Spectral characterization of the NISUS neutron field

Information on the central neutron spectrum of the standard neutron field NISUS consists of proton recoil proportional counter data, 6Li solid state sandwich spectrometry data, fission rate ratios obtained using NBS-type fission chambers and activation foil data. In addition it is known that the NISUS spectrum closely resembles that of Mol-ΣΣ. In this paper these data are briefly reviewed and a recommended evaluated spectrum is presented. The evaluation was performed by means of the code SIMMM which simultaneously evaluates spectra, reaction rates and dosimetry cross-sections. The fit between the spectrometry data, reaction rates and ENDF/BIV dosimetry data was very good. The SIMMM code does not produce any evaluations of errors, but these are subjectively estimated as +-5% for the recommended spectrum in the energy range 67.4 keV - 7.41 MeV, and +-20% outside this range. (author)