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Proportional Counter Telescope

NSSDCA ID: 1959-004A-01

Mission Name: Explorer 6
Principal Investigator:Dr. John A. Simpson


A triple-coincidence omnidirectional proportional counter telescope was used to observe protons (with E>75 MeV) and electrons (with E>13 MeV) in the terrestrial trapped radiation region. The scientific objective of the telescopes was to determine some of the properties of high-energy radiation in interplanetary space, including the proportion of counts due to X-rays versus those due to protons and other high-energy particles. Comparison with results from the Cosmic Ray Ionization Chamber makes it possible to determine the type and energy of particles responsible for the measurement.

Each telescope consists of seven proportional counter tubes, six in a concentric ring around the seventh running parallel along their lengths. These bundles of tubes lie on their sides projecting through the top of one of the equipment boxes in the hexagonal base of Ranger 1. Three of the outer tubes are exposed to space and three project into the equipment box. Each set of three is connected electronically into a group that feeds into a pulse amplifier and pulse shaper. The central tube feeds into its own equivalent circuit.

The two telescopes were designated a "low-energy" and high-energy" telescope, differing only in the amount of shielding and its configuration. The counters in the high-energy telescope were 3-inch long, 0.5 inch diameter brass tubes with a thickness of 0.028 inches. A lead shield of 5 gm per square cm thickness surrounds the entire assembly. The low-energy unit has the same size tubes, but made of steel with a wall thickness of 20 +- 0.1 mil (0.508 +- 0.0025 mm). Half the assembly has 5 grams per square cm lead shielding along the length of the tubes. The unshielded half of the assembly is the exposed portion that particles can reach without encountering spacecraft structural material, giving an angular resolution of under 180 degrees for low-energy particles.

The low-energy telescope can detect protons with energies greater than or equal to 10 MeV and electrons greater than or equal to 0.5 MeV. The high-energy telescope detects 75 MeV and above protons and 13 MeV and above electrons in triple-coincidence, and bremsstrahlung above 200 keV in the central tube.

When a particle passes through the bundle of tubes, the electronic circuit determines which groups have been penetrated. If a pulse comes from all three groups at once, a triple-coincidence, the particle was a high-energy one, rather than a low-energy one or an X-ray. The triple-coincidence events are telemetered together with the single counts from the center tube to determine counts due to high-energy vs. low-energy sources. The high-energy telescope counting rate allows correction of the low-energy telescope data in order that the particle flux incident on the unshielded portion of the low-energy unit can be calculated. Comparing data from the low-energy telescope and the Cosmic-Ray Ionization Chamber (both detect particles in the same energy range) makes it possible to determine the average ionization per particle, from which the type and energy of the particle can be determined.

Several magnetic storms occurred during the active life of the experiment. The date of transmission of the last useful information was October 6, 1959, after which the transmitter failed to operate. NSSDC has all the useful data that now exist.

Alternate Names

  • Explorer6/ProportionalCounterTelescope

Facts in Brief

Mass: 1.8 kg
Power (avg): 0.5 W

Funding Agency

  • NASA-Office of Space Science (United States)


  • Space Physics: Magnetospheric Studies

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Charles Y. FanOther InvestigatorUniversity of Arizona
Prof. Peter MeyerOther InvestigatorUniversity of Chicago
Dr. John A. SimpsonPrincipal InvestigatorUniversity of Chicago
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