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Charged Particles

NSSDCA ID: 1961-020A-03

Mission Name: Explorer 12
Principal Investigator:Prof. James A. Van Allen


The experiment was designed to measure the flux and energy spectrum of charged particles and cosmic rays and to determine their spatial and temporal distribution over the spacecraft orbit. The detectors included (1) a shielded Anton type 302 omnidirectional Geiger-Mueller tube, which detected protons with E>23 MeV and electrons with E>1.6 MeV, (2) an electron magnetic spectrometer utilizing three thin-windowed Anton type 213 directional Geiger-Mueller tubes sensitive to electrons with energies from 40 to 100 keV, and (3) three directional cadmium sulfide crystals for measurements of the total flux of protons with energies from 1 keV to 10 MeV and electrons with energies from 200 eV to 500 keV. All directional detectors were mounted so that the axes of their fields of view were perpendicular to the satellite spin axis. (The initial spin period was 2.2 s.) Counts in each detector were accumulated for 10.24 s, and the contents of the accumulators were telemetered at the end of each sampling interval. The encoder accumulators were time shared so that each detector response was sampled once every 79 s. The experiment operated satisfactorily from launch until spacecraft failure on December 6, 1961. For further details, see Frank, L. A., J. Geophys. Res., v. 71, p. 4631, 1966.

Alternate Names

  • A Study of Trapped Radiation, Solar Particle Radiation, and Cosmic Rays
  • Explorer12/ChargedParticles


  • Space Physics: Magnetospheric Studies

Additional Information

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



NameRoleOriginal AffiliationE-mail
Prof. Louis A. FrankOther InvestigatorUniversity of
Dr. Brian J. O'BrienOther InvestigatorDepartment of Environmental
Dr. John W. FreemanOther InvestigatorRice University
Mr. C. D. LaughlinOther InvestigatorMcDonald Observatory
Prof. James A. Van AllenPrincipal InvestigatorUniversity of Iowa
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