Characterization of Ionizing Radiation Generated from Interaction of High-Intensity Laser with Matter

Abstract

Technological advances allow an increasing number of facilities around the world to install high-power multi-terawatt and petawatt lasers. These high-power lasers can be focused to high-intensities greater than 10^17 W cm^-2 onto target materials to study matter at higher pressures and temperatures. The interaction of a high-intensity laser with matter in vacuum creates a plasma layer on the surface of the target. Additional interactions between the remainder of the laser pulse and the plasma can accelerate electrons in the plasma up to tens and hundreds of MeV in energy. These “hot” electrons escape from the plasma and interact with the target material and the target vacuum chamber walls and generated bremsstrahlung photons, which can pose an ionizing radiation hazard for personnel working near these laser facilities if radiation shielding is insufficient. Identifying the relation between the laser-plasma interactions and the magnitude of the radiation yields are crucial in developing radiological controls for high-intensity laser facilities. The particle-in-cell (PIC) method plasma code EPOCH can simulate the laser-plasma interactions and characterize key parameters of the hot electron source term, including the energy distribution, angular distribution, and laser-to-electron conversion efficiency. The Monte Carlo radiation transport and interaction code FLUKA can utilize EPOCH's hot electron source term to calculate the bremsstrahlung photon yields at various angles. A systematic study from coupling EPOCH and FLUKA to develop a bremsstrahlung dose yield source term as a function of laser intensities between 10^17 and 10^22 W cm^-2 is presented, and comparisons with measurement data are also made.