High-sensitivity detection of fissile materials in a waste dram by direct interrogation of 14MeV acc neutrons

Through the studies of active neutron method to detect fissile materials in a radioactive waste drum, the effectiveness of a new method in which 14MeV neutrons directly interrogate the waste drum was found out, and thus probl ems of conventional active neutron method such as its week sensitivity to t he center portion of the waste drum seem to be solved. The new method is ba sed on the moderation of 14MeV neutrons, emitted from an accelerator tube, to thermal neutrons in the matrix of waste drum itself and the detection of fast neutrons from nuclear fission induced by those thermal neutrons in th e waste drum. Experiments and theoretical analyses showed capability of the new method to increase remarkably the detection sensitivity to fissile mat erials existing in the center portion of waste drum. Namely, the order of d etection sensitivity difference over 100 times along the radial direction i n the waste drum with the conventional method can be decreased to about +/- 18% with the new method. The difference in the whole drum body is only abou t +/-22%, and Pu of 30mg in the center portion of drum can be detected and the detection limitation level is 4-5mg. Because all those data were obtain ed with a measurement setup that was designed for the study with convention al active neutron method, one could obtain more better results with an opti mum measurement setup suited to the new method.