By studying the origins of different isotope ratios among the elements that make up today's smorgasbord of planets, moons, comets, asteroids, and interplanetary ice and dust, Mark Thiemens and his colleagues hope to learn how our solar system evolved. Thiemens, Dean of the Division of Physical Sciences at the University of California, San Diego, has worked on this problem for over three decades.
In recent years his team has found the Chemical Dynamics Beamline of the Advanced Light Source (ALS) at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) to be an invaluable tool for examining how photochemistry determines the basic ingredients in the solar system recipe.
"Mark and his colleagues Subrata Chakraborty and Teresa Jackson wanted to know if photochemistry could explain some of the differences in isotope ratios between Earth and what's found in meteorites and interplanetary dust particles," says Musahid (Musa) Ahmed of Berkeley Lab's Chemical Sciences Division, a scientist at the Chemical Dynamics Beamline who works with the UC San Diego team. "They needed a source of ultraviolet light powerful enough to dissociate gas molecules like carbon monoxide, hydrogen sulfide, and nitrogen. That's us: our beamline basically provides information about gas-phase photodynamics."
Beamline 9.0.2, the Chemical Dynamics Beamline, generates intense beams of VUV vacuum ultraviolet light in the 40 to 165-nanometer wavelength range (a nanometer is a billionth of a meter) which can be precisely tuned to mimic radiation from the protosun when the solar system was forming.
Oxygen and sulfur are the third and tenth most abundant elements in the solar system and two of the most important for life. Their isotopic differences from Earth's are clearly seen in many different kinds of meteorites. Thiemens's team first used beamline 9.0.2 in 2008 to test a theory, called "self-shielding," about why oxygen-16 is
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory