NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

Electron and Proton Detectors

NSSDC ID: 1966-058A-05
Mission Name: Explorer 33
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 (Geiger tubes only, between 2 and 12A) and of solar, galactic, and magnetospheric charged particles. The Geiger-Mueller tubes measured electrons of energies greater than 45 to 50 keV and protons of energies greater than 730 to 830 keV. The SSD output was discriminated at four thresholds: (1) PN1, which detected protons between .31 and 10 MeV and alphas between .59 and 225 MeV, (2) PN2, which detected protons between .50 and 4 MeV and alphas between .78 and 98 MeV, (3) PN3, which detected protons between .82 and 1.9 MeV and alphas between 1.13 and 46 MeV, and (4) PN4, which detected alphas between 2.1 and 17 MeV. GM1 and the SSD were oriented parallel to the spin axis, and GM3 was oriented antiparallel to the spin axis. Data from GM1 and PN1 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 from the sun, respectively). Data were read out in either 82-s or 164-s intervals. High temperatures adversely affected the SSD particle data during the periods from September 16 to January 14 and from March 16 to July 14 of each year following September 16, 1966. However, the alpha particle data are believed to be unaffected. On rare occasions (less than 10), a GM tube would produce a high, spurious count rate for a period of several hours. This effect apparently was produced only during periods of extremely high particle and X-ray fluxes. Accumulator failures occurred on July 21, 1967, and September 24, 1967. For further details, see Van Allen and Ness, J. Geophys. Res., v. 72, p. 935, 1967.

Alternate Names

  • Electrons, Protons and X-Rays

Facts in Brief

Bit rate (avg): 0.0285 bps

Funding Agency

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


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

Additional Information

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



NameRoleOriginal AffiliationE-mail
Prof. James A. Van AllenPrincipal InvestigatorUniversity of Iowa 
[] NASA Logo -