0). Around (0,0,0) there is a 6cm*6cm copper rod.
Simulating 3200000 primaries in total yields the following plot for the dose.

This is the basic result by FLUKA without any correction applied.

My idea of correcting the results to dose rates would be to multiply by the total activity of all three nuclides:
H*(10) = H(Fluka) * Activity(Co+Ba+Eu) * 3600s/h / V(bin)
But I think this can only be the correct way, if the correction from fluence to dose is done after each primary and only not after a full run.

The question I am left with: At what point does the convolution of fluence and correction coefficients happen in FLUKA? Individually for each primary or only after every run?

Hello, thank you for your question.
I will have a closer look as soon as possible.

Best regards,
Tommaso

Dear Tim,

• Fluence-to-dose conversion coefficients are applied at scoring time.

DOSE-EQ, that you are scoring, is a FLUKA generalized particle. Its assessment relies on fluence scoring and uses several sets of fluence-to-dose conversion coefficients (units: pSv cm^2). These coefficients allow to translate radiation fields into the desired quantity.

The two lectures on radiation protection calculations (beginner and advanced) offer insights into fluence-to-dose conversion coefficients. The Manual, instead, contains the list of the generalized particles.

• A USRBIN is configured to score the generalized particle DOSE-EQ. As no other specifications are provided, the default set of conversion coefficients (AMB-74) is applied.
• You are scoring DOSE-EQ in a Cartesian mesh; in this case, volume normalization is automatically applied (this would not be true for a region-based USRBIN). The radiation protection calculation lectures (mentioned earlier) provide guidance on USRBIN scorings for this case (normalization, mesh granularity)
• Please, double check your source routine; I am encountering a compilation error.
• (Minor detail) Currently, you are not assigning the 25-50-25 weights to the three different radionuclides, but rather 1/3, 1/3, 1/3 (set via the SOURCE card).

Wishing you success with your simulation.

Best regards

Tommaso

2 Likes

Dear Tommaso,