APS News

Atom Laser, CEBAF Results Mark 1997 Spring Meeting

mgmprizeApproximately 1,500 physicists assembled in Washington, DC, for the 1997 Joint Spring Meeting of the APS and the American Association of Physics Teachers (AAPT), 18-21 April. 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 experimental results from the Thomas Jefferson National Accelerator Facility, formerly CEBAF (see page 2); the first detailed energy spectrum of an active galaxy nucleus (see page 4), and the world's first atom laser, using a Bose-Einstein condensate as its center (see page4). General interest sessions included such topics as the biological effects of low-dose radiation, the future of science and technology in North America (see page 4), trends in federal support of science education, and highlights of the 100-year anniversary of the discovery of the electron. In addition, the AAPT organized several sessions devoted to issues in education, some in conjunction with APS committees or units, including a Monday morning session devoted to national science education standards, co-sponsored with the APS Forum on Education (FED).

Another prominent feature was a special plenary session on Sunday afternoon. The session was led off by a stirring memorial of C.S. Wu by colleague T.D. Lee. This was followed by an address by APS Past President Robert Schrieffer of the National High Magnetic Field Lab in Florida, reviewing the many ways in which high-temperature superconductivity is more complicated than its colder counterpart. Michael Turner of the University of Chicago and Fermilab addressed what he calls the two most pressing issues in cosmology today: the nature of dark matter and the origin of the tiny inhomogeneities (perhaps starting out as tiny quantum disruptions or fluctuations) that would later grow into the galaxy clusters observed in the present universe. Finally, Mark Spano of the Naval Surface Warfare Center discussed progress in understanding, and even controlling, chaos. These studies have already been usefully applied to actual physical systems such as lasers, chemical reactions, combustion engines, hearts, and brain tissue.

On the Wednesday evening prior to the start of the meeting, the APS organized an exhibit and reception featuring recent applications of fundamental physics. Scientists from laboratories around the nation presented information on global positioning, medical instrumentation and optical communications, as well as such future technologies as laser tweezers, Bose condensates, scanning tunneling microscopy, and nanotechnologies.

The traditional ceremonial banquet for the bestowal of prizes and awards was held Saturday evening, preceded by a reception hosted by APS President D. Allan Bromley (Yale University). Fourteen APS prizes and awards were presented, and the recipients gave lectures on their respective award-winning topics at various sessions throughout the week. Citations and brief biographies of the recipients appeared in the April 1997 issue of APS News.

Technical Sessions

Search for Neutrino Oscillations
Two years ago at this meeting a group of physicists from Los Alamos presented evidence for neutrino oscillation, the transformation of neutrinos from one type to another, in an experiment in which a beam of neutrinos strikes a target. The Los Alamos team, represented by William Louis, and the collaboration at the Super-Kamiokande neutrino detector, represented by Kenneth K. Young of the University of Washington, recently concluded major new data analyses. Kamiokande also searches for neutrinos from the sun, from distant supernovas, and from the decay of protons. Based on the first 100 days of research in Japan, Young reported that there are hints that not only does the neutrino have mass and can change its form ("flavor"), but it may also be more abundant at night than during the day, and more plentiful during certain times of the year. If the neutrino is found to have mass, it could constitute part of the dark matter that is believed to comprise as much as 90% of the universe.

Anti-Hydrogen Atoms
David Christian of Fermilab reported on an experiment in which anti-hydrogen atoms are produced when a gas jet is passed through an antiproton beam. Anti-atoms are produced at a rate of about one atom a day when the machine is on. Although these atoms (like those produced at the CERN lab in Geneva) have not been captured, a plan has been formulated at Fermilab for both increasing the production rate and for passing newly-made anti-H's through a strong magnet which will help to differentiate different excited-state species. At a later session, Walter Oelert of the Julich Institute of Nuclear Physics, a participant in the CERN experiment, reported on further analysis of his data and discussed the future of anti-hydrogen research at CERN, which recently announced that it will build a new facility, the Antiproton Decelerator, partly for this purpose.

