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Watt parameters for the Los Alamos Model : Subroutine getab

Many neutron transport Monte-Carlo codes can randomly sample fission neutron energies from a Watt spectrum. The quality of simulations depends on how well the Watt spectrum represents the true energy spectrum of the fission neutrons, and on one's choice of the Watt parameters a and b. The energy spectra of fission neutrons have been calculated and tabulated for the neutron induced fission of 235,238U and 239Pu as a function of incoming neutron energy by Madland using the Los Alamos Model. Each of these energy spectra are mapped into time-of-flight space and fitted with a Watt spectrum. A subroutine getab has been written to interpolate these results, so that Watt a and b parameters can be estimated for all incoming neutron energies up to ~16 MeV.