| Popis: |
The detection of neutron emission arising from conditioned radioactive waste is a nondestructive assay method for the determination of transuranic and fissile material. Active and passive neutron interrogation have to be distinguished. The passive system developed in this dissertation consists of a neutron counter tube embeddedin a moderator to increase the efficiency and to reduce the room background. It detects the neutrons emitted from the object of interest. In the centre of a 2001 concrete filled waste drum the detection limit is below 60 mg reactor grade plutonium. For active neutron interrogation, the low-energetic neutrons from an external source irradiate the object of interest and induce fissions. The fission and source neutrons are separated by there different transport properties due to the difference in energy. The fission neutron signal correlates with the content of fissile material in the object of interest. The Sb-Be photo-neutron source and for the first time for this purpose the Li(p,n,)Be accelerator reaction are used as neutron sources. In the centre of a 2001 concrete filled drum the detection limits are 160 mg $^{235}$U and 50 mg $^{235}$U for the Sb-Be neutron source and the Li(p,n)Be reaction used for neutron production respectively. The detection limit of a system for small samples up to 250 ml is below 40 $\mu$g $^{235}$U. |
