Highlights from Indianapolis: Trapped Francium, Energy Alternatives, Age of the Universe, Gender Gap
Approximately 1,400 physicists assembled in Indianapolis, Indiana, for the 1996 Joint Meeting of The American Physical Society (APS) and the American Association of Physics Teachers (AAPT), 2-5 May. The most varied of APS meetings because of the number of APS divisions represented in the program, the Spring Meeting explored current topics in particle physics, astrophysics, fluids, particle beams, physics of beams, nuclear physics, applications, and atomic, molecular and optical physics.
Topics of technical sessions included the first entrapment of a francium atom (see story below), new data on globular clusters (see page 4), the discovery of over 100 new isotopes, (see page 3), and recent advances in nuclear-based medical imaging (see page 2). General interest sessions included such topics as the future of renewable energy sources (see page 7), gender bias in the GREs (see page 3), and the future of physics. In addition, the AAPT organized several sessions devoted to issues in education, some in conjunction with APS committees or units.
Another prominent feature was a special plenary session on Friday afternoon, modeled on the Unity Day symposia held in recent years at the annual Joint APS/AAPT Meeting. The session featured the retiring presidential address by APS Past President C. Kumar N. Patel, as well as general lectures on black holes and Bose-Einstein condensation, respectively, by Kip Thorne (California Institute of Technology), recipient of the 1996 Lilienfeld Prize, and Carl Wieman (University of Colorado/JILA) (see page 5).
The traditional ceremonial banquet for the bestowal of prizes and awards was held Saturday evening, preceded by a reception hosted by APS President J. Robert Schrieffer (Florida State University). Twelve prizes and awards were presented, and the recipients gave lectures on their respective topics at various sessions throughout the week. Citations and brief biographies of the recipients appeared in the April 1996 issue of APS News.
Neutrino Oscillations. Los Alamos scientists have found additional evidence that neutrinos have mass, observing 22 events that are consistent with muon antineutrinos oscillating into electron antineutrinos, compared to the nine events observed last year. Last year, an experiment at LANL turned up tentative evidence of neutrino oscillation, a phenomenon in which one type of neutrino (muon, electron, or tau neutrino) transforms into another. According to LANL's Fred Federspiel, the observation of the new data cannot be attributed to either known background processes or to statistical fluctuations, since the total estimated background from cosmic rays and other neutrinoes is only about four or five events. The team is also analyzing data on neutrinos produced by pions and muons decaying in flight, which have higher energies, and expects to continue collecting data with their detector over the next two years.
Record High Laser Intensity. The advent of tabletop terawatt lasers has prompted the study of new nonlinear optical effects. Donald Umstadter of the University of Michigan reported on an experiment in which a self-focusing laser beam passing through a plasma reached an intensity of 1020 W/cm2, the highest yet reported for any laser. In the process of excluding plasma electrons from a narrow region forming a thin channel through the plasma, the laser creates pressures exceeding one giga-bar, higher than any other man made pressure. The collimated and intense laser beams will eventually be used in attempts to accelerate electrons to GeV energies over a space of centimeters. A new generation of ultrashort duration high-energy electron and photon courses may thus be built, potentially the equivalent of a Stanford Linear Accelerator or Advanced Proton Source on a tabletop.
Crystalline Beams. In a Thursday morning session on advances in beams and accelerators, Jeffrey Hangst of Aarhus University in Denmark reported on efforts to cool the relative motion of particles in a circulating beam, as well as the use of resonant laser light as a diagnostic tool for studying fundamental issues in beam dynamics. According to Hangst, the great strength and speed of the laser cooling process have led scientists to believe it could be used to produce a crystalline beam, in which the ions' relative kinetic energy decreases to the point that an ordered state is formed. He summarized recent experimental progress in this area, as well as current theoretical understanding of the conditions under which a spatially ordered ion beam might be obtained.
Delta-Enhanced Multifragmentation. Scientists at Indiana University have obtained the first direct evidence for the expansion of nuclear matter using proton and helium beams from particle accelerators to heat atomic nuclei to several billion degrees. The fragments produced in the process were then analyzed with the Indiana Silicon Sphere Detector, an array consisting of 162 "telescopes" for identifying nuclear fragments formed in the disintegration of hot nuclei. The Indiana researchers concluded that the nucleus expands as much as 50 percent of its normal size before breaking apart, which corresponds to a density about one-third of normal nuclear matter. The results are relevant not only to the understanding of microscopic nuclei, but also to cosmological problems, such as supernovae and the formation of neutron stars, pulsars, or possibly black holes.