Proton-Neutron Correlations
It is a little-known fact that all nuclei are superconductors, with protons that pair up with other protons and neutrons that form pairs with other neutrons. In nuclei with equal numbers of neutrons and protons, physicists believe that neutron-proton pairs can form to create a new kind of superconductivity. According to Stuart Pittel, who spoke at a Saturday morning session, these superconducting effects are believed to influence the mass of nuclei such as Chromium-48 or Tin-100 (with equal numbers of protons and neutrons) and affect the rate at which proton-neutron pairs flow between nuclei which are close together. The proton-neutron correlations are also expected to be important for single- and double-beta decays, radioactive processes in which a nucleus emits electrons or positrons along with neutrinos.

Black Hole Formation
Matthew Choptuik of the University of Texas, whose computer simulations of "naked singularities" (essentially the gravitational centers of black holes without their event horizons) obliged Stephen Hawking to pay off a famous bet, discussed critical phenomena in black hole formation at a Saturday morning session. Specifically, his detailed studies of various models of classical gravitational collapse revealed strong-field solutions which dominate the collapse dynamics at the threshold of the black hole formation, which exhibit such phenomena as universality and scaling. Other speakers at the session discussed such issues as whether black hole entropy arises from boundary states, horizon fluctuations, and quantum mass gap at the threshold of black hole formation.

Search for Life on Mars
At a Friday evening session, Jack Farmer of the NASA Ames Research Center reviewed the aims of present and future efforts to search for life on Mars. He believes that robotic field science will play a fundamental role in advancing current understanding of the planet's history. In particular, capable rovers are needed to survey a broad array of Martian rock types for in situ mineralogy and chemistry as a basis for interpreting remote sensing data obtained from orbit. "In situ mineralogical analysis will be crucial for selecting the best materials for sample return," he said, adding that rovers will need to be equipped with a suite of instruments capable of identifying acqueously-deposited sediments, as well as the capability to access rock interiors and cache small subsamples. There are still compelling reasons to mount human missions to Mars, however. While a deep subsurface hydrosphere is believed to be the most likely haven for living organisms, such exploration will require drilling to depths of tens to hundreds of kilometers. Robotic platforms are likely to provide very limited subsurface access to depths of only a few tens of meters; hence, deep subsurface drilling will most likely require a human presence.

Gamma Rays from a Free Electron Laser
Physicists at Duke University scatter ultraviolet photons from 500-MeV electrons inside a free electron laser facility to produce much higher energy (12 MeV) gamma-ray photons. By collimating the gamma flux, one can achieve a nearly mono-energetic beam. At a Saturday morning session, Eric Schreiberl reported that the emittance (the divergence) of the beam is so low that even after collimation the intensity of the gamma beam is 1000 times greater than that produced with conventional laser systems. A beam like this will be useful for cancer therapy and for high-precision gamma-ray transmission radiography. It can also be used to produce positrons and to perform sensitive studies of the atomic nucleus.

Developing a New Cryogenic Temperature Scale
In the past few years, more and more physicists have gotten closer and closer to absolute zero, with the proliferation of experiments in such fields as laser cooling, Bose-Einstein condensation, and atom lasers. The International Temperature Scale of 1990 (ITS-90) allows laboratories around the world to match their measurements to an internationally accepted scale. However, this temperature scale does not go below temperatures of 3 Kelvins, because there was not enough data in these low-temperature regions at the time ITS-90 was developed. On Saturday afternoon, researchers reported on the development of what some may consider a holy-grail for defining temperature in this region: the melting curve of helium-3, a liquid which solidifies at different temperatures depending on the amounts of pressure that are applied to it.

Low-Temperature Glow Discharge Plasmas
Low-temperature plasmas have gained prominence in recent years in rapidly developing high technology areas, such as the etching of microstructures which form the basis of computer chips and other devices; the deposition of thin films used as high-tech coatings; the clean-up of volatile organic compounds; and more generally, the controlled modification of surfaces. Most commonly used for processing purposes is low-temperature glow discharge plasmas, which are usually sustainable only below atmospheric pressure because of instabilities such as the glow-to-arc transition, which creates a high-current, spatially confined arc between the two electrodes of a plasma device, making them inefficient for technological applications.

