onix.nax.list_NAX_ng_chain_from_output

onix.nax.list_NAX_ng_chain_from_output(path, cell, step)[source]

This function builds chains of nuclides connected via (n,gamma) reactions. These chains will be used to find the best isotopic ratios for fluence estimations.

Detail description: The function builds dictionnaries where keys are atomic number (z) and entries are list of (n,gamma) chains (there can be multiple chains per z number). The elements in the list are tuples where the first element is the name of the nuclide and the second element is its natural abundance. The way chains are constructed is as follows:

  • The algorithm gathers all isotopes of same z which have data in the one-group cross section library of the simulation (nuclides with no cross section data are not considered)

  • Then it removes all isotopes which comes before the first naturally occuring isotopes (in the (n,gamma) chain order)

  • Then it removes all isotopes which are not produced by their (n,gamma) precursor in the (n,gamma) chain

  • Then it removes all isotopes which have half life smaller than 10,000 years (changes due to decay should be negligible compared to changes due to (n,gamma) reactions)

Note 1: Isotopes from a (n,gamma) chain which are produced by other neutron-induced reactions at a rate similar or higher than the (n,gamma) reaction should also be removed. However, since the production rate depends not only on the one-group cross section but also on the density of the precursor, it requires knowing the actual density of the elements present in the material studied. The objective of the NAX module is to identify potential good fluence indicators among all possible isotopes without knowing the actual isotopics of the material studied. Therefore, this criteria is not implemented in the NAX module.

Note 2: All isotopes tested are assumed to be present in the material according to their natural abundance. Absolute density of each element (families of isotopes) does not play a role here as ratios are taken between isotopes of the same elements.

Note 3: In the current version, the user needs to specify a macrostep which will be used by the code to verify the values of the one-group (n,gamma) cross sections. It is reasonably assumed that if a nuclide’s one-group cross section is non-zero at a specific macrostep, it is non-zero all along the simulation.

Parameters

  • path (str) – Path to a simulation’s directory

  • cell (str) – Name of the BUCell to be studied

  • step (int) – Macrostep at which tests on one-group (n,gamma) cross section are to be done