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Low-Energy Proton and Alpha Detector

NSSDCA ID: 1969-053A-09

Mission Name: IMP-G
Principal Investigator:Dr. Frank B. McDonald


This experiment used a dE/dx vs E telescope with one thin and two thick surface-barrier, solid-state detectors and an anticoincidence plastic scintillator counter. The two thick detectors acted together as one detector. The telescope axis was perpendicular to the spacecraft spin axis. Counts of particles penetrating the thin detector and stopping in a thick detector were accumulated for a 4.48-s interval once each 2.73 min for each of two counting modes (counting modes are defined with respect to the energy deposited in the thin dE/dx detector). Good separation of protons and alpha particles was achieved by this mode distinction. The relative contribution to each count rate of protons and alpha particles with energies between 4.2 and 19.1 MeV/nucleon and energy spectral information were determined by 1024-channel pulse-height analysis performed simultaneously on the output of the solid-state detectors four times every 2.73 min for each of the two threshold modes. Protons stopping in the thin detector (and particles penetrating it) were measured by passing the output signal through an eight-level energy threshold discriminator. The eight corresponding proton energies ran from 0.6 to about 4 MeV. Data from any one level were transmitted once every 2.73 min. There were also two solid-state detectors that looked along the spacecraft spin axis and that were identical except for differences in the covering foil thicknesses. Both detectors responded to electrons in the 80-to 200-keV range. One responded to protons between 83 keV and 2 MeV and the other to protons between 200 keV and 2 MeV. Spectral information was gathered by subjecting the output signals from each detector to eight-level energy threshold discrimination. Data from each of the eight levels and each of the two detectors were transmitted once each 5.46 min. Except for a 2-week period in March 1970 when the telescope data were noisy, all the detectors functioned normally.

Alternate Names

  • IMP-G/Low-EnergyProtonandAlphaDetector


  • Space Physics: Magnetospheric Studies
  • Space Physics: Heliospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. George H. LudwigOther InvestigatorNOAA Environmental Research Laboratories
Dr. Frank B. McDonaldPrincipal InvestigatorNASA Goddard Space Flight Center
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