P. Buford Price

(PICTURE OF PBP)

Send mail to Prof. Price.
(Click on the above image to see Prof. Price relaxing after a dip in the Antarctic ocean.)

P. Buford Price is Professor in the Graduate School at the University of California at Berkeley. He leads a group of graduate students and post-doctoral fellows whose research, while centered in the Physics Department and the Space Sciences Laboratory, is interdisciplinary in nature. During the last decade his research shifted from nuclear physics, cosmic ray astrophysics, and particle astrophysics into high-energy neutrino astrophysics, with the development of the AMANDA observatory at the South Pole and installation of the first of 80 strings that will compromise the cubic kilometer array called IceCube. He recognized quite early that in order to track high-energy muons and do neutrino astronomy, one had to develop a better understanding of the optical properties of glacial ice and to map the distribution of dust particles in the deep ice in which the AMANDA phototubes are imbedded. These studies led him and his colleagues into research in glaciology and paleoclimatology and to the invention of an optical dust logging instrument, a biospectrologger, and an ultrasonic grain-size logger. As a spinoff of AMANDA, Price developed an interest in life in extreme environments. His paper, A Habitat for Psychrophiles in Deep Antarctic Ice, stimulated several successful searches for microbial life in liquid veins in sea ice, lake ice, and glacial ice and led to two NASA grants for Mars instrument development. His group is using various imaging techniques to detect microorganisms living in veins and on small mineral particles in solid ice. In response to the anthrax attacks in fall, 2002, Price and Andrew Westphal developed a way to do rapid sizing of individual Bacillus spores, which has opened up a new area of biological study. Another of Price's activities has been writing biographies of recently deceased physicists.

The group, as of February 2005, includes

Post-doctoral researchers Kurt Woschnagg, Ryan Bay, Rodin Porrata, Dave Hardtke, and Ignacio Taboada.

Graduate students Nathan Bramall, Justin Vandenbroucke, Michelangelo D'Agostino, Andres Morey, and Robert Rohde.

Undergraduate student Camas Tung

Development technician Michael Solarz

Administrative assistant Lavern Navarro

links:

Cosmic ray astrophysics (recent papers in refereed journals):

  1. Measurement of the Isotopic Composition of Iron and Nickel in the Galactic Cosmic Rays. A. J. Westphal, V. G. Afanasyev, P. B. Price, M. Solarz, V. V. Akimov, V. G. Rodin, and N. I. Shvets,Astrophys. J. Lett. 468, 679-685 (1996).
  2. Evidence against Stellar Chromospheric Origin of Galactic Cosmic Rays. A. J. Westphal, P. B. Price, B. A. Weaver, and V. G. Afanasiev, Nature 396, 50-52 (1998).
Particle astrophysics (recent papers in refereed journals):
  1. Flux Limits for Supermassive Magnetic Monopoles that Do Not Catalyze Baryon Decay. P. B. Price, Phys. Rev. Letters 73, 1305 (1994).
  2. Limits on Dark Matter Using Ancient Mica. D. P. Snowden-Ifft and P.B. Price, Physical Review Letters, 74, 4133 (1995).
  3. Search for Weakly Interacting Massive Particles in Ancient Mica. P. B. Price and D. Snowden-Ifft, Nucl. Phys. B (Proc. Suppl.), 43, 149-151 (1995).
  4. D. Snowden-Ifft, E. S. Freeman, and P. B. Price, Reply to Comment on "Limits on Dark Matter Using Ancient Mica", in Phys. Rev. Letters 76, 331-332 (1996).
Nuclear physics (recent papers in refereed journals):
  1. Electromagnetic Production of Hyperfragments in Ultrarelativistic Heavy-Ion Collisions. Y. D. He and P. B. Price, Nuclear Physics A 585, 363c-364c (1995).
  2. Identification of the New Isotope 114Ba and Search for its Alpha and Cluster Radioactivity. A. Guglielmetti, R. Bonetti, G. Poli, P. B. Price, A. J. Westphal, Z. Janas, H. Keller, R. Kirchner, O. Klepper, A. Piechaczek, E. Roeckl, K. Schmidt, A. Plochocki, J. Szerypo and B. Blank, Physical Review C 52, 740-743 (1995).
  3. Non-observation of 12C Cluster Decay of 114Ba. A. Guglielmetti, R. Bonetti, G. Poli, R. Collatz, Z. Hu, R. Kirchner, E. Roeckl, N. Gunn, P. B. Price, B. A. Weaver, A. Westphal, and J. Szerypo, Phys. Rev. C 56, R2912-R2916 (1997).
AMANDA (Antarctic Muon and Neutrino Detector Array)
With a total of 677 downlooking phototubes in a cylindrical array of radius 100 m, AMANDA is a working neutrino observatory installed in South Pole ice at depths 1500 to 2300 m. It detects neutrinos passing upward through the entire earth. AMANDA can answer fundamental questions in astrophysics (the nature of blazars and of gamma ray bursters), cosmology (the nature of the dark matter that comprises more than 90% of the mass of the universe), cosmic ray physics (origin of the highest energy cosmic rays), and particle physics (properties of neutrinos including their oscillations and their behavior in a gravitational field). Click here for examples of muon tracks in AMANDA.

