Like oxygen, sulfur isotopes show up in different fractions in different solar system sources. Tracing their possible origins, the recent study of sulfur isotopes at beamline 9.0.2 began by flowing hydrogen sulfide gas the most abundant sulfur-bearing gas in the early solar system into a pressurized reaction chamber, where the synchrotron beam decomposed the gas and deposited elemental sulfur on "jackets" made of ultraclean aluminum foil.
The experiment was performed at four different VUV wavelengths, and the carefully stored aluminum jackets were taken to the Thiemens lab in San Diego, where Chakraborty and Jackson chemically extracted the sulfur and then measured its isotopes using Isotope Ratio Mass Spectrometry. In all samples the isotope compositions were found to be mass independent.
One source of fractionation in nature was photodissociation of hydrogen sulfide as the gas condensed to iron sulfide in the inner solar system, driven by intense 121.6-nanometer-wavelength ultraviolet light as the young star repeatedly shook with violent flares and upheavals. Different classes of meteorites and different parts of the same meteorites, such as their crust or various inclusions subsequently evolved different isotope ratios, depending on where and when in the solar system they formed. Sulfur compositions evolved independently from the way oxygen isotope compositions evolved.
The most recent target of research by the Thiemens group at beamline 9.0.2 is nitrogen, the seventh most abundant element in the solar system. On Earth, 99.63 of nitrogen is nitrogen-14, and nitrogen-15 is the remaining 0.37 percent. Measurements of the solar wind, carbonaceous meteorites, and other sources show wide swings in their proportions. The work is ongoing.
Says Musa Ahmed, "Tracking down how isotopic ratios may have evolved, we basically send thes
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory