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Cosmic X-Ray Experiment

NSSDC ID: 1971-083A-03
Mission Name: OSO 7
Principal Investigator: Prof. Laurence E. Peterson


The UCSD cosmic X-ray instrument was a sensitive detector mounted in the rotating wheel section of the spacecraft so that it viewed the celestial sphere in 6 months. The objectives of the experiment were (1) to locate accurately known and newly detected X-ray sources, (2) to measure the intensity of the sources, and (3) to analyze the spectrum of the sources over the range of 7 to 500 keV. The experiment capabilities were (1) a full conical look angle of 6.5 deg, (2) a spatial resolution of plus/minus 0.2 deg, (3) a sensitivity of 5.E-4 photons/(sq cm-s), (4) an energy resolution provided by the use of 126 channels for the 7-500 keV range, and (5) a maximum detection rate of 3.12 photons/s. The X-ray detector was a 4-in diameter by 3/8-in thick NaI(Tl) scintillation crystal viewed by a 3-in. photomultiplier tube (PMT). The detector was surrounded by a thick CsI(Na) scintillation crystal shield with 10 holes bored through it along the optical axis to define the field of view of the detector. The shield scintillator was viewed by six PM tubes. Light pulses in the NaI crystal caused by X-rays that had passed through the holes in the shield had relatively slow rise times and had intensities proportional to the energy of the photons. The corresponding proportional current pulses out of the PM were recognized as valid events and processed by the data system. X-rays or particles that passed through the CsI shield caused light pulses with fast rise times and corresponding pulses in the shield PM tubes. Pulses from the shield PM tubes were used to electronically reject simultaneous pulses from the detector PM. In this way X-rays passed through the collimating holes were processed as useful data. For more information, see M. P. Ulmer et al., Ap. J., v. 178, p. L61, 1972.


  • Astronomy: Gamma Ray
  • Astronomy: X-Ray

Additional Information

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



NameRoleOriginal AffiliationE-mail
Prof. Laurence E. PetersonPrincipal InvestigatorUniversity of California, San
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