A Unique Radiation Detection Concept for a Miniature Particle Spectrometer

A three-channel particle spectrometer employing charge multiplying semiconductor detectors and tunnel diode discriminators has been constructed, environmentally tested and calibrated to detect low energy protons. The three channels have been calibrated to detect protons > 0.5 MeV, >1.5 MeV, and >45 MeV. The instrument is five orders of magnitude more sensitive to protons than to electrons above 500 KeV which ensures successful operation in the midst of electrons injected into the earth´s radiation belt from the starfish experiment. The unique features of this instrument are: (1) Discriminates uniquely against a low energy photon background. (2) Electrical noise immunity due to the integration of the detector to the discriminator to give a high signal level output to the binary counter. (3) Thermally generated noise does not compete with the detected signal at the discriminator. The miniature instrument is a result of simple detection circuitry and the use of microelectronic elements in the data compressor. The data compressor consists of three binary counters having a storage capability of 218-1 bits. Each counter has a thin film network to octally encode the binary counts into an analog voltage. The counters have a 1 MHz count rate. This paper describes the instrument design and its characteristics which reflect the design constraints of the flight vehicle. The calibration of the instrument for a small half-angle cone of low energy protons from a Van De Graaff accelerator is discussed.