SCINTILLATION MONOCRYSTALS OF KDP:Tl AND KDP:Ce DOPED BY THALLIUM AND CERIUM FOR SELECTIVE DETECTION OF FAST NEUTRONS

Abstract

This research is going to explain the fast neutrons and gamma radiation registration by the new inorganic single crystals of the KDP (Potassium Dihydrogen Phosphat) group that was grown from the water solutions and activated by the thallium Tl+ or cerium Ce3+. The appearance of the luminescence upon KDP:Tl crystals irradiation with the fast neutrons is explained by secondary ionizing radiation (recoil protons and oxygen recoil nuclei) with excitation of the activator under ionization losses for inhibition. Also the recombination mechanism with the radiation defects of the hydrogen sublattice going to transmit electron excitations to the region of the Tl+ luminescence center. In the KDP:Ce crystals the excitation mechanism of the activator has a similar character, but the luminescence itself is due to the 5d ® 4f transition in Ce3+ ions. The detection efficiency for activated KDP:Tl and KDP:Ce crystals to the fast neutrons in comparisons with organic (plastic) scintillators were calculated theoretically and experimentally. For the crystal volume about 10x10x10 mm3 with the optimal activator concentration the fast neutron detection efficiency under irradiation of 239Pu-Be is 12% for KDP:Tl and 16% for KDP:Ce, which is in a consistent with the theoretical calculation and is not lower according to the parameters of typical organic scintillators. A high natural selectivity of the KDP scintillators to the fast neutrons due to their low sensitivity to gamma radiation was detected. Herewith the internal discrimination of n/γ signals (the ratio of detection efficiencies for the fast neutrons and gamma quants) for activated KDP crystals is 7-8 times higher than of regular plastic scintillators.