New Evaluation of the 232Th Neutron Resonance Parameters in the Energy Range 0 to 4 keV

The neutron resonance parameters of 232Th were reevaluated in the energy range 0 to 4 keV from a Reich-Moore SAMMY1 analysis of the most recent experimental neutron transmission and neutron capture data. The experimental database was formed mainly by the transmission measurements performed at ORELA by Olsen et al.2 in 1980, the effective capture cross section measurements performed at GELINA by Schillebeeckx et al.3 in 2002, and the effective capture cross section measurements performed at nTOF by Aerts et al.4 in 2003. The previous evaluation was performed by Olsen5 for ENDF/B-VI in 1981. The evaluation by Olsen was not intended to be a comprehensive study. Olsen used smooth background cross sections to compensate for the inadequacy of the resonance parameters to reproduce the totality of the cross sections. The present evaluation brings important improvements concerning the following points: 1 / Two recent high-resolution effective capture cross section measurements (Geel and nTOF) were available for the present evaluation. By taking advantage of the ability of SAMMY to accurately calculate the multiple-scattering effects in the thorium samples, we were able to calculate the average capture cross section to better than 3 % accuracy. 2 / In the energy range 1.0 eV to 10 eV the new resonance parameters reproduce the experimenta