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Phoswich-Cerenkov Counter Telescope

NSSDCA ID: 1961-013A-01

Mission Name: S 15
Principal Investigator:Prof. William L. Kraushaar


This experiment was designed to search for high-energy gamma rays (greater than 50 MeV) from the celestial sphere. The basic detector scheme consisted of a sandwich of NaI and CsI scintillating crystals (20 g/sq cm), viewed by a single photomultiplier, and a Lucite Cerenkov counter, viewed by two photmultipliers. It was completely surrounded by a shield of scintillating plastic viewed by five photomultipliers. The sandwich detector provided high-atomic-number material for the pair production process, i.e., energetic gamma rays were converted into electron-positron pairs. The electrons and positrons then entered the Cerenkov counter, which detected particles traversing its volume in only the downward sense. The simultaneous electric signals from its two PMTs indicated that one or more charged particles had traversed the telescope. The signals or lack of signals from the surrounding plastic shield at the instant the telescope had been triggered indicated whether the triggering was caused by an uncharged or charged particle. Also, the "last" and "total" components of the signals from the photomultiplier that viewed the sandwich detector afforded a method of distinguishing neutron and gamma-ray induced events. The experiment performed normally from launch until November 17, 1961. For more information, see W. Kraushaar et al., Ap. J., v. 141, p. 845, 1965.

Alternate Names

  • Gamma-Ray Telescope Experiment
  • S15/Phoswich-CerenkovCounterTelescope

Funding Agency

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


  • Astronomy: Gamma Ray

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. George W. ClarkOther InvestigatorMassachusetts Institute of
Prof. William L. KraushaarPrincipal InvestigatorUniversity of Wisconsin-Madison
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