The x‐ray sensitivity of amorphous selenium for mammography

A study of the x‐ray sensitivity of amorphous selenium (a‐Se) for digital mammography has been performed. A uniform layer of a‐Se was deposited on a glass substrate with electrodes on both surfaces. The deposition procedure was identical to that used for a‐Se flat‐panel detectors. A high voltage was applied to the top surface of the a‐Se layer in order to establish an electric field Then the sample was exposed to x rays with 27 kVp spectra generated from an x‐ray tube with a molybdenum (Mo) target. The mean x‐ray energy of the spectrum used was ∼16.6 keV. The x‐ray current generated by the a‐Se layer was measured as a function of From the current measurement and the estimation of total x‐ray energy absorbed in the a‐Se, the energy required to create one electron‐hole pair (EHP), W , was determined as a function of It was found that at the most commonly used of 10 V/μm, W was measured as 64 eV. This is considerably higher than the widely accepted typical value of measured at higher x‐ray photon energies (e.g., 50 keV). The dependence of W as a function of can be best fitted using the empirical expression of This relationship is consistent with the results obtained at higher x‐ray energies. This article provides an accurate measurement of x‐ray sensitivity of a‐Se at mammographic energies independent of detector operation, such as the most recently developed flat‐panel detectors. The results will be a useful tool for investigation and optimization of a‐Se‐based x‐ray imaging detectors, such as determination of pixel fill‐factor and optimal during operation.