Simulations of Photon Activation of Thin Metal Foils

The Dual-Axis Hydrodynamic Test (DARHT) facility consists of two linear induction accelerators which produce an electron beam at energies between 16 and 20 MeV and currents between 1.6 and 2 kA. Once this beam hits a heavy metal target the bremmstrahlung x-rays produced can be used for photon activation of thin metal foils Zn, Cu, Mo, Ag, and In. From the photon counts and energy peaks of the isotopes, the initial dose on the foils can be calculated and compared to bremsstrahlung theory. We conduct a parameter study using two codes: the DOSECALCX code[1] and MCNP[2]. The DOSECALCX code calculates the thick-target bremsstrahlung distribution and x-ray attenuation due to filtering. For an incident beam energy of 19.53 MeV, a total charge of 136.8 µC, and geometry similar to Axis 1, the total dose onto a Cu foil is 489.5 rads. MCNP simulations are run with similar geometry for comparison to DOSECALCX. Both photon spectra are used to estimate the activation in different foils of a 5.067 cm2 area, and 0.1 mm thickness. These activation estimates will be used to plan experimental measurements to deduce the initial activation at exposure time from the decay curves of each element.

[1] Largent, BT, Burris-Mog, TJ, & Moir, DC. (2018). DOSECALCX, A Bremsstrahlung Radiation Dose Code for Electron Beam Targets. https://doi.org/10.2172/1485362

[2] Kulesza, JA, et al. (2022). MCNP^® Code Version 6.3.0 Theory & User Manual. https://doi.org/10.2172/1889957