Hello Everyone,
In OpenMC, the flux unit is particles/(cm² · source particle), whereas in MCNP, it is particles/cm²/s. To match the unit in OpenMC to that of MCNP, can we multiply the OpenMC flux by the source strength (where the source strength = number of particles per batch × number of batches / total simulation time)
Would this method be correct?
Thank you!
Best regards,
Hasan Ghotme
8. Specifying Tallies — OpenMC Documentation
Yes, this conversion procedure is described here.
No - this is not correct. Your actual source strength is entirely independent of the number of particles per batch or number of batches. This is a common misconception.
Your actual source strength is an external quantity that you must know about your system. If you are simulating a reactor, it will be related to your reactor power. If you are simulating a fixed source, it will be related to the strength of that fixed source. OpenMC has no way to know what this value is, so it reports results normalized to each of those source particles. You will need to multiply your results by the number of source particles per second in your real system to get physical units.
Note: this is not different from MCNP.
Hello Mr. Gonuke,
Thank you very much for your response! Actually, I was lost with the point detector…
I have a quick question, please: Since OpenMC does not have an F5 point detector, how can we estimate it? Considering that the F5 unit is particles·cm⁻²·source⁻¹, while the flux is particles·cm⁻²·s⁻¹, can we calculate the equivalent of F5 in OpenMC just by dividing the flux by the source strength?
The F5 tally estimates the flux at a specific point, so I used a very small volume around the detector, but the physical measurement is in particles·cm⁻²·s⁻¹