DETERMINATION OF NEUTRON SPECTRUM BY THE DOSIMETRY FOIL METHOD UP TO 37 MEV

The dosimetry activation foil technique was used for the determination of a white neutron spectrum at the UI20M cyclotron facility of NPUReZ. The neutrons were produced by 37 MeV protons slowing down in the thick heavy water target and have an energy distribution extending up to 37 MeV. To cover the whole energy range a set of 10 foils AI, Ti, Fe, Co, Ni, Y, Nb, In, Lu, and Au was used. The y-rays ITom the decaying nuclei produced in 26 activation reactions were detected. The cross sections for these reaction were chosen ITom European Activation File EAF2007 (up to 55 MeV) after intercomparison with the dosimetry cross section library IRDF-2002 which represents the cross section only up to 20 MeV and other high energy libraries. For the spectrum determination the SAND-II code was used after it had been modified to input dosimetry cross sections above 20 MeV in an arbitrary group structure. The guessed neutron spectrum which is needed to start an adjustment procedure was combined ITom those measured and calculated by the MCNPX code. The uncertainty of the adjusted neutron spectrum was estimated using the uncertainties of measured specific y-activities induced in nuclides and dosimetry cross sections. It is less than 10% in the energy range below 25 MeV, the sensitivity domain of the most dosimetry reactions, but increases above this energy.