AMANDA (selected papers in refereed journals):

  1. The Search for Neutrino Sources Beyond The Sun, S. Barwick, F. Halzen, and P.B. Price, Inter. J.Mod. Phys. A 11, 3393-3413 (1996).
  2. Comparison of Optical, Radio, and Acoustical Detectors for Ultrahigh-Energy Neutrinos, P.B. Price, Astroparticle Physics 5, 43-52 (1996).
  3. The AMANDA Neutrino Telescope: Principle of Operation and First Results, E. Andres, et al., Astroparticle Physics 13, 1-20 (2000).
  4. Observation of high energy neutrinos using Cherenkov detectors embedded deep in Antarctic ice, AMANDA Collaboration, Nature 410, 441-443 (2001).
  5. Role of Group and Phase Velocity in High-Energy Neutrino Observatories, P. B. Price and K. Woschnagg, Astroparticle Physics 15, 97-100 (2001).
  6. Limits to the Muon Flux from WIMP Annihilation in the Center of the Earth with the AMANDA Neutrino Detector. J. Ahrens and the AMANDA collaboration, Phys. Rev. D 66, 032006 (2002).
  7. Search for Supernova Neutrino Bursts with the AMANDA Detector, J. Ahrens et al., Astropart. Physics 16/4, 345-359 (2002).
  8. Observation of High Energy Atmospheric Neutrinos with AMANDA, J. Ahrens et al. Phys. Rev. D 66, 012005 (2002).
  9. Search for Neutrino-Induced Cascades with the AMANDA Detector, J. Ahrens et al., Phys. Rev. D 67, 012003 (2003).
  10. Search for Point Sources of High Energy Neutrinos with AMANDA, J. Ahrens et al., Ap. J. 583, 1040-1057 (2003).
  11. Physics and Operation of the AMANDA-II High Energy Neutrino Telescope, S. W. Barwick, for the AMANDA Collaboration, astro-ph/0211269 (2002).
  12. Limits on Diffuse Fluxes of High Energy Extraterrestrial Neutrinos with the AMANDA-B10 Detector, J. Ahrens et al. (the AMANDA Collaboration), Phys. Rev. Lett. 90, 251101 (2003).
  13. Search for Extraterrestrial Point Sources of Neutrinos with AMANDA-II, T. Hauschildt and D. Steele and AMANDA Collaboration, J. Ahrens et al. (AMANDA Collaboration). Phys. Rev. Lett. 92, 071102 (2004).
  14. Flux limits on ultrahigh-energy neutrinos with AMANDA-B10. The AMANDA Collaboration. M.Ackermann et al., Astroparticle Physics 22, 339-353 (2005).
  15. Measurement of the cosmic ray composition at the knee with the SPASE-2/AMANDA-B10 detectors. AMANDA and SPASE Collaborations (J. Ahrens et al.). Astroparticle Physics 21, 565-581 (2004).
  16. Search for neutrino induced cascades with AMANDA. The AMANDA Collaboration. Astroparticle Physics 22, 127-138 (2004).
IceCube Neutrino Observatory
Congress has funded IceCube, which will be the largest detector in the world, with 80 strings each containing sixty 10-inch phototubes extending from 1450 to 2450 m depth in ice at the South Pole. The collaboration includes more than 150 scientists from universities and research institutes in the U.S., Europe, and Asia. The first string of 60 phototubes was successfully deployed on January 29, 2005. Below the lowest phototube of this string, Ryan Bay attached a dust logger we designed to read out depths of volcanic ash layers. By matching up those layers with layers to be recorded in other boreholes, we will be able to construct isochrones corresponding to the same eruptions. These contours will provide us with a three-dimensional map of optical properties of ice over the entire cubic kilometer of IceCube. As more strings are added, IceCube will take data in conjunction with the 19 strings of AMANDA detectors. IceCube and AMANDA together will form a single gigantic neutrino observatory, taking data for decades. See Snowmass for transparencies from a recent talk by Francis Halzen. See IceCube.karle.ppt for a recent talk by Albrecht Karle. For simulations of 10 TeV and 6 PeV muons and the "double bang" interaction of a 1 PeV tau neutrino, click here.
  1. The Ice-Cube High-Energy Neutrino Telescope, S. Yoshida for the IceCube Collaboration. Proc. 28th Intern. Cosmic Ray Conference, 1369-1372 (2003).

