| Popis: |
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 problems of conventional active neutron method such as its week sensitivity to the center portion of the waste drum seem to be solved. The new method is based 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 the waste drum. Experiments and theoretical analyses showed capability of the new method to increase remarkably the detection sensitivity to fissile materials existing in the center portion of waste drum. Namely, the order of detection sensitivity difference over 100 times along the radial direction in 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 about ±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 obtained with a measurement setup that was designed for the study with conventional active neutron method, one could obtain more better results with an optimum measurement setup suited to the new method. |
