Neutron selfshielding of activation detectors used in spectrum unfolding

Neutron selfshielding corrections for activation detectors have been studied with a computer program SELFS which is used in combination with SAND-II, the computer program for determining neutron spectra with the aid of a set of irradiated foil detectors. The method does not apply integral correction factors to the measured activities but applies energy dependent correction factors to the group cross section values. This calculation method has the advantage that correction can be calculated only once for a given foil thickness and can be applied to each neutron spectrum with known shape. The applied formula to calculate the selfshielding is valid under limited conditions but in practice the elementary formula provides data which are accurate enough. The results of calculations have been compared with literature data (e.g., for a 1/E neutron spectrum, and for the neutron spectra of the ΣΣ facility in Mol and CFRMF in Los Alamos). The cross section data required were taken from the SAND-II, ENDF/B and the BNL-325 data sources. The program SELFS is written in FORTRAN and was used on a CDC-6600 computer