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The X-ray sensitivity is one of the most important parameters for X-ray photoconductors; it is usually described in terms of the electron-hole pair creation energy W± – the average energy required to generate a single detectable pair of electron and hole. This parameter accounts only for the detected carriers, reflecting that only a fraction of the X-ray–generated charges are collected, while the rest are lost through the recombination processes. The charge recombination results in an effective W± that is not a material parameter but rather a characteristic of the detection system, which remains larger than its theoretical value 𝑊± 0 and depends on the applied electric field F, X-ray energy E and exposure X. In this work, we characterize the X-ray sensitivity of amorphous lead oxide (a-PbO) photoconductor, which is considered as one of the most promising replacements for amorphous selenium (a-Se) for radiographic, fluoroscopic, and tomosynthesis applications, and examine the underlying mechanisms responsible for charge recombination. W± was measured in a wide range of electric fields (1–20 V/μm), X-ray exposures (0.02–2 R) and energies (29–51 keV). W± decreases with both the electric field and X-ray energy, saturating at 18–32 eV/ehp depending on the energy. W± increases with radiation exposure, especially at lower fields and higher energies. The particular dependencies of W± on these parameters, especially X-ray energy-dependent W±, conclude that the columnar recombination mechanism dominates in the a-PbO photoconductor with a secondary contribution of the bulk recombination.
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