Prompt γ-ray emission in nuclear fission

A challenging task within the modelling of new generation reactor neutron kinetics is the calculation of the γ-heat deposition e. g. in steel and ceramics reflectors without UO2 blankets, which is required to be known with an uncertainty as low as 7.5%. A major difficulty in measuring prompt γ-ray emission in fission is the competition between γ-ray emission and prompt neutron evaporation during fission-fragment de-excitation and the suppression of background γ-rays induced by those neutrons in the γ-ray detector. A common method is to distinguish between γ-rays and neutrons by their different times of flight, which however is limited by the timing resolution of the detector (not better than 5 ns for sodium-iodine detectors). A promising experimental approach seems to be the use of recently developed cerium-doped lanthanum halide crystal scintillation detectors in conjunction with an ultra-fast fission event trigger based on artificial diamonds. This is the report on recent detector suitability studies being carried out at the European Commission Joint Research Centre IRMM, which are dedicated to new and accurate measurements of fission γ-ray data. (author)