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Compression effects in relativistic nucleus-nucleus collisions (1982)

Reinhard Stock R. Bock R. Brockman J. W. Harris A. Sandoval Herbert Ströbele K. L. Wolf H. G. Pugh L. S. Schroeder M. Maier R. E. Renfordt A. Dacal M. E. Ortiz

The negative-pion multiplicity is measured for central collisions of 40Ar with KCl at eight energies from 0.36 to 1.8 GeV/nucleon and for 4He on KCl and 40Ar on BaI2 at 977 and 772 MeV/nucleon, respectively. A systematic discrepancy with a cascade-model calculation which fits proton- and pion-nucleus cross sections but omits potential-energy effects is used to derive the energy going into bulk compression of the system. A value of the incompressibility constant of K=240 MeV is extracted in a parabolic form of the nuclear-matter equation of state.

Parity of bound dipole states in 208Pb (1982)

K. Wienhard K. Ackermann K. Bangert U. E. P. Berg C. Bläsing W. Naatz A. Ruckelshausen D. Rück R. K. M. Schneider Reinhard Stock

The parities of eleven J=1 levels in 208Pb were determined by nuclear resonance fluorescence scattering of linearly polarized photons. A new 1+ level at Ex=5.846 MeV with Gamma 02 / Gamma =1.2±0.4 eV was found. This level can probably be identified with the theoretically predicted isoscalar 1+ state in 208Pb. All other bound dipole states below 7 MeV with Gamma 02 / Gamma >1.5 eV have negative parity. The 1- assignment to the 4.842-MeV level is of special significance because of previous conflicting results about its parity.

16O( gamma ,p) 15N reaction with linearly polarized photons (1981)

K. Wienhard R. K. M. Schneider K. Ackermann K. Bangert U. E. P. Berg Reinhard Stock

The 16O ( gamma ,p0) reaction has been studied with linearly polarized bremsstrahlung photons in and below the giant E1 resonance. The parity of the absorbed radiation was determined from the observed azimuthal asymmetry of the emitted protons. Combined with unpolarized measurements the polarized results determine the proton decay amplitudes of the M1 resonance at Ex=16.2 MeV in 16O. The shape of the unpolarized 16O ( gamma ,p3) angular distribution in the giant E1 resonance was derived from the measured analyzing power. NUCLEAR REACTIONS 16O( gamma ,p), E=15-25 MeV; measured analyzing power theta =90° linearly polarized bremsstrahlung; 16O dipole levels deduced pi ; 16.2 MeV 1+ resonance deduced p0 decay amplitudes; 16O GEDR deduced p3 angular distribution.

11 262 keV 1+ state in 20Ne (1983)

U. E. P. Berg K. Ackermann K. Bangert Reinhard Stock K. Wienhard

The excitation energy of the lowest 1+, T=1 state in 20Ne, which is important for parity nonconservation studies, has been determined in a photon scattering experiment to be 11 262.3 ± 1.9 keV. Values for the gamma -ray branching of this level to the ground state and to the first 2+ level in 20Ne are 84 ± 5% and 16 ± 5%, respectively. NUCLEAR REACTIONS 20Ne( gamma , gamma ), E gamma <18 MeV, bremsstrahlung; measured E gamma , gamma branching. Ne natural targets.

Emission patterns in central and peripheral relativistic heavy-ion collisions (1980)

Reinhard Stock H. H. Gutbrod W. G. Meyer A. M. Poskanzer A. Sandoval J. Gosset C. H. King G. King Ch. Lukner Nguyen Van Sen Gary D. Westfall K.L. Wolf

Proton emission in relativistic nuclear collisions is examined for events of low and high multiplicity, corresponding to large and small impact parameters. Peripheral reactions exhibit distributions of protons in agreement with spectator-participant decay modes. Central collisions of equal-size nuclei are dominated by the formation and decay of a fireball system. Central collisions of light projectiles with heavy targets exhibit an enhancement in sideward emission which is predicted by recent hydrodynamical calculations.

Contribution of alpha cluster exchange to elastic and inelastic 16O + 20Ne scattering (1976)

Reinhard Stock U. Jahnke D. L. Hendrie J. Mahoney C. F. Maguire W. F. W. Schneider D. K. Scott G. Wolschin

Angular distributions for elastic and inelastic transitions in 20Ne + 16O scattering have been measured at E(20Ne)=50 MeV. For the 0+, 2+, and 4+ members of the 20Ne ground-state rotational band, the angular distributions exhibit pronounced backward peaking characteristic of an alpha -cluster exchange mechanism. The analysis of the ground-state transition in the first-order elastic transfer model yields no satisfactory fit although microscopic cluster form factors and full recoil corrections are employed. A coupled channels calculation for the 0+, 2+, and 4+ transitions reveals very strong coupling effects, indicating that the coherent superposition of first-order optical model and distorted-wave Born-approximation amplitudes may not be an adequate model for these reactions. NUCLEAR REACTIONS 16O(20Ne, 16O) and 16O(20Ne, 20Ne), elastic and inelastic transfer; E=50MeV; measured sigma (Ef , theta ); optical model + DWBA, and CCBA analyses.

Excitation of Rotational Bands in 40Ca Observed in the Reaction 36Ar(16O, 12C) (1972)

Peter Braun-Munzinger Claus-Konrad Gelbke N. Grama Heinrich Homeyer E. Ridinger Reinhard Stock

Levels strongly populated in the reaction 36Ar(16O, 12C)40Ca are compared with predictions for the lowest (oblate) 4p-4h rotational band in 40Ca.

Anomalous Backward alpha Scattering (1972)

Reinhard Stock G. Gaul R. Santo M. Bernas B. Harvey D. Hendrie J. Mahoney J. Sherman J. Steyaert M. Zisman

The elastic alpha scattering to backward angles has been studied for 40,42,44,48Ca between 40.7 and 72.3 MeV. The cross sections for 40Ca are larger than those for the higher isotopes up to the highest energies. They show backward increases that disappear above 50 MeV. The enhancement factor for 40Ca over 42,44Ca varies smoothly with energy. 48Ca does also show a backward cross-section enhancement over 42,44Ca. alpha -cluster rotational bands in the 44Ti compound state, four-nucleon correlations in 40Ca, and the l-dependent optical model are discussed as approaches to understand the anomaly. The rotator model appears to agree qualitatively with the experimental data. It involves rotational bands extending at least up to J=16 in 44Ti.

Shell-Structure Effect on Elastic alpha Scattering (1972)

H. Oeschler H. Schröter H. Fuchs L. Baum G. Gaul H. Lüdecke R. Santo Reinhard Stock

Back-angle enhancements of elastic alpha -scattering cross sections have been observed for nuclei at the ends of the 1p, 2s-1d, and f7 / 2 shells. Strong reduction of this enhancement occurs if excess neutrons enter the next open major shell. The results are discussed in terms of intermediate alpha structure.

Pion Production in the 40Ar+40Ca Reaction at 1.05 GeV/Nucleon (1979)

K. L. Wolf H. H. Gutbrod W. G. Meyer A. M. Poskanzer A. Sandoval Reinhard Stock J. Gosset C. H. King G. King Nguyen Van Sen Gary D. Westfall

Pion-production cross sections have been measured for the reaction 40Ar+40Ca--> pi ++X at a laboratory energy of 1.05 GeV/nucleon. A maximum in the pi + cross section occurs at mid-rapidity, which is anomalous relative to p+p and p+nucleus reactions and compared to many other heavy-ion reactions. Calculations based on cascade and thermal models fail to fit the data.

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