However, at a Friday morning session, researchers at the Stevens Institute of Technology in Hoboken, New Jersey, reported on a new method for suppressing the glow-to-arc transition in dc and rf glow discharges, thus extending their operating range to atmospheric pressures. While there have been previous reports of stable glow discharges at atmospheric pressures, the Stevens method has several advantages over other approaches, including active versus passive stabilization, low energy consumption, simple engineering design, and easy scaling to larger plasma volumes. The new method will allow the efficient use of flow discharges for large-scale processing purposes without the need for costly vacuum equipment. It is already being used at Stevens to generate large volume atmospheric pressure plasma, and for the remediation of gaseous pollutants from waste streams. Other potential applications include novel lighting devices and discharge-enhanced combustion.

Chemical Sensor Design
On Monday morning, Steve Semanchik of NIST's Chemical Science and Technology Laboratory reported on recent major advances in gas sensing with the use of micromachined structures called "microhotplates," which he describes as "platforms for thin sensing films of oxide materials decorated with ultrathin islands of catalytic metals." In addition to enabling kinetic selectivity, arrays of multiple microhotplates with different active overlayers can be used to obtain the varied adsorption/ desorption/reaction characteristics needed for gas multicomponent analyses.

At the same session, A.J. Ricco of Sandia National Laboratories reported on efforts to detect volatile organic compounds using a six-device array of 97-MHz, ST-quartz-based SAW delay lines in combination with chemically sensitive interfaces, including self-assembled monolayers, plasma processed films, dendrimer-based films, and conventional polymers. His group has also applied chemical sensor array technology to investigate the surprising reactivity of Martian soil reported by Viking Lander experiments. Specifically, an instrument using an array of fiber optic micromirror-based chemical sensors was designed and built, using an array of chemically sensitive thin films, including metals, organometallics, and organic dyes to produce a pattern of reflectivity changes characteristic of the species interacting with these sensing layers.

General Interest Sessions

Biological Effects of Low-Dose Radiation
On Monday morning, the Forum on Physics and Society (FPS) organized a session presenting diverse views on the biological effects of ionizing radiation at low doses. According to session chair John Cameron (University of Wisconsin-Madison), current national and international radiation protection policy is based on the assumption of a "linear no-threshold" (LNT) model relating a population's frequency of cancer and heritable ill-health to radiation dose. The LNT model specifically predicts that any increase in dose produces an increase in probability of cancer. Speakers included Dr. Arthur Upton (New York University), chair of the NAS/NRC committee that produced a 1990 report supporting the wide use of the LNT model; Ludwig Feinendegen (Brookhaven National Laboratory) and Myron Pollycove (University of California, San Francisco), who offered contradicting evidence to the LNT model; and Daniel Strom (Pacific Northwest National Laboratory), who addressed the use and abuse of models in radiation risk management.

Trends in Federal Support of Science Education
The FPS and FED co-sponsored a Friday morning session reviewing recent trends in federal support for K-12 and undergraduate math and science education. Current initiatives include opportunities for science teachers to participate in research internships or related programs at federal and university research laboratories. Agencies covered in the session included the NSF, NASA, the Department of Energy, the National Oceanic and Atmospheric Agency, and the Department of Defense research agencies. According to Richard Stephens, a science education consultant, cross-agency initiatives in math and science education present the potential for new K-12 and undergraduate science initiatives developing from the recently enacted National Oceanic Partnership legislation administered by the Office of Naval Research, which involves nine federal research agencies. At the same session, Tom Weimer, staff director of the Subcommittee on Basic Research for the House of Representatives' Committee on Science, reported that the subcommittee is planning a comprehensive review of K-12, undergraduate, graduate, and post-graduate federal science education programs, in light of the FY 98 agency authorization bills reviewed this spring.

