The physics and validation of the Cygnus radiographic source for Armando

Summary form only given. Conventional simulation techniques for radiographic systems use approximations that poorly represent the dynamics of the electron beam that generates photons via the bremsstrahlung process. The radiographic chain model more accurately accounts for the electron dynamics by linking electron distributions generated in electromagnetic particle-in-cell (PIC) simulations in a self-consistent way to the Monte Carlo particle transport code MCNP. Based on the electron dynamics from PIC simulations, MCNP simulates the emission of bremsstrahlung photons due to the electron collisions with a dense target in the radiographic source and then calculates the photon transport through the imaging object onto the detectors, which are simulated with detector response functions. This integrated radiographic simulation capability has been applied in understanding the Cygnus source physics, and is validated in conjunction with the performance of the Cygnus radiographic machine, which is being used in a dual-axis configuration in the sub-critical experiment Armando. We used the two-dimensional, time-dependent, fully electromagnetic relativistic PIC code MERLIN to simulate the Cygnus rod-pinch diode. By employing the methodology of the chain model, we characterized the effect of the rod-pinch diode operating parameters (e.g., voltage, current, anode-cathode aspect ratio, anode material and radius) in the Cygnus radiographic-machine parameters, such as energy-and angle-dependent photon spectra, spot size, and dose. The calculations were validated in juxtaposition with radiographic experimental data on step wedges, rolled edges, and static objects. We present the physics principle of the rod-pinch driven radiographic source and the detailed characterization of the performance of the Cygnus source for Armando.