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Forum: Hadronic Processes
Re: Question Understanding format of G4NDL data library (Zach Hartwig)
Date: 19 Dec, 2011
From: Liam Russell <Liam Russell>

Like Zach, I also need to understand the format for the G4NDL final state data files so that I can more easily verify my code against MCNP. To verify my code in GEANT4 against MCNP, I want to convert the MCNP data for several isotopes into the G4NDL format. I would then use this data instead of the stock data files so that both codes have the same input distributions/parameters. Any differences in results would then be a product of either my code or the base GEANT4 algorithms (or both).

The cross section files in the G4NDL libraries are easy to understand and replace, but the final state data is not. The data includes headers, but the main identifiers in these headers may be repeated in a single file with different meanings. For example, a 1 followed by a 5 denotes the prompt neutron energy distribution, and then if repeated before the next major section, it means that the prompt neutron energy distribution is created from the G4NeutronHPEvapSpectrum class. Unfortunately, the minor and major headers seem to be indistinguishable.

To make matters worse, the progress of GEANT4 as it reads through a data file is hard to track in the code since file stream pointer is passed between several classes. Reading the input files starts in the G4NeutronHP______FS files where the blank could be Fission, Elastic, Inelastic or Capture, but it is passed on to several other (sub)classes. Thus, trying to reverse engineer the format from the code is tedious at best. It should be noted that the fission and inelastic final state data is the most complicated, whereas the elastic and capture final state data is relatively simple.

It would help me greatly if someone could provide the documentation to the G4NDL format. Failing that, some tips on the organization of the files and how to read them would be appreciated. Additionally, I agree with Zach that many GEANT4 users would benefit from the documentation of these formats.

Thank you,

Liam Russell
M.Sc. Student, Nuclear Engineering
McMaster University

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