| M.Gmar, S.Boyer, E.Berthoumieux, F.Carrel, D.Doré, M-L.Giacri, F.Lainé,B.Poumarède, D.Ridikas, A.Van Lauwe |
Photons with energies above 6 MeV can be used to detect small amounts of nuclear material
inside large cargo containers. The method consists in using an intense beam of high-energy
photons (bremsstrahlung radiation) in order to induce reactions of photofission on actinides.
The measurement of delayed neutrons and delayed gammas emitted by fission products brings
specific information on localization and quantification of the nuclear material. A simultaneous
measurement of both of these delayed signals can overcome some important limitations due
to matrix effects like heavy shielding and/or the presence of light elements as hydrogen. We
have a long experience in the field of nuclear waste package characterization by photon
interrogation and we have demonstrated that presently the detection limit can be less than
one gram of actinide per ton of package. Recently we tried to extend our knowledge to assess
the performance of this method for the detection of special nuclear materials in sea and air
freights. This paper presents our first results based on experimental measurements carried
out in the SAPHIR facility, which houses a linear electron accelerator with the energy range
from 15 MeV to 30 MeV. Our experiments were also modeled using the full scale Monte Carlo
techniques. In addition, and in a more general frame, due to the lack of consistent data on
photonuclear reactions, we have been working on the development of a new photonuclear
activation file (PAF), which includes cross sections for more than 600 isotopes including
photofission fragment distributions and delayed neutron tables for actinides. Therefore,
this work includes also some experimental results obtained at the ELSA electron accelerator,
which is more adopted for precise basic nuclear data measurements. |
