46 / 2020-02-03 20:03:42

Feasibility of a laser-driven gamma-ray source for active interrogation of special nuclear materials

laser-driven gamma-ray source,active interrogation,special nuclear materials,19F(p,α gamma)16O reaction

全体主题 > 极端条件下的物理学

Active interrogation represents the most promising detection technique in combating illicit trafficking and diverted use of special nuclear materials (SNM) such as highly enriched uranium and plutonium. Active interrogation excites nuclei in a target by either neutrons or gamma-rays, and looks for radiation signatures (neutrons and/or gamma´s) emitted by the target materials. Among the many interrogation approaches under investigation, the one based on photoinduced fission relies on large prompt and delayed radiation signatures. Pulsed induction (tens of ns) of photofission, in particular, enables to distinguish between prompt and delayed radiation emission, providing additional signatures to identify fissile materials. As the probing radiation, 6 to 7 MeV characteristic -rays produced by the 19F(p,α gamma)16O reaction are of particular interest; indeed, they have energy sufficient to induce fission in SNM, but insufficient to create significant radioactivity via photonuclear activation, especially in lighter elements. Besides the reduced impact from the radiation protection standpoint, this feature also provides the technique with additional discrimination capability between SNM and surrounding ordinary materials.
In this study, the feasibility of a pulsed source of characteristic gamma-rays based on the interaction of laser-accelerated protons with a fluorine-rich secondary target is assessed, with particular emphasis on SNM active interrogation. As has been widely demonstrated in the last years, the interaction of ultrahigh-power laser beams (intensity of the order of or higher than 10^19 W cm^-2, sub-ps duration) with thin foils (1÷100 μm thickness) is able to produce well collimated (<10º), ultra-short (few ps) bunches of protons with energy ranging from a few MeV up to several tens of MeV. For applications to SNM pulsed interrogation via the 19F(p,α gamma)16O reaction, proton energies above 2 MeV, a bunch population of at least 10^14 particles, and a repetition rate of the order of 10 Hz are of interest. The development of ultrahigh-power table-top lasers could greatly contribute to the deployment of this kind of interrogation source for a variety of operations (e.g., remote inspection of containers standing in airports and harbours, or moving on means of transport).