[en] The elastic and inelastic scattering of π⁺ and π^- by ¹³C, ¹⁶O, and ¹⁷O was studied at pion energies close to the (3,3) resonance. Data were taken at the Los Alamos Meson Physics Facility. Large asymmetries were observed, two of which are consistent with pure neutron and pure proton excitations. Transitions to strongly excited states of ¹³C are in strikingly good agreement with theoretical predictions of Lee and Kurath. In sharp contrast, strong disagreements are found for the weakly excited states. The asymmetries for ¹⁶O + π^+- were interpreted as due to isospin mixing between the excited states. High-resolution data for (t,t') and (³He,³He') on ¹³C were taken to supplement the pion work. Asymmetries were found for the relative cross sections for some states. In studies of the heavy-ion-nucleus potential the effect of potential resonances on the elastic scattering of ¹⁶O + ²⁸Si was found to be small. A close similarity between the elastic exchange amplitude at 180⁰ and the effect of the parity dependence on the elastic amplitude was found. Fits to the new data at 40 and 41.226 MeV required the use of a composite absorptive potential. The surface derivative part of this potential can be deduced from a coupled-channels calculation. 17 figures

[en] A large number of experiments were done using pion and proton beams at intermediate energies to investigate different excitation modes of the nucleus. Pions were found to be especially suited to excite magnetic transitions of high multipolarity (M4's). The isospin, or neutron/proton, structure of many transitions could be unraveled and detailed comparisons with the predictions of large-space shell-model calculations were successful in many cases. A few glaring exceptions were found to the general good agreement between theory and experiment. For the collectively enhanced electric quadrupole (E2) and octupole (E3) transitions, effective charge enhancements were needed to fit the pion and proton data. The polarization charges were usually found to be in good agreement with the results of electromagnetic measurements. Studies of the excitation of giant resonances by pion inelastic scattering indicated a large isovector component in the transitions to isoscalar giant resonances. This result, although theoretically unexpected, is supported by comparison of electron and alpha-particle scattering and requires further study. A very recent experiment on pion inelastic scattering from ⁴He showed little evidence for isospin mixing in this nucleus, in contrast to the conclusions drawn from (γ,n) and (γ,p) work. A high precision elastic π⁺ scattering experiment on ⁴He is underway. The work on heavy-ion elastic scattering was completed and terminated. Two experiments are presently being done at lower energies to supplement the work at intermediate energy

[en] A list of the experimental programs at the Los Alamos Meson Physics Facility is given. In addition, the personnel associated with these programs are listed

[en] π-meson and proton beams from the Los Alamos Meson Physics Facility (LAMPF) and the Indiana University Cyclotron Facility (IUCF) were used in scattering and reaction experiments on atomic nuclei. The experimental data allow tests of models of the reaction mechanism and of nuclear structure. For example, the asymmetries observed in a pion scattering experiment on polarized ¹³C nuclei were found to contain unique information on the isoscalar spin density. However, further experiments on polarized nuclei of simpler structure are needed to provide the data for a thorough analysis of the reaction mechanism. For this reason a pion scattering experiment on a polarized ³He target is planned and a high-resolution study on ⁶Li(π,π') will be done. An analysis of π-triton coincidence events from the ⁴He(π,π't)p reaction yielded evidence for direct triton knock-out from ⁴He. This work will be continued at higher incident pion energies. Additional work on the ⁴He(p,n) reaction at IUCF is planned to determine the isovector strength in mass-4 nuclei and the level parameters of ⁴Li

[en] This paper discusses the following topics: pion scattering from polarized ¹³C; elastic scattering of π⁺ and π^- from ⁴He; the ⁴He(π,π,t)p and ⁴He(π,π,d) reactions; contributions to the planning of PILAC; and the ⁴He(p,n)⁴Li reaction at 100, 147, and 200 MeV

[en] Three experiments on pion inelastic scattering were performed during the last year at the Los Alamos Meson Physics Facility. Data reduction for the ¹⁴C experiment is complete and new information on the M4 strength in this nucleus was extracted. Data reduction for the ¹⁶O and ¹⁷O experiments is underway. Theoretical analyses of earlier data were continued and work on a consistent description of (π,π'), (e,e'), and (p,p') experiments on ¹⁶O and ¹³C proved to be very encouraging. In an experiment at the Swiss Institute for Nuclear Research (π,π'γ) angular correlation data were taken for the first time. The results support present theories on the importance of Δ-nucleus dynamics in pion scattering

[en] The analysis of a large number of experiments has been completed. Among these are the studies of magnetic transitions by inelastic pion scattering on ¹⁴C, ¹⁵N, and ⁴⁸Ca, and the octupole transitions in ¹⁷O. The experimental data provided stringent tests of large-space shell model calculations. Progress was made in the study of M1 transitions by proton scattering and in searches for evidence of a charge symmetry breaking force larger than the Coulomb force. Inelastic scattering of π⁺ and π^- from ⁴He yielded π⁺/π^- asymmetries completely consistent with isospin mixing due to the Coulomb force alone in sharp contrast to the conclusions drawn from photo-nucleon reactions. A study of π⁺ and π^- scattering to the first 2⁺ states in nuclei between A = 18 and 42 revealed a systematic difference between the neutron transition matrix elements M/sub n/(T/sub z/ = +1) in the target nuclei and the proton matrix elements M/sub p/(T/sub z/ = -1) in the mirror nuclei although charge symmetry predicts M/sub n/(+1) = M/sub p/(-1). The work on the pion-nucleus reaction mechanism was continued by investigating the importance of two-step processes by coupled-channels calculations. Publications are listed

[en] A major effort was made in the study of proton and pion induced reactions on ⁴He. Spin transfer observables were measured for the first time for the ⁴He(/rvec p/,/rvec p/') reaction at 500 MeV at the Los Alamos Meson Physics Facility. The preliminary results show a spin-flip probability in the continuum of ⁴He which is much larger than the free proton-proton scattering value. The group also collaborated in the related ⁴He(/rvec p/,p'X) work done at the Indiana University Cyclotron Facility. The work on data reduction of the ⁴He(π^+-,π^+-'p) and ⁴He /plus/ π/+-/ elastic scattering experiments was continued and new data were taken for ¹²C(π^+-,π^+-p). A new analysis of 2⁺ states in ¹⁴C excited by π/sup /plus//, π/sup /minus//, and proton scattering was performed using large-space shell model calculations

[en] Experiments performed at the Los Alamos Meson Physics Facility yielded very striking results. In inelastic pion scattering from ¹⁴C near the [3,3] resonance cross sections ratios R = sigma(π⁺)/sigma(π^-) and R^-1 = sigma(π^-)/sigma(π⁺) were observed that are significantly larger than the free pion-nucleon values. These results were interpreted as due to strong cancellations of the neutron and proton components in the transition amplitude. Measurements of ¹³C(π,π') excitation functions between 100 and 300 MeV at two momentum transfers showed dramatically different energy dependencies for ΔS =0 and ΔS = 1 transitions. They were used to derive nuclear structure information on several highly excited states. Pion data for other nuclei (¹²C, ¹⁶O, ⁴⁰Ca, etc.) were analyzed and information on isospin mixing, the double-charge-exchange reaction mechanism, and the excitation of collective states was extracted. Further data were taken with a 547 MeV proton beam on ¹³C. The data taking for the (t,t') and (³He,³He') reactions at the Los Alamos Van de Graaff has been completed. The continuing studies of the heavy-ion nucleus optical potential yielded information on very systematic dependencies of the potential depths on the incident energy

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