Photomultiplier tube gain stabilization for radiation dosimetry system
First Claim
1. A method for measuring the electron multiplication gain of a photo-detector utilizing a light source, the method comprisingmeasuring light from said light source by said photo-detector using photon counting and current integration measurement modes to obtain both a photon count and a current integral, andcalculating said electron multiplication gain as a ratio of said current integral to said photon count.
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Abstract
Methods and means for measuring and adjusting the gain of a photomultiplier tube (PMT), or other photo-detector with electron multiplication gain, for the purpose of achieving accurate light measurement, such as in a luminescent radiation dosimeter reader. With a PMT illuminated by a light emitting diode or other light source, the PMT output signal is measured in two modes, signal integration and photon pulse counting. The measured PMT gain is calculated as the ratio of the integrated signal to the photon pulse count. The PMT high voltage may be adjusted to cause the measured PMT gain to correspond to an established calibration gain value, or the data from the PMT may be adjusted to compensate the deviation of the measured PMT gain from the calibration gain value. The light source may be a controllable light source that can be adjusted to provide a specific photon count rate output as measured by the PMT. This invention provides for maintaining light measurement calibration without requiring temperature stabilization or a fixed light source.
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Citations
15 Claims
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1. A method for measuring the electron multiplication gain of a photo-detector utilizing a light source, the method comprising
measuring light from said light source by said photo-detector using photon counting and current integration measurement modes to obtain both a photon count and a current integral, and calculating said electron multiplication gain as a ratio of said current integral to said photon count.
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6. A method for adjusting the electron multiplication gain of a photo-detector to maintain said photo-detector operation at a calibration gain value utilizing a light source, the method comprising
measuring light from said light source by said photo-detector using photon counting and current integration measurement modes to obtain both a photon count and a current integral, and adjusting said electron multiplication gain to obtain a ratio of said current integral to said photon count that corresponds to said calibration gain value.
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11. Electronic circuit means for determining the electron multiplication gain of a photomultiplier tube as a ratio of integrated current to photon counts, wherein said electronic circuit means both counts incident photons and integrates output current from said photomultiplier tube under illumination from a light source, said electronic circuit means including
a high frequency transimpedance amplifier that converts said output current to a voltage in a manner that preserves output pulses resulting from said incident photons, a comparator and a pulse counter which determine said photon counts by counting said output pulses, circuits that integrate said voltage to determine said integrated current, and a high-voltage power supply for operation of said photomultiplier tube.
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14. A device for reading luminescent phosphors which utilizes a photomultiplier tube to measure light emission from said luminescent phosphors and a light source for calibration of electron multiplier gain of said photomultiplier tube, wherein
light from said light source incident on said photomultiplier tube is measured using photon counting and current integration measurement modes to obtain both a photon count and a current integral, and said electron multiplication gain is set to a calibration value by adjusting high voltage to said photomultiplier tube so that a ratio of said current integral to said photon count corresponds to said calibration value.
Specification