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Electron and Proton Detectors

NSSDCA ID: 1967-070A-01

Mission Name: Explorer 35
Principal Investigator:Prof. James A. Van Allen


Three EON type 6213 Geiger-Mueller (GM) tubes (GM1, GM2, and GM3) and a silicon solid-state detector (SSD) provided measurements of solar X rays (GM1 only, between 2 and 12 A) and charged particles in the vicinity of the moon. GM1 and GM3 measured electrons of energies greater than 48 to 50 keV and protons of energy greater than 740 to 820 keV, while GM2 was shielded by a cap with approximately 1 gram per sq cm (limiting its response to protons of energies greater than about 55 MeV). The SSD output was discriminated at four thresholds: (1) PN1, which detected protons between .32 and 6.3 MeV, (2) PN2, which detected protons between .48 and 3.0 MeV, (3) PN4, which detected alphas between 2 and 10.2 MeV, and (4) PN3, which was sensitive to particles of Z greater than 3, including carbon 12 between .58 and 9.5 MeV per nucleon, nitrogen 14 between .514 and 13.9 MeV per nucleon, and oxygen 16 between .466 and 18.8 MeV per nucleon. GM1 and SSD were oriented perpendicular to the spacecraft spin axis, GM2 was oriented parallel to the spin axis, and GM3 was oriented antiparallel to the spin axis. Data from GM1, PN1, and PN4 were divided into data from quadrants oriented with respect to the sun (sectors I, II, III, and IV were centered 180, 270, 0, and 90 deg away from the sun, respectively). Data were read out every 82 or 164 s, and the experiment performance was normal. For more details, see Van Allen and Ness, J. Geophys. Res., v. 74, p. 71, 1969, but note the revised SSD energy levels.

Alternate Names

  • Explorer35/ElectronandProtonDetectors
  • GM Counter and Solid

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Solar Physics: Gamma Ray
  • Solar Physics: X-Ray
  • Planetary Science: Fields and Particles

Additional Information

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



NameRoleOriginal AffiliationE-mail
Mr. Robert L. BrechwaldGeneral ContactUniversity of
Prof. James A. Van AllenPrincipal InvestigatorUniversity of Iowa
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