Characterization of a pulsed X-ray source for fluorescent lifetime measurements

To search for new, fast, inorganic scintillators, we have developed a bench-top pulsed X-ray source for determining fluorescent lifetimes and wavelengths of compounds in crystal or powdered form. This source uses a light-excited X-ray tube which produces X-rays when light from a laser diode strikes its photocathode. The X-ray tube has a tungsten anode, a beryllium exit window, a 30 kV maximum tube bias, and a 50 μA maximum average cathode current. The laser produces 3×10⁷ photons at 650 nm per ~100 ps pulse, with up to 10⁷ pulses/sec. The time spread for the laser diode, X-ray tube, and a microchannel plate photomultiplier tube is less than 120 ps fwhm. The mean X-ray energy at tube biases of 20, 25, and 30 kV is 9.4, 10.3, and 11.1 keV, respectively. We measured 140, 230, and 330 X-ray photons per laser diode pulse per steradian, at tube biases of 20, 25, and 30 kV, respectively. Background X-rays due to dark current occur at a rate of 1×10⁶ and 3×10⁶ photons/sec/steradian at biases of 25 and 30 kV, respectively. Data characterizing the X-ray output with an aluminum filter in the X-ray beam are also presented