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X-ray Fluorescence Spectrometer

NSSDCA ID: 1966-078A-03

Mission Name: Luna 11
Principal Investigator:Dr. S. L. Mandel'shtam


The X-ray fluorescence spectrometer was designed to measure soft X-rays emitted from the surface of the Moon due to the fluorescence of elements excited by impinging solar X-radiation. The instrument was an RFL-F type X-ray spectrometer comprised four Geiger counters and an optical sensor, all mounted on the side of the spacecraft.

Counters 1 and 2 were used as radiation receivers with 10-micron thick aluminum windows with an area of 3 cubic cm. They could measure soft X-rays in the 8 - 14 angstrom wavelength range. The field of vision was 0.8 steradian, the geometric factor for the registration of isotropic radiation was 12.6 square cm. The counters were filled with a mixture of neon, xenon, and oxygen. They were sensitive to lines of aluminum and magnesium. Counter 3 was identical but had an additional gold-silver filter to view cosmic rays and electrons with energies above 50 keV. These 3 counters were nadir-pointing towards the lunar surface when the spacecraft was in the proper orientation with the engine end down. Counter 4 had a small (0.05 square cm) aluminum window, was pointed towards the Sun, and was used to measure solar x-radiation at wavelengths from 8-14 angstroms.

An optical sensor was used to ensure the counters were facing the Moon and Sun as appropriate, it was a silicon phototransformer with a low sensitivity output for sensing the Sun and a higher sensitivity output for the Moon. The counter readings were registered by logarithmic intensimeters and scaling circuits, and transmitted to Earth with the optical sensor readings. The counters were all covered with a 1 mm thick aluminum cover for the first readings, the cover was then removed by ground command.

Alternate Names

  • Luna11/XrayFluorescenceSpectrometer

Funding Agency

  • Russian Space Agency (U.S.S.R)


  • 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. S. L. Mandel'shtamPrincipal InvestigatorRussian Academy of Sciences
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