National Science Education Standards
At a joint AAPT/FED session on Monday morning, Bruce Alberts, president of the National Academy of Sciences, urged that the wider community of scientists help to implement the comprehensive program of science teaching standards promulgated a year ago by the National Research Council. "For the first time in our history we have a coherent national vision of where we want to go in science and math education, but the changes called for in the [standards] will be difficult to implement and take more than a decade to build," he said. "Science must become the fourth R in every school year, starting in kindergarten, not the dry memorization of science terms, but an exciting and empowering experience in problem-solving that takes advantage of the curiosity in children and increases each student's understanding of the world." Other session speakers discussed the implications of the new standards, such as its likely effect on teaching at the K-12 level.

Forum Session Award Lectures
Physicists do more than research. As administrators and citizens they are often involved with governmental and social issues of national and international importance. At a special Saturday afternoon session, the FPS recognized the work of Martin Gardner, essayist and a longtime editor at Scientific American, with the APS Forum Award. Accepting on Gardner's behalf was James Randi, a notable debunker of pseudo-scientific claims. The APS Leo Szilard Award Lecture was presented by Thomas Neff of MIT, who reported on the dangers posed by the still-potent nuclear stockpiles of the US and Russia. The APS Nicholson Medal Lecture, on the subject of scientists and totalitarian societies, was given by Li-Zhi Fang, a former dissident in China and now a professor at the University of Arizona. Manuel Cardona from Max-Planck-Institut Fr Festk"perforschung gave the APS Wheatley Award lecture on physics in Latin America

1997 Spring Meeting Program Committee

Chair: Virginia Brown, National Science Foundation

Vice-Chair: Paul Grannis, SUNY-Stony Brook

AAPT Program Chair: Thomas L. O'Kuma, Lee College
APS Program Committee: John Ahearne, Sigma Xi (FPS); Beverly Berger, Oakland University (GTG); Bunny Clark, Ohio State University (DNP); L. Craig Davis, Ford Research Laboratory (FIAP); Gordon W.F. Drake, University of Windsor (DAMOP); Nathaniel Fisch, Princeton University (DPP); James Friar, Los Alamos National Laboratory (FBSM); Howard Georgi, Harvard University (DPF); Daniel Heinzen, University of Texas-Austin (FCTG); William Herrmannsfeldt, Stanford Linear Accelerator Center (DPB); Wendell T. Hill, III, University of Maryland (COM); Rush Holt, Princeton Plasma Physics Laboratory (FED); Paul Houston, Cornell University (DLS); Marvin Kalos, Cornell University (DCOMP); Richard Lingenfelter, University of California-San Diego (DAP); Laurie McNeil, University of North Carolina (CSWP); Roberto Merlin, University of Michigan (FIP); John Rigden, American Institute of Physics (FHP); Robert Soulen, Jr., Naval Research Laboratory (IMSTG); John Weiner, University of Maryland (DCP).

Canadian Association of Physicists: Eric C. Svensson, AECL/Chalk River Laboratories (CAP vice president); See L. Chin, Universite Laval (DAMOP); David A. Clarke, Saint Mary's University (DAP); Janis McKenna, University of British Columbia (DPF); Ann C. McMillan, Atmospheric Environment Service (CSWP, DCOMP, FIP, FPS); Louis J. Dube, Universite Laval (DAMOP); Rene Roy, Universite Laval (DNP); Roberto D. Connor, University of Manitoba (FHP).

Sociedad Mexicana de Fisica: Jose L. Moran-Lopez, UNAM (1994-96 SMF president); Silvia Torres, UNAM (DAP); Juan C. D'Olivo, UNAM (DPF); Carmen Cisneros, UNAM (1996-98 SMF President, DAMOP); Maria-Ester Brandan, UNAM (DNP); Miguel A. Perez, Centro de Investigation y Estudios Avanzado (FIP).

APS encourages the redistribution of the materials included in this newspaper provided that attribution to the source is noted and the materials are not truncated or changed.

Editor: Barrett H. Ripin