Optical Properties of Glacial Ice (papers in refereed journals):

  1. Optical Properties of Pure Ice at the South Pole: Scattering, P. B. Price and L. Bergström, Applied Optics 36, 4181-4194 (1997).
  2. Optical Properties of Pure Ice at the South Pole: Absorption, L. Bergström, P. B. Price et al., Appl. Optics 36, 4168-4180 (1997).
  3. Implications of Optical Properties of Ocean, Lake, and Ice for Ultrahigh-energy Neutrino Detection, P. B. Price, Appl. Optics 36, 1965-1975 (1997).
  4. UV and Optical Light Transmission Properties in Deep Ice at the South Pole, P. Askebjer and the AMANDA collaboration, Geophys. Res. Lett. 24, 1355-1358 (1997).
  5. Remote Sensing of Dust in Deep Ice at the South Pole, Y. D. He and P. B. Price, J. Geophys. Res. 103 (D14) 17041-17056 (1998).
  6. Optical Properties of South Pole Ice at Depths from 1400 to 2300 meters, K. Woschnagg, P. B. Price et al., in Proceedings of the 26th ICRC, August 17-25, 1999, Salt Lake City, Utah, pp. 200-203.
  7. Temperature Dependence of Optical Absorption in Ice at 532 nm, Kurt Woschnagg and P. B. Price, Applied Optics 40, 2496-2500 (2001).
  8. Optical Properties of the South Pole Ice at Depths Between 0.8 and 1 Kilometer, P. Askeber et al. (AMANDA Collaboration). Science 267, 1147-1150 (1995).

Glaciology
Models of the flow of glacial ice in response to an applied stress (usually the downhill component of the gravitational force of overlying ice) are still phenomenological. Laboratory experiments have the double disadvantage that they must be carried out at higher stress than is typical in nature, and that the volume of ice is unrealistically small. Observations in nature have had the double disadvantage that they are almost always limited to temperate ice, in order to see observable flow on a reasonable time-scale, and that only the strain rate, not the stress, is observed. Dima Chirkin and undergraduate student Jeff Allen are using the AMANDA database of downward-going muons to map the three-dimensional strain rate of deep ice in a volume of ~0.02 km3. Their early result shows no significant shear strain after one year at a depth corresponding to a temperature of -29oC. In future, the group plans to collaborate with Neil Humphrey in a long-term study of strain rate as a function of stress (to be measured with stress cells frozen into ice at various depths as IceCube is built). That experiment would instrument a cubic kilometer of ice at temperatures from -50o to -20o.

