Neutron flux too big

User Support
1

Hello everyone,

I am trying to model the neutron flux through a spherical layer of steel. Right at the end, the tally values are put into a text file. I don’t know if something is wrong with the tallies, but the total flux is unexpectedly large as it is expected to be something smaller than 1. Can anyone see why that is? I have attached the code.

Thanks

Sophia

Simple Model.py (4.14 KB)

2

HI Sophia,

One should not expect the flux to be less than one because the units are particles-cm per source particle. There are specific scores where you can reason about what the value should be. For example, if you tally ‘absorption’ in a problem with no leakage, it should be right around one because every neutron has to get absorbed somewhere.

Best,
Paul

3

Hi Paul,

Thanks for your advice. However, I don’t think the total flux is meant to be higher than 1 either, right? For the model I get a total flux of around 17 neutrons per cm2 per second.

Thanks

Sophia

4

You didn’t consider the conversion factor. All tally scores are normalized per source particle. The unit of flux tally is [ n.cm/source ]. For a better idea, see the following two links.

latest docs & Normalized tally