and astrophysics, including plasma physics, atomic physics, nuclear physics, radiative transfer, properties of matter, cosmology, and the physics of the early universe. The opportunity is great for fruitful cross-fertilization between astrophysics and the laboratory-oriented physics that is supported by the DOE.

PARTICLE ASTROPHYSICS

The study of solar neutrinos contributes to our understanding of stellar interiors and of fundamental physics. The discrepancy between the predicted rate of solar neutrino production and the values measured in the Homestake mine since the 1960s, and recently confirmed by the Japanese Kamiokande II experiment, has raised important questions for both astrophysics and particle physics. The first preliminary answers to these questions will become available in the 1990s from the Soviet-American and Western European-Israeli-American experiments using gallium detectors.

The important new experimental results are being obtained using neutrino observatories in other countries, including Canada (Sudbury), Italy (Gran Sasso), Japan (Kamiokande), and the Soviet Union (SAGE), although many of the experimental techniques and theoretical ideas were developed in the United States. However, the international collaborations are strong, and some involve talented American scientists working at the frontiers of research. The committee recommends in Chapter 1 the development of the technology for a new generation of U.S. solar neutrino experiments (see Table 1.3). These detectors would also be sensitive to supernova neutrinos.

  • The committee urges the DOE and NSF to continue to support American participation in international solar neutrino experiments.

The serendipitous detection of neutrinos from Supernova 1987A confirmed the basic ideas of stellar collapse, including the order of magnitude of the total neutrino energy emitted, the time scale for the neutrinos to escape, and the characteristic energy of an individual neutrino. Only about 20 neutrinos were detected, but the observation validated theoretical insights that originated more than half a century ago. More diagnostic measurements can be made of future supernovae with detectors designed specifically for this purpose.

Two fundamental programs in particle astrophysics involve the detection of particles with very high energies: gamma rays with energies in the range 1011 to 1014 eV and cosmic rays up to 1020 eV. The Whipple Observatory of the Smithsonian Institution has detected gamma rays above 3 × 1011 eV from the Crab Nebula, and there are possible detections from other observatories of even higher energies from x-ray binary stars. The “Granite” telescope, currently under construction at Mt. Hopkins, will have improved sensitivity to radiation with energies up to 1012 eV. Upgraded airshower facilities at Los



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