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X-Ray Fluorescence Spectrometer (XRFS)

NSSDCA ID: 1975-075C-13

Mission Name: Viking 1 Lander
Principal Investigator:Dr. Priestley Toulmin, III


This experiment utilized an energy-dispersive X-ray fluorescence spectrometer (XRFS) in which four sealed, gas-filled proportional counters detected X rays emitted from samples of Martian surface materials irradiated by X rays from radioisotope sources (iron-55 and cadmium-109). The output of the proportional counters was subjected to pulse-height analysis by an onboard step-scanning, single-channel analyzer with adjustable counting periods. This instrument was located inside the lander body, and samples were delivered to it by the lander surface sampler. Calibration standards were an integral part of the instrument. Reconstructed spectra yielded surface composition data with accuracies ranging from a few tens of parts per million for trace elements to a few percent for major elements.

Alternate Names

  • Inorganic Analysis
  • Viking1Lander/XRFS
  • XRFS

Facts in Brief

Mass: 1.95 kg
Power (avg): 3.5 W

Funding Agency

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


  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Priestley Toulmin, IIITeam LeaderUS Geological Survey
Dr. Benton C. ClarkTeam MemberMartin-Marietta
Dr. Alexander K. BairdTeam MemberPomona College
Dr. Klaus KeilTeam MemberUniversity of New
Dr. Harry J. Rose, Jr.Team MemberUS Geological Survey

Selected References

  • Toulmin, P., III, et al., Inorganic chemical investigation by X-ray fluorescence analysis - The Viking Mars lander, Icarus, 20, 153-178, doi:10.1016/0019-1035(73)90048-1, 1973.
  • Clark, B. C., et al., Inorganic analyses of Martian surface samples at the Viking Landing sites, Science, 194, No. 4271, 1283-1288, doi:10.1126/science.194.4271.1283, Dec. 1976.
  • Clark, B. C., III, et al., The Viking X ray fluorescence experiment: Analytical methods and early results, J. Geophys. Res., 82, No. 28, 4577-4594, doi:10.1029/JS082i028p04577, Sept. 1977.
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