Energy Filter and Material Filter Combined

User Support
1

Hi All,

I am currently trying to create a Tally to measure the energy of the incident neutron of a (n,T) reaction. I currently a Tally create like this:

    material_filter  = openmc.MaterialFilter(Blanket_Layer_mat)
    energy_filter = openmc.EnergyFilter.from_group_structure('CCFE-709')

    tbr_tally = openmc.Tally(name=('TBR'))
    tbr_tally.filters= [material_filter, energy_filter]
    tbr_tally.scores = ['H3-production']
    tbr_tally.nuclides = [openmc.Nuclide('Li6'), openmc.Nuclide('Li7')]

The material filter can be imagined like two cubes of material inline with the source with one infront of the other. Now in the documents the energy filter is described as: ‘Bins tally events based on incident particle energy.’ . My question is in this case would the energy of the neutron be tallied upon entering the material of the material filter or upon creation of the H3 i.e. is the energy of the neutron the energy it entered the material at or the energy of the neutron upon create of the Tritium

Adam

2

The energy filter allows you to determine the score of interest (in your case tritium production) as a function of incident neutron energy. So, every time a contribution is made to the H3-production score, the contribution is placed in the energy bin corresponding to the energy of the neutron. Note that generally speaking this score is not analog, meaning the code is not literally keeping track of individual atoms of tritium being produced. Rather, there is a tritium production cross section that is produced by NJOY and the score simply takes the flux and multiplies it by that tritium production cross section. This means that scores can be made using either a tracklength or collision estimator.

3

Thanks for the reply.

Yes this makes sense as the product of the Scalar Flux and Cross section would give you the reaction rate. May I ask what is the default estimator for scores?

4

OpenMC will always try to use the tracklength estimator unless specified otherwise or if there is a particular filter/score that requires a different estimator (e.g., the EnergyoutFilter requires a collision estimator).