Superdeformed Nuclei. When two nuclei collide off-center, they can fuse to create a superdeformed nucleus: a football-shaped nucleus with a large amount of spin, according to scientists at Lawrence Berkeley Laboratory. Using the GAMMASPHERE detector at LBL, Teng Lek Khoo of Argonne National Laboratory and his colleagues have measured, for the first time, the total energy and angular momentum released when a superdeformed mercury-194 nucleus decays to a well-understood, lower-energy nuclear state. According to Khoo, connecting these two states paves the way toward understanding the many mysteries associated with this nuclear state.
Supersymmetry. Supersymmetry is a theory that seeks to unite quantum mechanics with general relativity. An important ingredient is the existence of certain hypothetical particles. According to the theory, each known fermion - such as an electron and quarks with a half integral spin - would have a new boson counterpart. Likewise, all known bosons - particles such as photons with integral spin - would have new fermion counterparts. Gordon Kane of the University of Michigan discussed how supersymmetry theory could be put to the test, and how certain events recorded in scattering experiments at Fermilab may already provide the first hints of supersymmetry at work.
Materials at Intense Pressures. Scientists at Los Alamos are probing the limits of experimental physics on extreme states of matter using magnetic flux compression, a technique for converting the chemical energy released by high explosives into intense electrical pulses and intensely concentrated magnetic energy. The pulse generators reach magnetic fields in excess of 1000 Tesla. Using the technique, the researchers have made discoveries about several properties of materials observed at the atomic level, including the quantum Hall effect, Faraday rotation and magnetic-field induced superconductivity. These experiments may provide answers to questions in astrophysics and planetary physics, such as clues to the state of matter inside the great gas giant planets, as well as new directions in materials science and solid state physics. Researchers will next attempt to compress argon up to 8 million atmospheres to observe the rising stages of conductivity in the gas, possibly leading to the production of metallic argon, a phase state never before seen on Earth. Until recently, the technique has been used primarily for nuclear weapons research.
Forecasting Individual Storms. Present weather models used in National Weather Service Operations employ a grid resolution of 45-60 kilometers, which is sufficient to forecast larger-scale features, such as fronts and low-pressure systems, but not enough to anticipate isolated storms over specific counties or cities. Kelvin Droegemeier of the University of Oklahoma has developed a new computational model that provides storm forecasts up to six hours in advance, with up to one-km resolution. This may lead to enabling forecasters to predict individual storms, which can be around five km in size.
Unlike present weather models the new model takes into account vertical accelerations, which are generally not negligible for storms, where the vertical wind velocity can be as strong as the horizontal wind velocity. The system was tested over the Southern Great Plains last year and will be run again this year during collaborative testing with American Airlines over their major hubs in Dallas and Chicago. The tests will help determine whether this model can be used to reduce the number of needlessly re-routed plane flights.
Colliding Beam Fusion. Conventional nuclear fusion reactions are initiated by magnetically confining a deuterium and tritium plasma and introducing energy sources to generate the high-temperature conditions necessary for fusion. Norman Rostoker of the University of California-Irvine proposed that researchers should consider conducting experiments that explore the possibility of using exclusively high-energy particles to create fusion.
Experiments have shown that when a small amount of high-energy particles are trapped in a magnetic field, they are confined for long periods of time. With longer confinement times, fusion is easier to achieve. According to Rostoker, this approach could open the possibility of fusing hydrogen with isotopes such as boron-11. It would produce charged-particle by-products that are have advantages over the neutrons that result from the traditionally used deuterium-tritium fuels.
New Measurements of G. Conflicting measurements of Newton's constant G, which relates the gravitational force between two objects to their mass and separation, were presented at the 1995 APS/AAPT Spring Meeting (see APS News, July 1995); the highest discrepancy was more than half a percent greater than the accepted CODATA value. The results have stimulated a number of new measurements of G by various groups worldwide. For example, a group at Wuppertal University in Germany is improving their ability to measure their source mass position, and plans to move their apparatus to another site where temperature and noise level control will be better. Also underway are measurement experiments at Zurich University, University of California, Irvine, the University of Washington, and JILA in Boulder, Colorado, as well as in Russia, Taiwan and Japan.
