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Cosmic-Ray Gradient

NSSDCA ID: 1968-100A-06

Mission Name: Pioneer 9
Principal Investigator:Prof. William R. Webber


This experiment utilized a telescope comprised of five solid-state sensors, a Cerenkov detector, and an anticoincidence shield. The telescope axis was perpendicular to the spacecraft spin axis. As determined by two coincidence modes and electronic discrimination of sensor output pulses, particles measured were (1) electrons in three contiguous energy intervals between 0.31 and 5.1 MeV, (2) protons in five contiguous energy intervals between 2.2 and 42 MeV, and (3) alpha particles in contiguous energy intervals between 5.8 and 42 MeV/nucleon. A third coincidence mode measured the sum of counts due to electrons above 0.6 MeV and nuclei above 14 MeV/nucleon. A fourth coincidence mode measured the sum of nuclei above 42 MeV/nucleon and electrons above 5.1 MeV. Spacecraft spin-integrated directional fluxes were measured in the various modes. Accumulation times and readout intervals were dependent on the telemetry bit rate and were typically in tens of seconds. In all cases, they were longer than the spacecraft spin period.

Alternate Names

  • Pioneer9/Cosmic-RayGradient

Funding Agency

  • Unknown (United States)


  • 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
Prof. William R. WebberPrincipal InvestigatorUniversity of New
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