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New tracer better explains bone metabolism
Livermore researcher Darren Hillegonds and retired Laboratory scientist John Vogel of Livermore’s Center for Accelerator Mass Spectrometry, with scientists from Belgium, Germany, and Switzerland, have successfully demonstrated that bone calcium can be labeled with the long-lived radioisotope calcium-41. In addition, they found that urinary calcium-41 excretion can be followed over periods of years using accelerator mass spectroscopy (AMS), the most sensitive technique for isotopic analysis at the ultratrace level. The research findings were published in the October 11, 2006, online version of Analytical and Bioanalytical Chemistry. The paper won the journal’s Best Paper Award for 2006.
This new technique could be used in preventing and treating age-related osteoporosis, which has become a major public health concern because the mean life expectancy has increased three years per decade over the last century—a trend that seems set to continue. A more detailed understanding of calcium metabolism in bone would help to better define the diet and lifestyle strategies needed for osteoporosis prevention. At present, no methodologies allow direct measurement of small changes in bone metabolism with high sensitivity and on a short-term scale. These changes accumulate with time and may play a significant role in maintaining bone health.
For AMS calcium detection, bones are labeled with calcium-41, and bone metabolism is tracked by observing how much of the tracer is lost through urine over time. According to Hillegonds, even a small amount of tracer can sensitively monitor key aspects of bone health over a lifetime.
Contact: Darren Hillegonds (925) 424-2413 (hillegonds1@llnl.gov).

Interatomic potential energy surface of bismuth mapped
Laboratory researcher Art Nelson and an international team of physicists have mapped the interatomic potential of crystallized bismuth when it approaches a solid–solid phase transition. The findings were a result of work performed at the Sub-Picosecond Pulse Source at the Stanford Linear Accelerator Center and appeared in the February 2, 2007, issue of Science.
Nelson’s research experiments, which are supported by Livermore’s Laboratory Directed Research and Development Program, are the first to combine the use of a high-brightness linear accelerator-based x-ray source with pulse-by-pulse timing reconstruction for femtosecond resolution. This approach allows for the first quantitative characterization of the interatomic potential energy surface of a highly excited solid. Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible. At high excitation densities, the interatomic forces that bind solids and determine many of their properties can be significantly altered.
The availability of bright sources of ultrafast hard x rays, such as future free-electron lasers, opens the possibility to follow atomic motion with the spatial and temporal resolution required to study the fastest atomic vibrations and the making and breaking of chemical bonds.
Contact: Art Nelson (925) 422-6488 (nelson63@llnl.gov).

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UCRL-52000-07-4 | April 10, 2007