Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Abstract:

When a laser pulse of intensity 1019 W cm−2 interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional γ-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, 62,64Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (γ, n) reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in 238U has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the 11C and the 62Cu β+ activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of ∼1019 W cm−2. © 2000 The American Physical Society.