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<p>Irradiation of air by X-rays, particularly during diagnostic and medical imaging procedures, induces a temporary ionization of its constituents and may lead to the formation of reactive species such as O₂<sup>+</sup>, O₂<sup>−</sup> and O₂<sup>2</sup>⁻. This study analyzes photon transport as well as scattering and backscattering phenomena in air and tissue-equivalent media, in order to evaluate dose, energy, and angular distributions. A Monte Carlo code named Irradose has been developed to simulate these processes in cylindrical geometries containing air, an HCNO phantom representing the patient, and an aqueous medium. The model was validated by comparison with the PHITS and Geant4 codes, showing good agreement with deviations below 5%. The results highlight a progressive attenuation of the beam dose in air between the source and the phantom, estimated at 1.2%. They also show a higher dose deposition in the HCNO phantom. Backscatter from this medium contributes significantly to the secondary photon field in air, with a maximum of 14.62% at 0.15&#xa0;MeV and a dominant angular distribution around 2.4&#xa0;rad. The ionic species O₂<sup>+</sup>, O₂<sup>−</sup> and O₂<sup>2–</sup> are discussed, as well as the limitations of this work and the associated perspectives.</p>

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Monte Carlo study of air ionization by X-ray photons and backscattering under diagnostic conditions using the developed Irradose code

  • 期刊论文

  • 发表日期：

    2026年7月13日

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  • Omar El Basraoui,
  • Oumayma Qassimi,
  • Chaymae Yahyaoui,
  • Lahcen El Amri,
  • Najim Tahiri,
  • Omar El Bounagui

摘要

Irradiation of air by X-rays, particularly during diagnostic and medical imaging procedures, induces a temporary ionization of its constituents and may lead to the formation of reactive species such as O₂+, O₂− and O₂2⁻. This study analyzes photon transport as well as scattering and backscattering phenomena in air and tissue-equivalent media, in order to evaluate dose, energy, and angular distributions. A Monte Carlo code named Irradose has been developed to simulate these processes in cylindrical geometries containing air, an HCNO phantom representing the patient, and an aqueous medium. The model was validated by comparison with the PHITS and Geant4 codes, showing good agreement with deviations below 5%. The results highlight a progressive attenuation of the beam dose in air between the source and the phantom, estimated at 1.2%. They also show a higher dose deposition in the HCNO phantom. Backscatter from this medium contributes significantly to the secondary photon field in air, with a maximum of 14.62% at 0.15 MeV and a dominant angular distribution around 2.4 rad. The ionic species O₂+, O₂− and O₂2– are discussed, as well as the limitations of this work and the associated perspectives.