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Low-Energy Proton and Alpha Detector

NSSDCA ID: 1967-051A-09

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


This experiment used a dE/dx versus 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 two 4.48-s intervals every 2.73 min. The relative contributions to the 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, which was performed simultaneously on the output of the solid-state detectors eight times every 2.73 min. 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 1.1 to about 4 MeV. Data from any one level were transmitted once every 2.73 min. The anticoincidence scintillator failed in March 1968. This resulted in somewhat higher background count rates, which rendered isotopic (but not charge) separation more difficult. Except as already noted, the experiment performed well from launch until May 3, 1969 (spacecraft reentry date).

Alternate Names

  • IMP-F/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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