Glaciology (papers in refereed journals):

  1. Mechanisms of Attenuation of Acoustic Waves in Antarctic Ice. P. B. Price, Nucl. Instr. Meth. A325, 346 (1993).
  2. Kinetics of Conversion of Air Bubbles to Air-Hydrate Crystals in Antarctic Ice, P.B. Price, Science, 267,1802-1804 (1995).
  3. Age vs Depth of Glacial Ice at South Pole, P. B. Price, K. Woschnagg, and D. Chirkin. Geophysical Research Letters 27, 2129-2133 (2000).
  4. Temperature Profile for Glacial Ice at the South Pole: Implications for Life in a Nearby Subglacial Lake, P. Buford Price et al., Proc. Natl. Acad. Sci. 99, 7844 (2002).

Grain-size Logger
The idea of using changes in mean sound speed with depth in glacial ice to estimate changes in c-axis was pioneered by Charles Bentley, Ken Taylor, and others in the 1970s. Sonic logging of boreholes to infer c-axis habits is now a useful tool. An essential prerequisite for a rigorous understanding of the flow of ice is knowledge of the variation of grain size with depth. Price's concept of a grain-size logger is based on a commercial acoustic televiewer, which has long been used to image discontinuities and fluids in boreholes in rock and sediment. His modification would shift interest from a borehole wall to the interior of the ice. A small fraction of the ultrasound emitted horizontally from the grain-size logger will traverse ice and be back-scattered at grain boundaries. Some of the energy will be absorbed by crystal dislocations. If logging is done at more than one frequency in the megahertz band, it should be possible to determine grain size, c-axis habit, and dislocation density as a function of depth (see graph). Such data would reduce by orders of magnitude the labor now required to measure grain size by conventional means (painstaking production of thin sections of ice and analysis of size and orientation in a polarizing microscope).

Paleoclimatology
The dust logger has been a fantastic success. At the 1000-meter borehole at Siple Dome, Antarctica, the dust logger produced a record of air bubbles, of glacial and interglacial dust concentrations, and of volcanic ash layers as thin as a few mm in vertical extent. Several abrupt jumps in the dust record signify abrupt climate changes in the region around Siple Dome. The dust log of the depths of occurrence of volcanic ash has made it possible for volcanologists to find those same layers in ice cores for chemical and isotopic study, even when they are almost invisible to the eye. At the 3054-meter borehole at Summit, Greenland, both the top half, containing air bubbles, and the bottom half, containing a superb record of dust concentrations, provide paleoclimate information that is immune to fractures of the segments of ice cores removed from the borehole. Dramatic changes in climate occurring within a few decades are recorded in the dust record. In the Price group, Ryan Bay has found evidence for correlations of the dust and volcanic record between the southern and northern polar regions. He has proposed a mechanism by which volcanoes emit particles rich in soluble iron which provide critical nutrients for phytoplankton in the southern oceans; they grow rapidly and extract carbon dioxide from the atmosphere, thus reducing this major greenhouse gas and triggering global cooling.

Bay has now included ice core records of sulfate emissions from volcanoes with dust logger records and has shown that: the record of volcanism at Siple Dome, Vostok Station, and Dome C in Antarctica correlates with abrupt climate change in glacial periods at a 95% to 99.8% significance level; that the volcanic sequences in the two hemispheres match at levels > 3 sigma; and that these candidate global events were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. His manuscript on this topic is under review.

