The Nuclear Physics Laboratory of the University of Washington has for over 40 years supported a broad program of experimental physics research. The current program includes "in-house" research using the local tandem Van de Graaff and superconducting linac accelerators and non-accelerator research in solar neutrino physics at the Sudbury Neutrino Observatory in Canada and at SAGE in Russia, double beta decay and gravitation as well as user-mode research at large accelerator and reactor facilities around the world.

The Mass-8 experiment has made significant progress by nearly doubling the amount of data for both ⁸Li and ⁸B beta decay. Monitoring of the gas counter performance was added to insure the quality of the data. The new high energy gamma ray beamline and detector setup has been completed and first data have been taken toward obtaining a precise spectrum of photons from the 17 MeV excited states of ⁸Be.

As an important step in interpreting GDR emission spectra, a measurement of pre-equilibrium particle loss prior to compound nuclear formation was made for 200 MeV ¹⁸O + ¹⁰⁰Mo. The result is, on average, a compound nucleus that is 3 mass units lighter and 20% lower excitation energy than the compound nucleus formed in complete fusion.

In a study of sub-barrier fusion of Ca with Ti isotopes it has been shown that quasi-elastic scattering excitation functions can be used to obtain barrier distributions with similar structure to that obtained from fusion data.

We have measured the angular distribution of fission fragments in various near- and sub-barrier heavy-ion reactions with actinide targets. We find no evidence of strong peaklike structures in fission fragment anisotropies as a function of center-of-mass energy. An analysis of C+U and O+Th fission fragment anisotropies yields no evidence of an effect due to the entrance channel mass asymmetry. A study of the three reactions C + ^235,236,238U indicates a strong influence of the ground state spin of actinide targets on the anisotropy of fission fragments at sub-barrier energies.

A coincidence study of the fragmentation of C₆₀ (buckyballs) in collisions with hydrogen has demonstrated that near-binary fragmentation competes with dimer evaporation in producing fragments in the C₄₀ to C₅₀ mass range. Also, a new pathway for producing doubly negative carbon clusters by fragmenting alkali carbide anions has been demonstrated.

Our development of beryllium targets for a planned  experiment has achieved a ⁹Be target, fabricated in the same manner as will be used eventually to make a ⁷Be target, with an impurity/Be ratio of 2/1.

The Russian-American Gallium Experiment (SAGE) has published the results from a successful ⁵¹Cr neutrino source experiment. Analysis of the solar neutrino results is near completion.

Work continues at a rapid pace toward completion of the Sudbury Neutrino Observatory. Following four years of planning and development, installation of the acrylic vessel is now over 60% complete, with final completion scheduled for this fall. The UW SNODAQ group has prototyped most of the software elements necessary for the SNO data acquisition, and has made significant progress in the coding of the online data-monitoring system. The code needed for bulk testing of the production front-end electronics is mostly in place. MiniSNO has been used to test the electronics calibration algorithms, and will be used again in the near future to test some of the optical calibration sources. The Neutral-Current Detector project has also made great strides in the last year with production of prototype counters. Preamplifiers, endcaps, cable terminations and delay lines for the proportional counters are being assembled. We have received the majority of the required CVD Ni tubing. The assembly equipment is ready and the production phase will begin soon. We have taken delivery of the remotely operated submersible vehicle to be used to deploy the neutral current detectors in the acrylic vessel.

A successful run on the parity nonconserving neutron spin-rotation in ⁴He was carried out on the NG-6 beamline at the Cold Neutron Research Facility at NIST in Gaithersburg, MD. In December, the emiT experiment, a search for time-reversal violation in neutron beta decay of free neutrons, moved onto this beamline. The emiT system, which includes four beta and four proton detectors segments as well as beam and spin transport systems, observed first data in early January and is scheduled to continue to acquire data through mid-1997.

A new algorithm for simulating the effects of multiparticle Bose-Einstein statistics and Coulomb interactions in ultrarelativistic heavy ion collisions at NA49 and STAR has been implemented in a code that is now being tested and will be used to generate a library of Bose-Einstein correlated events simulating collisions at CERN and RHIC.

New limits for short range equivalence principle violations have been obtained with the rotating source torsion balance apparatus. A new continuously rotating torsion balance apparatus to test the equivalence principle for a variety of sources that are as exotic as dark matter is under construction.

As always, we encourage outside applications for the use of our facilities. As a convenient reference for potential users, the table on the following page lists the vital statistics of our accelerators. For further information, please write or telephone Professor Derek W. Storm, Director, Nuclear Physics Laboratory, University of Washington, Seattle, WA 98195; (206) 543-4085 (e-mail; STORM@NPL.WASHINGTON.EDU).

We close this introduction with a reminder that the articles in this report describe work in progress and are not to be regarded as publications or to be quoted without permission of the authors. In each article the names of the investigators have been listed alphabetically, with the primary author to whom inquiries should be addressed underlined.

We thank Richard J. Seymour and Karin M. Hendrickson for their help in producing this report.

Kurt Snover

Editor

Barbara Fulton

Assistant Editor