Analysis of returned lunar samples by techniques based on Mössbauer spectrometry

Abstract

Some years ago the suggestion was made that and the use of this technique permits the acquisition of Mossbauer effect measurements could usefully be analytic data without altering the chemical composition applied to the study of lunar and planetary surface of the sample. This is an important consideration in materials (HERZENBERG and TOMS, 1966). During the working with irreplaceable lunar samples. The techpast months this application has started to take place nique is especially appropriate for studying solid and with the first studies of returned lunar samples. solid powder samples of materials such as the lunar The Mossbauer effect and its application to mineral rock chips and fines. Many common and important studies have been discussed at previous NATO Advanminerals, both terrestrial and lunar, have an appreciable ced Study Institutes (O’REILLY, 1969; JOHNSON, 1969), iron content and ~ Mossbauer spectrometry perso this paper will include only a briefdescription of the mits one to distinguish among them in many cases technique. Mossbauer spectrometry is based on the (HERZENBERG and RILEY, 1970a, c). Since the strength resonant interaction of gamma rays with nuclei in of each characteristic mineral resonance depends upon solids. In a typical Mossbauer spectrometry experiment, the number of iron nuclei contributing to it, we can gamma radiation is directed at the sample and its evaluate the distribution of the iron through different resonant absorption spectrum is measured. The resmineral phases and also the total abundance of iron onant absorption spectrum of the sample depends on in the sample. Furthermore, Fe57 Mossbauer spectrothe nuclear hyperfine interactions of the resonating metry provides the possibility of distinguishing among nuclei which are present in the sample. These hyperfine different oxidation states of iron (JOHNSON, 1969; interactions depend upon the local molecular or crystalHERZENBERG and RILEY, 1970a, c). This has been of line environment of the resonating nuclei. Thus, the special interest in connection with the lunar samples. character of the Mossbauer spectrum of the sample We have used two general types of instruments in dependsupon the mineral phases present in it, and on these studies. Transmission spectrometers were used their relative abundances. for measuring the spectrum of resonance radiation The nuclides which are now amenable to Massbauer transmitted through a thin sample of the material, such spectrometry represent about 40 elements (GREENas a thin uniform layer of powdered rock or soil, or a WOOD et a!., 1969). Of these, by far the most useful in specially mounted thin section of a lunar rock. We geoscience applications has been iron, and only iron have also developed a scattering spectrometer for has yet been found in sufficient abundance in lunar studying large bulk specimens in their original state by samples to permit direct Mossbauer spectrometry measuring the resonantly emitted radiation backseatstudies (LSPET, 1969, 1970). Hence, all of the Mosstered from the surface of a specimen when it is exposed bauer effect studies of returned lunar material so far to the beam of resonant radiation. Wefind the scatterhave been performed by studying the resonances of the ing technique very valuable, and of possible future stable ~ nuclei which are naturally present in the interest in connection with the development of a MOsslunar material. bauer spectrometer for remote analysis of planetary MOssbauer spectrometry is basically nondestructive, surfaces.