Physics News Update, Number 488

Number 488, June 9, 2000, 2000 by Phillip F. Schewe and Ben Stein

METALLIC DEUTERIUM. Livermore physicists have the best evidence yet that deuterium, a heavy form of hydrogen, is metallic at pressures as low as 50 GPa with temperatures near 8000 K. These conditions are near those expected in Jupiter's interior. The experiment in question uses the powerful Nova laser to push a plunger which in turn sets up a shock wave and high pressures in a sample of liquid deuterium. At pressures as low as 20 GPa the deuterium shows both an increasing compressibility (meaning that D2 molecules are being dismembered and crushed together; see figure at Physics News Graphics) and increasing reflectance (one sign of metallic behavior is that the sample reflects rather than absorbs or transmits light) with rising pressure.

The transition from insulator to metal is continuous and at any one time the liquid may be a mixture of D atoms, D ions plus electrons free to roam, and even a few D dimers (2-atom molecules), trimers, tetramers, etc. Previous work with metallic hydrogen suggested that the Jupiter's metallic core was larger than originally thought. This new work (Peter Celliers, 925-424-4531), with deuterium hints further that because of the continuous metalization transition there may be no distinct boundary inside Jupiter between the metal core and the outer molecular envelope. (Celliers et al., Physical Review Letters, 12 June 2000; Select Article.)

ISOTOPES DON'T HAVE TO BE RADIOACTIVE to be used as tracers in clinical medicine and environmental studies. At next week's meeting of the APS Division of Atomic, Molecular, and Optical Physics, Daniel Murnick of Rutgers University (973-353-5446, murnick@newark.rutgers.edu) will describe how advances in optical spectroscopy are making stable isotopes a cost-effective and useful medical tool. For example, they have led to a fast, less expensive (and FDA-approved) breath test for gastrointestinal infections created by Helicobacter pylori, a bacterium which can cause duodenal ulcers and other disorders.

In the test, a patient swallows a small dose of the organic compound urea, labeled with the isotope carbon-13. If the bacteria is present, they will break down the urea into ammonia and carbon dioxide containing C-13. Shortly thereafter, technicians collect the patient's exhaled breath, which has both C-13 and the more common isotope C-12. The breath samples enter a small cell containing a pair of electrodes. With electric current flowing between the electrodes, the breath is illuminated with an "isotope laser," a light source tuned to an energy transition in a specific isotope. By the "optogalvanic effect," the proper isotope will respond to the light and enter a different energy state, thereby changing the conductivity between the electrodes.

By monitoring the changes in current while alternately exciting C-13 and C-12 with different isotope lasers, the researchers can detect abnormally high C-13/C-12 ratios indicating the presence of H. pylori bacteria. Murnick will explain how this technique can also potentially be used for real-time monitoring of atmospheric CO2, present in concentrations 300 times less than that of a human breath. (Talk C2-1; meeting program.

JUPITER'S MOON IO BEARS WATCHING. The most volcanically active object in the solar system, Io has recently been visited again (in Feb 2000) by the Galileo spacecraft, and the surface shows noticeable changes from a flyby made in Oct 1999. Results reported at last week's American Geophysical Union meeting in Washington, DC include the following: John Spencer of the Lowell Observatory summarized infrared observations of Loki, Io's (and the solar system's) greatest volcano, whose immense lava flow, the size of Connecticut, is unequaled on Earth in historic times. In the past few months the flow has warmed by 40 K and greatly grown.

Rosaly Lopes-Gautier of JPL showed several new hot spots (potential volcanos) discovered with a high-resolution infrared spectrometer. One might extrapolate from the density of sources, she said, that Io might have more than 300 volcanos, representing a colossal energy loss.

Meanwhile, Alfred McEwen of the University of Arizona described the Chaac canyon which, with a depth of 2.8 km and an average steepness of 70 degrees, is much more dramatic than the Grand Canyon in Arizona (1.5 km deep and 30 degrees in steepness). See also Science, 19 May 2000.