  1. Rapid Optical Method for Logging Dust Concentrationvs Depth in Glacial Ice, P. Miocinovic, P. B. Price, and R. C. Bay, Applied Optics 40, 2515-2521 (2001).
  2. Climate Logging with a New Rapid Optical Technique at Siple Dome, R. C. Bay, P. B. Price, G. D. Clow, and A. J. Gow, Geophys. Res. Lett. 28, 4635 (2001).
  3. Ice Logging with Light and Sound, R. C. Bay, N. Bramall, and P. B. Price, EOS 84 (9) 77-82 (2003).
  4. Volcanic Ash Record in the Siple Dome Ice Core, N. W. Dunbar, A. Kurbatov, G. A. Zielinski, W. C. McIntosh, P. B. Price, and R. C. Bay. Proc. WAIS Conference (2003).
  5. Bipolar Correlation of Volcanism with Millenial Climate Change. R. C. Bay, N. Bramall, and P. Buford Price, Proc. Natl. Acad. Sci. USA 101, 6341-6345 (2004).
Life in Extreme Environments
In A Habitat for Psychrophiles in Deep Antarctic Ice, Price showed that suitably adapted microbial life can exist in ice at temperatures down to about -90 degrees Celsius, depending on the presence of acids or salts that are insoluble in the solid ice and that form liquid phases with low eutectic temperatures. Within a network of ion-rich liquid veins at the triple junctions of ice grains, microbes can move, extract energy via reduction-oxidation reactions of the ions, and utilize elements necessary for life (C, H, O, N, Fe, S, P,?). The metabolic rate is such a strong function of temperature that the sparse nutrients present in veins can sustain a fairly large population of microbes, nearly dormant, for hundreds of thousands of years. Several lines of evidence support this conjecture: Karen Junge, Jody Deming, and co-workers have imaged living microbes in veins in both sea ice and lake ice. A. Sharma et al. have grown microbes in artificial ice at a pressure ten times that at the deepest part of the Pacific Ocean and have shown that the microbes can move in liquid veins. Todd Sowers, Kramer Campen, and Richard Alley have argued that the best explanation of sharp excesses of certain gases such as N2O, CH4, and CO2 correlated in depth with excesses of dust particles is that they represent the products of microbial metabolism.

In a PNAS paper, we studied the temperature dependence of metabolic rates for microbial growth, maintenance, and survival. On an Arrhenius plot of log rate vs 1/T (in Kelvins), we showed that metabolic rates per cell of microbial communities fall into three groupings: a rate for unlimited exponential growth; a far lower rate for maintenance of community size; and a still lower rate for immobilized communities to barely survive, using only enough energy to repair macromolecular damage. The temperature dependences of the three groupings were characterized by similar activation energies, with values at a given temperature in the ratio ~106:103:1. The rate continued to follow the same Arrhenius lines even down to -40ºC with no indication of a cutoff. The rate for repairing damage by means of DNA-repair enzymes and protein-repair enzymes such as methyltransferase is comparable to the rate of spontaneous molecular damage, from which we inferred that a microbial community immobilized in shale or ice may survive for geologic time. In our recent study of the basal ice at GISP2 (bottom 13 m of the 3053-m ice core) we found a typical concentration of ~108 cells/cm3, of which ~98% were attached to micron-size clay grains. To our surprise, we found that the number of microbes per grain increased linearly rather than quadratically with grain diameter. In a manuscript to appear in PNAS, we explained that the linear relationship is evidence for an electron-shuttling process by which an immobilized iron-reducing microbe metabolizes with the help of molecule of fulvic acid or hydroquinone that carries an electron from the microbe into one of the many thin layers of water between clay lamella where it reduces an Fe3+ ion to Fe2+. In addition to Fe-reducers, we have mapped the vertical distribution of methanogens, using their F420-autofluorescence.

