*Article* **Absolute Double-Differential Cross Sections of Ultrasoft Isochromatic X-ray Radiation in Electron Scattering on Atoms**

**Aleksei S. Kornev 1, Boris A. Zon 1, Vladislav E. Chernov 1,\*, Miron Ya. Amusia 2,†, Petr Kubelík 3 and Martin Ferus 3**


**Abstract:** We calculate double-differential cross sections of ultrasoft X-ray bremsstrahlung in electron scattering by Ar, Kr, and Xe atoms in the soft-photon approximation. The calculations are done for the isochromatic spectra (i.e., dependence on the electron energy at a fixed photon energy of 165 and 177 eV). The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (Phys. Rev. A **80**, 022707 (2009)) for the above-mentioned photon energies. For low electron energies, our theoretical isochromatic spectra are in quantitative agreemen<sup>t</sup> with the experimental data for Ar. For Kr, the agreemen<sup>t</sup> is qualitative while agreemen<sup>t</sup> with the Xe data is poor.

**Keywords:** ultrasoft X-ray bremsstrahlung; isochromatic spectra

**Citation:** Kornev, A.S.; Zon, B.A.; Chernov, V.E.; Amusia, M.Y.; Ferus, M.; Kubelík, P. Absolute Double-Differential Cross Sections of Ultrasoft Isochromatic X-ray Radiation in Electron Scattering on Atoms. *Atoms* **2022**, *10*, 86. https:// doi.org/10.3390/atoms10030086

Academic Editor: Anatoli Kheifets, Gleb Gribakin and Vadim Ivanov

Received: 11 August 2022 Accepted: 21 August 2022 Published: 24 August 2022

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