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Report No.
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Improvement of detection limit in differential die-away analysis system for nuclear non-proliferation and nuclear security

Ozu, Akira; Maeda, Makoto; Komeda, Masao; Toh, Yosuke  

In the fields of safeguards, nuclear non-proliferation, and nuclear security, non-destructive analysis (NDA) techniques useful for highly radioactive nuclear materials (NMs) are not established yet because there are so many technical difficulties to measure the amount of the highly radioactive NMs. A novel NDA system with a pulsed neutron source as the method for determining the composition of mixed NMs has been developing in the Japan Atomic Energy Agency. In the NDA system, a differential die-away analysis (DDA) technique is used to quantify the amount of fissile materials. The detection limit of fissile materials in DDA system is determined by the signal to noise ratio in fast neutron counting. A method to reduce the noise signal by using neutron absorber (B$$_{4}$$C rubber) sheets mounted on the inner entire surface in the sample cavity is proposed. The effect of the sheets on the reduction of noise signal in the fast neutron counting was investigated in both experimental test and simulation. The experimental results show that it is possible to detect a nuclear fissile material ($$^{239}$$Pu) of as low as 1 mg in a vial bottle when the absorber sheets with a thickness of 3 mm is used. This paper also presents comparison between experimental data and simulation results.

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