The photo-multiplier X ray detector, consisting of a multiplier photo-tube to measure the light emitted by a fluorescent screen, has been extended in its use to the measurement of alpha-, beta-, and gamma-rays, high energy electrons and protons, and neutrons. Improved light-gathering methods and high frequency circuits have resulted in registration of individual quanta of all these radiations as pulses rising above the noise level of the photo-multiplier's input-stage dark current of 105
electrons per second, permitting use of a discriminator-counter circuit. This removes the sensitivity limitation inherent when the instrument is used only for current measurement. At high intensities the detector can be switched from pulse counting to current measurement, with a wide range of overlap for calibration. Employing commercial photo-tubes and screens, this detector is simple, rugged, compact, and spectacularly fast. It competes favorably in sensitivity with all other detectors, including
the Geiger counter, and it can cover a tremendous range of intensities. It is most suitable for use with narrow beams of radiation. The thin-window technique is unnecessary for beta-rays, since the phosphor is exposed. Dr. Kuan-Han Sun is responsible for extending the detector to neutron measurement, using boron impregnated phosphors to convert neutrons to alpha-particles.
Invention of scintillation counters.