Lead Oxide (PbO) for direct conversion fluoroscopic detectors

Polycrystalline Lead Oxide (PbO) is being investigated as a photoconductive materials for application as X-ray-to-charge transducer in direct conversion x-ray detectors used in fluoroscopy and radiology. Previous usage of PbO films in Plumbicon vacuum tubes for optical imaging ensures its appropriate photoconductive properties. In combination with high X-ray absorption coefficient due to high atomic number of Pb and the theoretically established conversion gain together indicates high potential for radiological medical imaging application.;Although very promising, at the current stage of development of PbO photoconductive layers thick enough for X-ray imaging applications have not yet achieved the expected conversion efficiency and not yet shown adequate temporal behavior for fluoroscopic applications: PbO suffers from image "lag" (i.e. the residual current following an x-ray pulse) and high dark current that limits the application of electric fields to below 3.5 V/im, which is a major factor preventing the attainment of high conversion efficiency.;Here we present our study on optimization of PbO technology to produce thick uniform layers capable of withstanding elevated electric fields with extremely low dark current previously achievable only in optical grade thin PbO films used in Plumbicons. Application of high electric field and low dark current allowed us to measure the electron-hole pair formation energy W+/- using the pulse height spectroscopy (PHS) method. Previous measurements of W+/- have been relatively indirect, whereas PHS is shown to be a more accurate technique. Fast temporal response for short X-ray pulses reveals high carrier mobility. Field dependency of W+/- (which is found to be higher than previously shown and to decrease as a function of electric field), dark current kinetics and X-ray response are reported. Our findings indicate that improved PbO layers are suitable for applications in direct conversion X-ray imaging detectors for a variety of applications.