Berkeley Lab

MeV Photon Sources and Nuclear Security Applications

Compact LPAs produce GeV electrons in centimeter accelerating structure lengths, enabling transportable quasi-monoenergetic photon sources

Conceptual diagram of a gamma-ray interrogation system based on a Thomson-scattering source.

Conceptual diagram of a gamma-ray interrogation system based on a Thomson-scattering source.

BELLA Center researchers are developing laser-plasma accelerators (LPAs) to enable compact, collimated, monoenergetic photon sources for special nuclear material (SNM) detection, as well as for nuclear physics studies, via Thomson scattering of laser light off the electron beam. Such sources offer the promise of improved sensitivity at greatly reduced dose for active interrogation, and new capabilities in treaty verification, NDA of spent nuclear fuel and emergency response. Compact, efficient accelerators with low energy spread and emittance in the 0.2-1 GeV energy range are required to drive the photon source.

Monoenergetic photon sources allow SNM signatures to be obtained with greatly reduced radiation doses to the target compared to broadband bremsstrahlung sources. In addition, the narrow energy spread reduces background, improving detection in nuclear resonance fluorescence (NRF) screening, where a very narrow linewidth signal must be detected. The same properties are important for basic nuclear physics studies, including scattering. Small beam divergence offers the potential for high resolution scans or for interrogating targets tens of meters away.

Thomson scattering is a demonstrated source of monoenergetic, low divergence MeV gammas, and requires a ~0.2-0.8 GeV accelerator, scattering laser beamline, and beam stop. To accomplish this with traditional approaches, the rf linac must be tens of meters long to reach the required electron energies, and the scattering lines are themselves several meters long, especially for high-repetition-rate systems; plainly these are large fixed facilities.

BELLA researchers and collaborators are now operating a source based on LPAs that offers a testbed for application experiments, and are developing it as a path toward photon sources of greatly reduced size and increased precision. The source is based on LPAs at the required 0.2-0.8 GeV, which are only one to three cm long. To date, it has been used for experiments demonstrating high resolution radiography,. Experiments on unique signatures that the source enables are in progress. We invite contact from potential collaborators on source development, signatures, applications and detection methods. This work will develop the required techniques for an application-usable LPA based compact gamma source offering increased resolution, reduced radiation dose, and new types of signatures, taking advantage of compact and rapidly developing lasers.