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Scientists reported the latest results on experiments exploring the quark–gluon plasma at Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) at the 2005 fall meeting of the APS Division of Nuclear Physics (DNP), held in conjunction with the Japanese Physical Society (JPS), September 18-22, on the island of Maui in Hawaii. Other technical highlights included research into unstable nuclei and supernova core collapse, homeland security screening applications, semiconductor failure analysis, and setting priorities for the future of nuclear physics.
It was second joint meeting between the DNP and the JPS, both of them organized in the hopes that such conferences would serve as a meeting ground to engender cooperation and the exchange of ideas among nuclear scientists from the US and Japan, as well as from other Pacific Rim countries. The first joint meeting, held in 2001, was a resounding success, with more than 800 participants in attendance. The 2005 meeting was even more successful, with more than 900 attendees, a third of them from Japan.
Saturday, September 17th, featured a special “Physics Fun Day” at the Queen Ka’ahumanu Shopping Center as part of the year-long World Year of Physics celebration. There were hands-on science activities for adults and children of all ages, as well as a Physics Olympics targeting middle and high school students, and a resource table for physics teachers. In addition, Lawrence Krauss, a professor at Case Western Reserve University and author of the bestselling The Physics of Star Trek, gave a free public lecture at the Maui Arts and Cultural Center on “Einstein’s Biggest Blunder: A Cosmic Mystery.”
Mind Your QGPs. Last year, Brookhaven scientists made the surprising announcement that they had observed evidence of the strongly-coupled quark-gluon plasma (QGP) in nucleus-nucleus collisions at RHIC, although its exact nature isn’t quite what physicists expected: it appears to be a quark-gluon liquid. Several scientists presented results from the most recent experiments seeking to characterize the bulk properties and dynamical evolution of this unique phase of matter, among them Duke University’s Steffan Bass. RIKEN’s Yasuyuki Akiba reviewed the latest measurements of heavy quarks (charm and beauty) at RHIC, which should shed even more light on the QGP’s properties.
RIKEN Upgrades. At the RIKEN facility in Japan, beams of unstable nuclei (called radioactive isotope, or RI, beams) have been used to uncover many new nuclear properties and insights into nuclear structure. RIKEN’s Tohru Motobayashi summarized achievements to date and outlined plans for a new project, the RI Beam Factory (RIBF) at RIKEN, which is now under construction and expected to come online in 2006. RIBF will provide a much wider range of RI beams with higher intensities than the present facility.
Collapsing Supernovae. The RI beams at the RIKEN facility have also been used to study nuclear burning processes involving unstable nuclei, which appear to play a critical role in the explosion mechanism of core-collapse supernovae–and hence in the nucleosynthesis of all the heavy elements in the cosmos. Kohsuke Sumiyoshi of Japan’s National Astronomical Observatory has found that the nuclear reactions of neutron-rich nuclei play crucial roles in some nucleosynthesis processes.
Gail McLaughlin of North Carolina State University followed Sumiyoshi. While astrophysicists have understood the mechanism for producing the heaviest elements for half a century, “the astrophysical site remains a mystery,” she said. Possibilities include the neutrino-driven wind of Type II supernovae and the outflow from accretion disks surrounding black holes. Such disks tend to form when neutron stars merge, or when rapidly rotating massive stars collapse. Both scenarios result in a significant flux of neutrinos, which can then impact the neutron-to-proton ratio and thus the process of nucleosynthesis.
Helping Secure the Homeland. Scientists at Lawrence Livermore National Laboratory are developing a new system to reduce the likelihood of false negative and false positive detections of fissile material in ship cargo. Approximately 6 million cargo containers arrive at US seaports annually, carrying up to 30 tons of non-homogenous cargo on each one, according to LLNL’s Jennifer Church. It is extremely difficult to detect highly enriched uranium and other nuclear material concealed within such containers using existing monitors, partly because of extreme attenuation of low energy gamma rays in the cargo. The new technique uses a neutron beam to induce fission, combining it with a wall of plastic scintillators to detect delayed high energy gamma rays after beta decay of the fission
Meanwhile, in Japan, researchers have used the detection system of near-horizontal cosmic-ray muon radiography equipment–originally developed for probing volcanic mountains–to probe the inner structure of a blast furnace. They measured the thickness of the brickwork to glean critical information to predict the lifetime of the furnace. Future work will focus on extending the muon radiography method to detect selected elements of concealed nuclear materials using a compact accelerator system.
Neutrons’ Failing Grades. Neutron-induced failures in semiconductor devices are of increasing concern to the industry. Neutron interactions in semiconductor devices produce ionized recoils or reaction products, thereby depositing charge and causing various common failures, according to S.A. Wender of the Los Alamos Neutron Science Center (LANSCE). Predicting the failure rate depends on knowing the neutron flux in the environment of a particular device, as well as how various devices respond to neutrons.