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Charged Particle (Iowa)

NSSDCA ID: 1961-032A-04

Mission Name: Ranger 2
Principal Investigator:Prof. James A. Van Allen


The medium-energy-range particle detector experiment comprised a suite of charged particle detecting modules designed to measure the characteristics of protons and electrons in the energy region from a few keV to a few MeV (covering the range from interplanetary plasma particles to cosmic rays). Two different detector types were used: four cadmium sulfide detectors and two Geiger counters.

The four cadmium-sulfide detectors are arranged in two pairs pointing in different directions, both about 45 degrees from the Sun. The detectors are approximately 2-mm square and between 0.1 and 0.3 mm thick. One of the detectors has a "magnetic broom", a small magnet that deflects electrons with energies less than 500 keV. The other three have no magnets. The detectors are cadmium-sulfide crystals in which the conductivity is proportional to the rate of deposition of enegy of ionization, so that for a constant voltage across the crystal, the current flow can be related to the energy flux. The detection range for the three detectors without the magnet is greater than 100 eV for protons and electrons. The detector with the magnet detects protons greater than 400 eV and electrons over 500 keV. One of the detectors without the magnet has a shutter that restricts the angular resolution to 0.001 to 0.005 steradians, the other three have an angular resolution of 0.01 steradians.

The Geiger Counter is an Anton 213 end-window type detector. It has an effective counting area of approximately 0.12 square cm and incorporates a 1.2 mg per square cm mica window, which allows measurement of protons greater than 500 keV and electrons greater than 35 keV. The dynamic range of the detector is over 500,000 counts per second.

The other Geiger counter was an Anton 112 cylindrical counter with a 30 mg per square cm titanium wall capable of measuring protons greater tha 3 MeV and electrons greater than 200 keV, with a cone angle resolution of 10 degrees. The effective counting area is (parallel - perpendicular to axis) 3 - 13 square cm.

Alternate Names

  • Ranger2/MediumEnergyParticleDetectors

Facts in Brief

Power (avg): 0.2 W


  • Space Physics: Heliospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Prof. James A. Van AllenPrincipal InvestigatorUniversity of Iowa
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