Some Applications and Properties of One- and Two-Dimensional Position-Sensitive Proportional Counters

A new method was developed for determining the position of ionizing events by measuring the risetime of output pulses from detectors having high resistance collectors. Basically, these detectors are distributed RC lines; information about the location of an ionizing event is obtained from the analysis of the frequency spectrum of the detector output pulse, and the energy loss of this event in the detector is measured by analyzing the amplitude of the same output pulse. Three typical prototype detectors were constructed and tested in a series of imaging and diffraction experiments using ionizing radiation. The spatial uncertainty for collimated 210Po alpha particles was 0.15 mm fwhm for a 200-mm-long proportional detector. The spatial uncertainty for collimated 20-kev x rays was 0.5 mm fwhm for a 400-mm-long detector. A two-dimensional system using parallel wires was developed and evaluated. With only four preamplifiers and relatively simple shaping and timing circuitry, 24,000 resolution elements (measured at fwhm) were obtained with a 30-wire counter having a sensitive area of 75 × 120 mm2. These position-sensitive detectors are well suited for application in the life sciences for the localization of radioactive tracers in medical studies or in the structure determination of large organic molecules, with x-ray or neutron diffraction; in fluorescent x-ray or neutron spectroscopy; small-angle scattering experiments with x rays or neutrons.; magnetic spectroscopy of protons and other charged particles; two-dimensional chromatography; x-ray astronomy; and fission physics experiments.