Systematic investigations of the nuclear level structures of stable heavy transitional nuclei are being performed by (n, n'.gamma.) reaction spectroscopy. Detailed .gamma.-ray excitation functions and angular distributions permit characterization of low-lying states, with particular emphasis on understanding collective excitations of both positive and negative parity. Questions regarding nuclear shapes, deformation effects, and the applicability of various nuclear models to these nuclei have been addressed. Completed studies of 194Pt and 198Pt reveal significant structural differences between these nuclei, and have led to studies of other transitional nuclei as the next step in a comprehensive examination of this mass region. Cross section systematics for the (n, n'.gamma.) reaction are being developed and, where possible, .gamma.-ray studies have been complemented by neutron detection time-of-flight measurements. 6 figures, 1 table.

This report summarizes progress during the past year in the following areas of nuclear structure and reaction theory: statistical spectroscopy (including random matrix methods, with applications to fluctuations in spectra and in strength distributions, and to problems of ergodicity; group symmetries in spectral-distribution theory; electromagnetic and .beta. transitions); meson scattering and absorption by nuclei (including general scattering theory with absorption, multiple scattering theory and its reactive content, statistical theory of absorption); and meson currents in electromagnetic transitions.

Sections 1-2. Keyword Index.--Section 3. Personal author index.--Section 4. Corporate author index.-- Section 5. Contract/grant number index, NTIS order/report number index 1-E.--Section 6. NTIS order/report number index F-Z.

Activities of the period August 1, 1979 through July 31, 1980 are reviewed. The results from the relativistic heavy-ion central collisions from the Bevatron are updated, and now represent the most recent evaluation of an energy scan in a search for phase transitions in nuclear matter. The effective cross section for the pion production and additional information, incuding the multiplicity distributions and .pi.-.pi. correlations, are obtained. Preparation is underway for an approved experiment using heavier projectiles at the Bevalac, searching for the unusual production of high energy gamma-rays and lepton pairs as signatures for neutral mesons. The importance of such events as an evidence of the onset of phase transition is discussed. A brief summary is given for an alpha-alpha collision experiment at the CERN ISR in the search for unusual behavior in secondary hadron production. The measurement of the pionic x-rays using a bent crystal spectrometer is now analyzed to yield the new value for pionic mass, and upper limit for the muonic neutrino mass. Preparation is underway for the approved experiment at the TRIUMF for the study of the neutron and gamma ray correlation in .pi. capture. 18 figures, 5 tables. (RWR).

Research during the period November 1979 through October 1980 is reported. Completed work will be published in the usual places. Three sections containing significant amounts of information are abstracted separately. (RWR).