|Program name||Package id||Status||Status date|
|Package ID||Orig. computer||Test computer|
|NEA-0914/08||PC Windows||PC Windows|
REFIT carries out fits to measured neutron cross-section data, by adjusting the nuclear parameters used in the multi-level R-matrix formalism as well as experimental parameters. The adjustment of the parameters is continued until the calculated transmission and/or reaction yields from neutron Time Of Flight (TOF) measurements agree with the observed data within the limits of the measured uncertainties. In its present form it can perform simultaneous fits on up to 30 sets of measured data. The data sets can be of different types, refer to different target sample thickness and refer to different sample isotopic composition. The types of measurement include transmission and the reaction types:- capture, fission, scattering and self-indication. The output gives details of the analysis and all the fitted parameters with their uncertainties. The code also outputs a new list of resonance parameters in ENDF6 format suitable for putting in an evaluation file.
The nuclear cross section for each nucleus is calculated from initial parameters using an R-matrix multi-level formalism. The cross section is then Doppler broadened using either an ideal gas model or Moxon's simple Phonon Model, or Meister's Einstein Crystal Model, or Naberejnev's Harmonic Crystal Model. Some of the parameters associated with the Doppler broadening can be adjusted in the fit e.g. in the gas model the effective temperature. The transmission or reaction yield for a given sample is then calculated from the Doppler broadened cross sections, given abundances of the nuclei and the thickness of the sample in the neutron beam. In the case of reaction data the calculated reaction yield includes the effects of a multiple collision of the neutrons in the sample and the detection of scattered neutrons. The theoretical curves are then folded with the resolution function which can be calculated from parameters that include: - the initial pulse width, the decay of neutrons leaving the source and moderator, etc or from tabulated values. The nuclear parameters are the resonance energies, neutron widths, radiation widths and effective nuclear interaction radii. Provision has also been made to fit experimental parameters such as zero delay, flight path length, background, normalisation, resolution parameters etc. as well as the nuclear parameters.
A modified version of the Harwell computer library minimising routine VA02A is used to obtain the best fit to the data by varying the required parameters, and outputs the parameters at the minimum value of chi-squared. The modified library routine SV01AS outputs the uncertainties (one standard deviation) together with the correlation coefficients matrix. The source of these routines is present with the main source code.
Also contained in the package is the following auxiliary program:
RESCON-2009 converts ENDF format into REFIT format.
|Package ID||Status date||Status|
|NEA-0914/08||27-OCT-2011||Tested at NEADB|
|Package ID||Computer language|
United Kingdom Atomic Energy Authority
Culham Science Centre
M. C. Moxon (lead)
3 Hyde Copse
T. C. Ware, C. J. Dean
Keywords: Doppler broadening, R matrix, capture, least square fit, multilevel analysis, neutron cross sections, neutron reactions, neutron spectra, resolved region, resonance integrals, transmission.