Evaluation of a linear photodiode array detector for synchrotron small-angle x-ray scattering measurements

A linear photodiode array position-sensitive detector for synchrotron small-angle x-ray scattering was constructed by coupling a fiber-optic face plate coated with a thin layer (∼40 μm) of phosphor (Y2O2S:Tb) onto an electrostatically focused, intensified photodiode array detector (EG&G, PARC, Model 1422) originally designed for visible light applications. The x-ray detector was thoroughly evaluated. It showed excellent linearity of response to the incident x-ray intensity (less than 1%), stable pixel uniformity (an average of ±5%), good spatial linearity (±1 per 100 pixels), and a net gain of ∼17 counts/x-ray photon at 8 keV. The detector quantum efficiency was about 1 for a signal-to-noise ratio of greater than ∼5%. No damage to individual pixels was found after exposure to a main beam of ∼1010 x-ray photons/mm2/s. A finite afterglow (≳5 s) was observed for the phosphor inside the intensifier tube. The afterglow that could limit fast time-resolved experiments could be significantly improved by replacing the present intensifier with one using a fast-decay phosphor. The detector usable length could be increased from the present 25 to 50 mm by replacing the fiber-optic face plate with a 2:1 taper.