Kinetic Boltzmann approach adapted for modeling highly ionized matter created by x-ray irradiation of a solid

We report on the kinetic Boltzmann approach adapted for simulations of highly ionized matter created from a solid by its x-ray irradiation. X rays can excite inner-shell electrons, which leads to the creation of deeply lying core holes. Their relaxation, especially in heavier elements, can take complicated paths, leading to a large number of active configurations. Their number can be so large that solving the set of respective evolution equations becomes computationally inefficient and another modeling approach should be used instead. To circumvent this complexity, the commonly used continuum models employ a superconfiguration scheme. Here, we propose an alternative approach which still uses “true” atomic configurations but limits their number by restricting the sample relaxation to the predominant relaxation paths. We test its reliability, performing respective calculations for a bulk material consisting of light atoms and comparing the results with a full calculation including all relaxation paths. Prospective application for heavy elements is discussed.

Figure 1

All electronic configurations (27 boxes) and all possible direct photoinduced transitions (74 lines) for x-ray irradiated atomic carbon. Solid lines correspond to photoionization processes and dashed lines to Auger decays. The 19 transitions included in scheme (i) are depicted in red. Blue lines represents the additional 7 transitions added to scheme (ii), which yields 26 transitions in total.

Figure 2

Average charge and average energy absorbed per atom within carbon bulk irradiated with a Gaussian pulse of (a),(b) soft x rays ($E_{\mathrm{photon}}=1000$ eV, $I_{max}={10}^{16}\mathrm{W}/{\mathrm{cm}}^2$) and (c),(d) hard x rays ($E_{\mathrm{photon}}=5000$ eV, $I_{max}={10}^{18}\mathrm{W}/{\mathrm{cm}}^2$). Pulse maximum was at $20\mathrm{fs}$. Only photoionization and Auger processes were considered.

Figure 3

Average charge and average energy absorbed per atom within carbon bulk irradiated with a Gaussian pulse of (a),(b) soft x rays ($E_{\mathrm{photon}}=1000\mathrm{eV}, I_{max}={10}^{16}\mathrm{W}/{\mathrm{cm}}^2$) and (c),(d) hard x rays ($E_{\mathrm{photon}}=5000$ eV, $I_{max}={10}^{18}\mathrm{W}/{\mathrm{cm}}^2$). Pulse maximum was at 20 fs. Collisional processes were included.