Th. Wilpert

Nuclear rainbow structures in the elastic scattering of 16O on 16O at EL=350 Me

Abstract The elastic scattering of 16O on 16O has been measured at 22MeV/u in a large angular range up to θcm=61° with high accuracy. Besides the Fraunhofer diffractive patterns at forward angles a clear oscillatory structure is observed at large angles. It is shown in a semi-classical analysis that this structure is due to a rainbow interference of two refractive amplitudes (the second Airy maximum is identified). These data show a nuclear rainbow structure for the first time in heavy-ion scattering (A>6) with unambiguous clarity.

Refractive scattering and the nuclear rainbow in the interaction of12, 13C with12C at 20MeV/N

The elastic and inelastic scattering and the neutron transfer have been measured for the systems12C +12C and13C +12C at 20MeV/N up to θcm= 60° with theQ3D -spectrometer. The angular distributions of the elastic scattering show an enhanced cross section at angles larger than 40°. It can be identified as refractive scattering with the clear signature of a nuclear rainbow.L-cut-off calculations show that these contributions come fromL-values which are significantly lower than the grazingL-value. The deflection function has a broad minimum in thisL-range which is typical for rainbow scattering. TheS-matrix is decomposed by a phenomenological parametrization into a refractive and a diffractive part. The interference of these amplitudes plays an important role in the rainbow enhancement. The spatial localization of the refractive scattering is deduced from the turning points of the corresponding trajectories; a localization between 2.5 fm and 4 fm is found. Semi-classical calculations with complex trajectories in the single-turning-point approximation show good agreement with the quantummechanical calculations. Refractive contributions are not observed in the inelastic scattering. This can be explained by reducing the strength of the conventional collective form factor in the internal region. In contrast to this the enhancement at large angles is seen in the one-neutron transfer channels where the refractive scattering is dominant. This is the first observation of such contributions to heavy-ion transfer reactions.

Spectroscopy of 10He

Abstract The mass of 10 He has been measured with the double charge exchange reaction 10 Be( 14 C, 14 O) 10 He at E Lab = 334.4 MeV and a mass excess M.E. = 48.81 (7) MeV is obtained. It follows that 10 He is particle unstable against 2 n - emission by S 2n = −1.07(7) MeV . Two excited states are observed: a broad resonance at an excitation energy of E x = 3.24(20) MeV , and a strong resonance at E x = 6.80(7) MeV .

Stud of weakly bound and unbound states of exotic nuclei with binary reactions

Abstract Binary reactions using neutron-rich beams (and targets) give the best approach to study the level structure of exotic nuclei. Systematic cross section dependencies of multi-step transfer reactions are discussed. Some rections, for example the proton-neutron exchange ( 12 C, 12 N) and ( 13 C, 13 N) , have distinct selectivity for the population of unnatural or natural parity states, respectively. This selectivity has been applied to new spectroscopic studies of 10 Li using the 10 Be( 12 C, 12 N) and 9 Be)(P 13 C, 12 N) reactions. The lowest resonance of 10 Li observed at 0.24(6) MeV above the neutron threshold. The results are discussed together with other available data.

Mass spectroscopy of13Be

The mass of13Be has been measured with the reaction13C(14C,14O)13Be at ELab=337 MeV. A Q-value of Q0=−37.02(5) MeV was obtained and the mass excess is M.E.=35.16(5) MeV. If the observed line corresponds to the ground state,13 Be is particle unstable with respect to the oneneutron emission by 2.01 MeV. The observed line width of 0.3(2) MeV supports an assignment ofJπ=5/2+ or 1/2−, but excludesJπ=1/2+. An excited state is seen at 3.12(7) MeV; there are indications of a second excited state at 6.5(2) MeV.

Spectroscopy of 13B, 14B, 15B and 16B using multi-nucleon transfer reactions

Abstract: New information has been obtained on excited states of the neutron-rich boron isotopes 14B, 15B and 16B, using the reactions 12C(14C,12N)14B, 13C(14C,12N)15B and 14C(14C,12N)16B at about 24 MeV/A. The mass excess of 16B has been measured for the first time, it is 37.08(6) MeV. This means that 16B is unbound by only 0.04(6) MeV. Furthermore, the nucleus 13B has been investigated with the four reactions 16O(14C,17F), 12C(14C,13N), 12C(13C,12N) and 12C(15N,14O). Choosing different target-projectile combinations, it was possible to populate states with different selectivity. New states are observed in 13B at excitation energies above the threshold for two-neutron decay.

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.

Spectroscopy of excited states of11Li

The10Be(14C,13N)11 Lireaction and the14C(14C,17F)11 Lireaction have been used to study the levels of11Li. Three excited states have been found, in both reactions, at excitation energies of 2.47(7) MeV, 4.85(7) MeVand 6.22(8) MeV

Study of light neutron-rich nuclei with 14C-induced reactions

Abstract The 14C-beam has been used at HMI to study light neutron-rich nuclei with multi-nucleon transfer reactions. Spectroscopic results about the T=3 nuclei 10He, 14Be and 16B have been obtained, but also 11Li, 7He and the 3n-system have been investigated.

Refractive scattering and reactions, comparison of two systems:16O+16O and20Ne+12C

Elastic, inelastic scattering as well as one-neutron transfer channels have been measured over a wide angular range for systems16O+16O at the incident energy of 350 MeV and20Ne+12C at 390 MeV, respectively, using the Q3D magnetic spectrometer. In both cases differential cross sections have been measured down to about 50 nb/sr (or dσ/dσR≤10−4) at large angles. For the16O+16O system refractive contributions are found at the level of these cross sections, whereas in the20Ne+12C case a steeper decrease of the differential cross section with the angle is observed and the refractive contribution can not be determined. The elastic scattering data have been analyzed using standard Woods-Saxon potentials and potentials calculated in different versions of the double-folding model. Some properties of these potentials are tested in the calculations for inelastic scattering and one-neutron transfer within the DWBA. With the refractive pattern observed for the16O+16O system, the scattering and transfer data are found to be sensitive to the interaction potential at small internuclear distances down to about 2.5 fm.