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New techniques for carbon 14 dating and trace element analysis, as well as the application of nuclear particle detectors in the biomedical arena, were among the highlights presented at the annual meeting of the APS Division of Nuclear Physics, held October 30 through November 1 in Tucson, Arizona. The technical program also featured several talks on subjects related to last year's National Research Council report, "Connecting Quarks to the Cosmos," along with presentations on the nuclear physics of supernovae.
Revolutionizing Carbon Dating.
A public lecture on Wednesday evening and an invited talk on Thursday afternoon both focused on applications for accelerator mass spectroscopy (AMS), most of which center on its use for carbon 14 dating. According to Walter Kutschera (University of Vienna, Austria), AMS has revolutionized the field by measuring carbon 14 through isotope ratios rather than the classical method of beta counting, increasing the sensitivity almost one million times, which in turn enables researchers to reduce the sample size to milligram amounts, compared with several grams required for beta counting. He illustrated this point with the case of Iceman Oetzi, a well preserved 5200-year-old body found in the central European Alps in 1991.
At a special public lecture, Douglas Donahue (University of Arizona) described his team's studies of artistic artifacts, the populating of the Americas, and the study of Martian meteorites using an AMS instrument. He incorporated a small tandem electrostatic accelerator as one component of a conventional mass spectrometer, giving the ions to be analyzed kinetic energies of millions of electron volts instead of the more typical thousands of electron volts. This enabled him to use nuclear physics techniques to eliminate sources of background noise, and thus detect trace elements in concentrations of a few parts per thousand trillion.
The NRC report "Connecting Quarks to the Cosmos" outlined eleven critical scientific questions for the 21st century. Among them was determining new states of matter at exceedingly high density and temperature. This question is related to the central mission of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, according to W.A. Zajc (Columbia University), who described efforts to recreate in the laboratory states of matter similar to those that existed in the first few microseconds after the Big Bang. He summarized the project's successes to date, with particular attention given to the possibility of connecting this physics to that of the early universe.
Another important question is determining how the heavy elements from iron to uranium were made, part of the broader challenge of understanding the chemical history of the universe, according to Bradley Sherrill (Michigan State University). While a few light elements were created in the first few minutes after the Big Bang, most others were created in the subsequent 14 billion years by nuclear reactions in stellar objects. Sherrill provided an overview of the role of unstable nuclei in the cosmos and the scientific frontiers that can be addressed as scientists come to better understand their properties, and described how scientists measure and model the chemical evolution of the universe.
Kevin Lesko (Lawrence Berkeley National Laboratory) pointed out that of the 11 major scientific challenges outlined in the NRC report, about one half either require deep underground facilities to conduct the research, or said research would be significantly enhanced with such facilities. In fact, a Deep Underground Facility was one of seven recommendations included in the report, and is also a high priority for the Nuclear Physics Long Range Plan. He reviewed the scientific case for a deep underground laboratory, and progress to date in developing one.
ATTA on the Nile.
A team of scientists at Argonne National Laboratory is developing an Atom Trap Trace Analysis (ATTA) method for the analysis of two long-lived rare krypton isotopes, making it an ideal method for determining the ages of old ice and groundwater in a range beyond the reach of radio carbon dating. In ATTA, individual atoms of the desired isotope are selectively captured in a laser trap and detected by observing their fluorescence. Zheng-Tian Lu and his colleagues have used the method to date ancient ground-water of the Nubian Aquifier in the Western Desert of Egypt, one of the largest aquifiers in the world. The technique can also be used to analyze krypton 18, a fission product of uranium and plutonium, which can help verify compliance with the Nuclear Non-Proliferation Treaty.
Dual Use Detection.
The Detector Group at the Thomas Jefferson National Accelerator Facility focuses on the development and use of nuclear particle detection utilizing gas detectors, scintillation and light guide techniques. While its main function is to provide nuclear particle detector support to the lab, the group has since 1996 applied these and other technologies to the development of novel high resolution gamma ray imaging systems for biomedical applications and x-ray imaging techniques. These include systems for breast cancer detection, brain cancer therapy, and small animal imaging to support biomedical research, according to Jefferson Lab's Andrew Weisenberger.
Nuclear Physics of Supernovae.
Because Supernova type II explosions are powerful sources of neutrinos, the detection of neutrinos from a galactic supernova would provide vital information for understanding the explosion, as well as neutrino properties such as their masses and mixing angles. Cristina Volpe of the Institut de Physique Nucl?aire in Orsay, France, described how one can determine the initial neutrino spectra, and once the neutrino fluxes are known, can use supernova neutrinos to obtain limits on the less known neutrino mixing angle. Doing so requires a precise knowledge of neutrino-nucleus interaction cross sections, of equal importance for nucleosynthesis studies, and Volpe believes that building a facility for low energy neutrinos would offer the opportunity to perform systematic studies of these interactions.
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