Accelerators in Industry. Phil Womble of Oak Ridge National Laboratory described a technique for detecting "remote-handled transuranic waste," which are neutron-emitting radioactive by-products, heavier than uranium, and a significant component of nuclear waste produced at Argonne National Laboratory and elsewhere. In the new technique, a compact accelerator generates a tiny amount of fission in the waste, creating by-products that help identify isotopes in the sample. In the same session, George Vourvopoulos of Western Kentucky University discussed how neutrons produced by compact accelerators can be used to perform real-time analysis of coal to help testing and blending of different types of coal. The technique can also be used to burn coal economically and environmentally safety, as well as to test coal by-products, such as ash.
Effects on Radiation at Low Doses. In 1928, the International Commission on Radiological Protection advised that for prudent public protection, no amount of radiation should be accepted without expectation of benefit, based on 1924 studies by physicist Jeffrey Crowther that showed linearity at low doses. However, this cautious approach is based on direct epidemiological data obtained from studies at high radiation doses, since a large number of test subjects would be needed to find a small effect low doses, with considerable bioassay effects. In a Sunday morning session, Bernard Cohen of the University of Pittsburgh reviewed two possible approaches to study the linear-no threshold theory (LNT) of radiation carcinogenesis in the low dose region.
The best approach, according to Cohen, is use of the radon vs. lung cancer relationship, but these studies have not been sufficiently robust to extrapolate meaningful conclusions from the data. An alternative is to study lung cancer rates for various counties and compare them to average radon exposure in those counties. Cohen has found that regardless of corrections for smoking prevalence, the mortality rate actually decreased with increasing radiation doses, in sharp contrast to predictions, with a standard deviation factor of 20. This discrepancy lead to the conclusion that the LNT theory may well fail in the low dose region.
Science, Politics and Human Rights. Where does one draw the line between scientific activity and complicity with a totalitarian regime? Nicholson Medal recipient Yuri Orlov of Cornell University examined the ethical decisions a scientist must face when confronted by political realities that make the pursuit of science morally challenging and/or professionally difficult. In 1986, Orlov was stripped of USSR citizenship and deported to the U.S., where he has continued to be active in the human rights arena while doing physics research at Cornell. He discussed the implications associated with speaking out, and extended the moral dilemma to U.S. scientists who must decide whether or not to collaborate with colleagues who hold positions of high power in repressive regimes.
Special thanks to Philip F. Schewe and Benjamin P. Stein of the American Institute of Physics Office of Public Information for contributing to the coverage of technical sessions in this issue.
1996 JOINT MEETING PROGRAM COMMITTEE:
Chair: David Cassell, Cornell University; Vice-Chair: Virginia Brown, Lawrence Livermore Laboratory; AAPT Program Chair: Ronald Edge, University of South Carolina; APS: Judy Franz,; Program Committee: Beverly Berger, Oakland University (GTG); Fred Dylla, CEBAF (FIAP); Robert Erdman, Keithley Instruments, Inc. (IMSTG); Charles Falco, University of Arizona (FIP); Richard Freeman, AT&T Bell Laboratories (DAMOP); Joan Frye, Howard University (COM); Katherine Gebbie, NIST (CSWP); Edward Gerjuoy, University of Pittsburgh (FPS); Paul Grannis, SUNY-Stony Brook (DPF); Geoffrey Greene, NIST (PCMTG); Franz Gross, College of William & Mary (FBSTG); Beverly Hartline, CEBAF (FED); Wick Haxton, University of Washington, (DAP); Richard Hazeltine, University of Texas (DPP); Barry Klein, University of California-Davis (DCOMP); Claudio Pelegrini, University of California-Los Angeles (DPB); Lee L. Riedinger, University of Tennessee (DNP); John Rigden, American Institute of Physics (FHP); and Steven Sibener, University of Chicago (DCP).
Meeting arrangements were made by Michael Scanlan and Tammany Buckwalter of the APS Meetings Department.