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 muA maximum average cathode current. The laser produces 3x10(7) photons at 650 nm per approximately 100 ps pulse, with up to 10(7) 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 1x10(6) and 3x10(6) 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.