Neutron spectra in the STEK facility, determined with the SAND-II activation technique

The coupled fast-thermal critical facility STEK, designed for reactivity worth measurements of fission product samples, has been operated with five standard cores with different central neutron spectra. For three standard cores the neutron spectrum in the central oscillator element was also determined with a series of activation and fission foils using the SAND-II program for spectrum unfolding. Results of the neutron spectrum determinations are presented in the ABBN group structure, together with the results of a Monte Carlo error analysis considering the effects of variations in the input spectrum, of measurement errors in the input activities, and of uncertainties in the cross section data