Time-Dependent Monte Carlo Deposition Rate from Flash X-Ray Sources

We present a scheme for obtaining a continuous and explicit time-dependent description of the transport of all generations of particles in the cascade produced by state-of-the-art coupled electron/photon Monte Carlo codes that employ a macroscopic random walk to describe electron trajectories. The model is applied to the prediction of the time-dependent energy deposition rate in air exposed to the flash x-ray environment generated by a high-intensity pulsed relativistic electron source with energies up to 10.0 MeV. Results obtained for an instantaneous pulse demonstrate the time dispersion, or transport broadening, of the deposition rate due to the scattered x rays. The magnitude of the delayed contribution from this scattered radiation is predicted for a source based on synchronized half-sine-wave voltage and current pulses. The spatially dependent time-integrated deposition is verified through comparison with the volume-averaged deposition predicted by a time-independent model.