  1. DeepIce: Prospects for Microbiology at an Interdisciplinary Science and Technology Center. P. B. Price, Proc. SPIE, 3755, 198-207 (1999).
  2. A Habitat for Psychrophiles in Deep Antarctic Ice. P. B. Price, Proc. National Academy of Sciences, 97, 1247-1251 (2000).
  3. Life in Solid Ice?, P. B. Price, unpublished manuscript.
  4. Search for Microbes and Biogenic Compounds in Polar Ice using Fluorescence. R. Bay, N. Bramall and P. Buford Price, in Life in Ancient Ice, eds. S. O. Rogers and J. D. Castello (Princeton University Press, Princeton, NJ, 2002), in press.
  5. Life in Solid Ice on Earth and Other Planetary Bodies, P. B. Price, in Bioastronomy 2002: Life Amongst the Stars, ed. Ray Norris and Frank Stootman (Asttronomical Society of the Pacific, IAU Symposium Series, 2003, Symposium No. 213), pp 363-366.
  6. Temperature Dependence of the Metabolic Rates for Microbial Growth, Maintenance, and Survival. P. Buford Price and Todd Sowers. Proc. Natl. Acad. Sci. USA 101, 4631-4636 (2004).

Biospectrologger
A test of the biospectrologger (BSL) in Lake Tahoe has produced a clear record of the vertical distribution of chlorophyll, due to phytoplankton, as well as a probable record of fluorescence from NADH, present in all living cells. The chlorophyll intensity went through a maximum at a depth of ~50 m, whereas the NADH signal monotonically increased with depth, in rough agreement with measurements made on water recovered from various depths. Nathan Bramall has redesigned the BSL so that it is now sensitive to a microbial concentration as low as ~1 cell/cm3, provided the instrument is used in an air-filled or water-filled borehole. (Organic borehole fluid has aromatic impurities that provide an unacceptably high background of fluorescence.) In January 2004, Bramall deployed the new BSL, with a 224 nm laser, in a 250-m air-filled borehole some 8 km from South Pole. With it he was able to record the depth dependence of tryptophan fluorescence, showing that the concentration of microbes was a maximum at roughly the base of the firn layer at ~120 m and then decreased monotonically with depth down to 250 m. The first of our NASA ASTEP grants is to design and build a miniaturized BSL that will fit into a 5-cm borehole in ice, permafrost or rock. A version with a 224-nm laser will be ready for use in March 2005. We will deploy it in the ice-covered Lake Vida in the Dry Valleys, Antarctica. The second NASA grant is to build a scanning spectrofluorimeter to map microbes in near-surface glacial ice over much of the ice-covered Antarctic continent. Click on ASTEP.ppt to see a powerpoint presentation on the two projects. We hope to use one of these instruments in a borehole in Martian permafrost or on a rover. Thinking farther into the future, we envisage using a miniaturized BSL to search for microbial life in ice on Jupiter's moon, Europa.

Sizing of individual Bacillus spores
Andrew Westphal and Price have used automated scanning microscopy to study various species of Bacillus, which sporulate (convert to spores) when conditions become hostile. In the first set of experiments, we found that Bacillus thuringiensis spores, despite being dormant, rapidly expand or shrink in size in response to an abrupt change in humidity. In followup work, we found that spores of different species of Bacillus have slightly different sizes and swelling amplitudes. On a plot of size at 0% relative humidity vs increase in size for an increase from 0% to 100% relative humidity, the species cluster in different regions of the plot. These encouraging results led us to suggest that automated measurements may some day make possible the identification of Bacillus anthracis in dust from air or from a central mail room.

  1. Kinetics of Size Changes of Individual Bacillus thuringiensis Spores in Response to Changes in Relative Humidity, A. J. Westphal, P. B. Price, T. J. Leighton, and K. E. Wheeler, Proc. Natl. Acad. Sci., 100, 3461-3466 (2003).

Biographies
The National Academy of Sciences publishes an annual volume of biographies of deceased members. See my biographies of John Reynolds, a former member of the Berkeley Physics Department, and of Bob Walker, a physicist with whom I collaborated in the 1960s.

Links of interest:
South Pole Station
The New South Polar Times
AMANDA manuscripts