W. Mittig

Model-unrestricted nucleus-nucleus scattering potentials from measurement and analysis of 16O + 16O scattering☆

Abstract The elastic scattering cross section for 16 O ions on 16 O targets has been measured with high accuracy over large angular ranges at incident energies from 250 to 704 MeV. From these data which sample both diffractive and refractive scattering processes, we extract the underlying scattering potentials using model-unrestricted analysis methods. The extracted potentials fit very well into the systematics found in light-ion scattering. The real potential parts also compare very favourably with microscopically calculated folding potentials based on a weak density-dependence of the underlying effective nucleon-nucleon interaction at large overlap densities.

Heavy ion charge exchange reactions to probe the giant electric isovector modes in nuclei

Abstract The ( 13 C, 13 N) reaction has been studied at E / A = 50 MeV/u on 12 C, 40 Ca, and 58 Ni targets at extremely forward angles including zero degree. Strong excitation of the ΔT z = + 1 analog of the giant dipole resonance is observed, and its angular distribution measured over the range 0° θ lab

The mechanism of the (12C,12N) charge exchange reaction on 12C between 30 and 100 MEV/U

Abstract The Charge exchange reaction 12 C( 12 C, 12 N) 12 B has been studied at 30 and 70 MeV/u in order to investigate the energy dependence of the two reaction mechanisms involved: the direct charge exchange and the proton-neutron exchange. Microscopic calculations have been performed for both processes and an almost quantitative description of the data could be achieved. The p-n exchange is strong at low energies and has a maximum at about 30 MeV/u. The direct process dominates for all states only at energies well above 100 MeV/u, but the energy region for the transition from two-step to direct dominance is strongly state dependent.

The equation of state for cold nuclear matter as seen in nucleus-nucleus scattering

SummaryThe equation of state for cold nuclear matter is determined by the effective, density-dependent interaction between bound nucleons at temperatureT = 0. This interaction can be probed in elastic nucleus-nucleus collisions at various density overlaps which may extend to several times the normal matter density. For this purpose the elastic scattering of16O ions on16O has been measured at incident energies from 250 to 1120 MeV with high accuracy. From these data, which sample both diffractive and refractive scattering processes, we extract the underlying scattering potentials utilizing model-unrestricted analysis methods. These potentials fit very well into the systematics found in light-ion scattering and compare very favorably with microscopic calculations, if these are based on a weak density dependence of the effective NN interaction, resulting in a soft equation of state for cold nuclear matter.

Anomalous heavy ion scattering near the Coulomb barrier

Abstract Striking oscillations were found in the elastic scattering of 12 C + 24 Mg near the Coulomb barrier. These oscillations are not reproduced by the standard potentials at higher energies and provide the determination of the optical potential without continuous ambiguity. The dispersion relation between the real and imaginary parts of this optical potential is not satisfied at the strong absorption radius, but holds for their volume integrals.

Study of refractive structure in the inelastic O16+O16 scattering at the incident energies of 250 to 1120 MeV☆

Abstract The data of inelastic O 16 + O 16 scattering to the lowest 2 + and 3 − excited states of O 16 have been measured at E lab = 250 , 350 , 480 , 704 and 1120 MeV and analyzed consistently in the distorted wave Born approximation (DWBA), using the semi-microscopic optical potentials and inelastic form factors given by the folding model, to reveal possible refractive structure of the nuclear rainbow that was identified earlier in the elastic O 16 + O 16 scattering channel at the same energies. Given the known transition strengths of the 2 1 + and 3 1 − states of O 16 well determined from the ( e , e ′ ) data, the DWBA description of the inelastic data over the whole angular range was possible only if the absorption in the exit channels is significantly increased (especially, for the O 16 + O 2 + ∗ 16 exit channel). Although the refractive pattern of the inelastic O 16 + O 16 scattering was found to be less pronounced compared to that observed in the elastic scattering channel, a clear remnant of the main rainbow maximum could still be seen in the inelastic cross section at E lab = 350 – 704 MeV .

Proton stripping induced by 13C at 50 MeV/nucleon on 12C, 40Ca and 58Ni

Abstract The ( 13 C, 12 B) reaction has been investigated at an incident energy of 50 MeV/u on 12 C, 40 Ca and 58 Ni using a magnetic spectrometer. The angular range measured covers the 0° beam direction. Angular distributions of discrete states as well as of structures in the continuum have been measured. They are compared with DWBA calculations. The absolute value of the cross section for the 12 C target is well reproduced, whereas for 40 Ca and 58 Ni discrepancies of a factor 10 are observed.

One-neutron transfer reaction and refractive effects in the 16O+16O system

One-neutron transfer data of the 16 O( 16 O, 17 O) 15 O reaction have been measured for the p1/2 ground state and p3/2 excited hole state in 15 O, at incident energies ranging from 250 to 1120 MeV. Some remnant of refraction (rainbow) pattern was observed for the ground state transition to 15 O1/2− , whereas for the neutron hole state 15 O ∗/2− at 6.176 MeV excitation energy the angular distributions show more or less an exponential fall-off. The data were analyzed using the full finiterange distorted wave Born approximation (DWBA). The DWBA description of the transfer data over the whole measured angular range was possible only, if the indirect term of the transition operator is properly included and the absorption in the exit channels is substantially increased, especially, for the 15 O ∗/2− channel. The energy dependence of the transfer cross sections has been consistently described with two choices for the real part of the optical potential: the folding potential and the squared Woods–Saxon potential. The obtained spectroscopic factors, S(1/2 − ) = 1.8 ± 0.3 and S(3/2 − ) = 4.0 ± 0.5, are energy independent. uf6d9 2002 Elsevier Science B.V. All rights reserved.

Nuclear-rainbow scattering and nucleus-nucleus potentials at short distances

The elastic scattering of strongly bound nuclei at energies of 10 to 70 MeV per nucleon shows the phenomenon of “rainbow scattering.” A nuclear rainbow appears because of deflection to negative angles. This process involves a strong overlap of nuclear densities, with values of up to twice the saturation density of nuclear matter. The 16O+16O system is studied with a high precision over a wide energy range from 7 to 70 MeV per nucleon in several laboratories. Primary Airy maxima and higher order Airy structures are observed. At all energies, excellent fits are obtained with deep potentials as deduced from the double-folding model involving a nucleon-nucleon interaction weakly dependent on the density. It is shown that Pauli blocking expected at low energies is strongly reduced if the local momenta are calculated self-consistently. Systematics confirms a refractive origin of large-angle scattering, at low energies inclusive. Thus, nuclear-rainbow scattering yields unique information about the properties of cold nuclear matter at higher densities.

Nuclear structure studies of bound and unbound states in drip-line nuclei

SummaryThe structure of the neutron-rich isotopes7He,10Li and11Be has been studied in detail using multi-nucleon transfer reactions. New results have been obtained for7He, where we have evidence for the observation of the first excited state, i.e. the 1/2--resonance, which is of interest for the spin-orbit splitting in these light neutron-rich nuclei. Reactions of distinct selectivity have been chosen to study the states of10Li, which are all unbound. The structure of the eight states found in these reactions is discussed, and the relevance for the decay of11Li resonances is shown. The isotopes10Be and11Be have been investigated to study the α-cluster structure and high-lying states. Nine states of the observed11Be-resonances form a molecu-lar rotational band. The multi-nucleon transfer mechanism has also been applied to study the unbound proton-rich isotope11N, the mirror nucleus of11Be. In this case the12C(14N,15C)11N-reaction has been used. Five resonances have been observed, and the lowest two can be identified as 1/2- -and 5/2+ -states.