Inclusive cross sections for positive pion absorption leading to final states including two or more protons have been measured with a large solid angle detector for incident pion energies from 30 to 135 MeV for targets with A=2-208. The mass dependences for the inclusive ( pi(+),2p), ( pi(+),3p), and total absorption cross sections for multiproton final states were found to be proportional to A(n) with n approximate to 0.5. These cross sections also were observed to have an energy dependence at energies below 150 MeV reflective of the importance of the Delta(1232) resonance, similar to that observed for pi d-->pp. The inclusive cross sections for ( pi(+),4p) were found to be less than 10 mb for all targets at all energies. Estimates were also obtained for cross sections for pion absorption leading to 2p 1n and 3p 1n final states. Quasideuteron absorption contributions increase slowly with A, and the energy dependence of those contributions mirrors that for pi d-->pp. The data obtained here for multiproton final states indicate that a significant fraction of absorption events, increasing with A, most likely arises from final states containing fewer than two protons.

Double charge exchange cross sections for 50 MeV pions to double isobaric analog states in Ca-44, Fe-56, and Nb-93 were measured. The results indicate that the effective double charge exchange operator at this energy has a strong short-range component. In addition, evidence is presented tending to implicate isospin mixing as the mechanism for excitation of the analog of the antianalog in Nb-93.

Measurements have been made for reactions involving positive pions incident on CD{sub 2}, {sup nat}C, {sup 6}Li, {sup 27}Al, {sup 58}Ni, {sup 118}Sn, and {sup 208}Pb at 8 energies from 30 to 135 MeV. The experiment was performed at the Clinton P. Anderson Meson Physics Facility (LAMPF) Low Energy Pion channel using the large solid angle, 30-element bismuth germanate phoswich {open_quotes}BGO Ball{close_quotes} detector with a downstream CsI detector array. Preliminary results from the analysis of the data for the total cross sections for the ({pi}{sup +}, 2p) reaction on the above nuclei will be presented. A parameterization for the energy mass dependence will be discussed.

Differential cross sections for 40, 50, and 65 MeV ${\mathrm{\ensuremath{\pi}}}^{+}$ and ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ inelastic scattering to ${1}^{\mathrm{\ensuremath{-}}}$ excitations in $^{12}\mathrm{C}$ have been measured and compared to distorted wave impulse approximation (DWIA) reaction model predictions. Strengths are presented in terms of sum rules for the ${1}^{\mathrm{\ensuremath{-}}}$ state at 10.84 MeV and for the giant dipole resonance from 18 to 25 MeV. An excitation function at q=224 MeV/c for the ${1}^{\mathrm{\ensuremath{-}}}$ state at 10.84 MeV is displayed in the energy range from 50 to 291 MeV showing a non-spin-flip pattern. We find inadequacies in the detailed comparison of the shapes of the data to DWIA calculations using several standard nuclear models.

Differential cross sections for 40, 50 and 65 MeV pi+ and pi- inelastic scattering to 1- excitations in 12 C have been measured and compared to distorted wave impulse approximation (DWIA) reaction model predictions. Strengths are presented in terms of sum rules for the 1- state at 10.84 MeV and for the giant dipole resonance from 18 to 25 MeV. An excitation function at q =224 MeV/c for the 1- state at 10.84 MeV is displayed in the energy range from 50 to 291 MeV, showing a non-spinflip pattern. We find inadequacies in the detailed comparison of the shapes of the data to DWIA calculations using several standard nuclear models.

The SCRUNCHER is a superconducting radio-frequency cavity for manipulating the longitudinal phase space of the secondary pion beam from the low energy pion channel at LAMPF. Test results of the cavity performance and initial results from in-beam tests are presented.

During ODP Leg 103, serpentinized peridotite (clinopyroxene-spinel harzburgite) was cored within the basement approximatively at the boundary between the North Atlantic oceanic curst to the west, and the thinned continental crust of the Galicia passive margin (Spain) to the east. The exposure of mantle derived peridotite on the seafloor occurred at the end of the period of rifting, roughly 110 Ma ago. Ductile shear zones observed in the cored peridotite are consistent with movements along a deep low-angle, normal fault rooted within the upper mantle and dipping eastward, beneath the Galicia margin. To explain the tectonic denudation of the mantle at the ocean-continent boundary, we use a non-uniform stretching model for the lithosphere, set up from the Wernicke's model (1985).

La campaña oceanográfica 103 del Ocean Drilling Program (ODP) ha estado dedicada a dilucidar la evolución tectónica y sedimentación del Margen Atlántico-Ibérico. Se realizaron un total de 14 sondeos., en cinco puntos de posicionamiento, sobre el extremo más profundo del margen; al S del Banco de Galicia. Los resultados obtenidos revelan que previamente al inicio de la expansión oceánica entre Terranova e Iberia ocurrió una historia compleja de distensión cortical, fracturación y subsidencia asociadas. Los resultados fundamentales son los siguientes: 1) Carbonatos de plataforma marina somera, de edad Jurásico superior-Cretáceo basal constituyen los primeros depósitos mesozóicos en ese ámbito del margen y dan lugar a un reflector sísmico considerado interiormente como basamento, 2) El hundimiento de la plataforma, fallamiento y basculamiento de los bloques ocurre desde 25 m.a. antes de iniciarse la acreción oceánica. 3) En el límite entre corteza oceánica-corteza continental se ubica una cresta constituida por peridotitas serpetinizadas. 4) El reflector sísmico «S», generalmente considerado como el límite dúctil-frágil en la corteza continental, corresponde realmente a la base de los depósitos sinrift.

Results of drilling near the ocean-continent boundary on the Galicia margin of Iberia shed new light on the timing of rifting and demonstrate the presence at the foot of the margin of a ridge of foliated, lineated, sheared and serpentinized harzburgite, probably representing oceanic mantle. Fifty km east of the periodotite ridge, on a continental fault block, the stratigraphic section sampled during Leg 103 above Hercynian basement comprises: (1) at least 250m of Upper Jurassic and possibly lowest Cretaceous limestone, dolomite and minor sandstone and claystone deposited in relatively shallow water before rifting began; (2) about 20m of Valanginian calpionellid marlstone, probably deposited in moderate depths at the onset of rifting; (3) from about 500 to 1500m of Valanginian and Hauterivian turbidite sandstone rich in terrestrial plant debris, and Barremian and Aptian( ) claystone and marlstone deposited in deeper water during rifting; and (4) about 700m of sediments deposited after Aptian time, when rifting ceased and oceanic spreading between Iberia and Newfoundland began. The lithology and seismic stratigraphy of the wedges of clastic sediments laid down during rifting show the progressive filling of basins that formed by episodic listric faulting that began very early in the Cretaceous and continued formore » about 25 my. The Lower Cretaceous turbidite sandstone cored on the Galicia margin correlates with thick Lower Cretaceous turbidites cored off Morocco during DSDP Leg 50, and with Wealden deltaic and fluviatile deposits on both sides of the Atlantic.« less