A. S. Demyanova

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.

Rainbows in Nuclear Reactions and the Optical Potential

Nucleus-nucleus scattering and charge-exchange reactions are studied in a region where rainbow-like phenomena are seen. Optical potentials are found which give fits to the cross sections, but in spite of the rainbow-like phenomena and contrary to apparently accepted expectations, not determined unambiguously. Other possibilities of resolving the ambiguities are discussed.

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.

Scattering of 3He on 12C and the inelastic form factor

Abstract Measurements of inelastic scattering of 3He on 12C at EHe = 72 MeV with excitation of low lying 2+, 3−, 0+ states of the target are reported. The data were analyzed both by DWBA and coupled-channels approximation, the latter leading to only minor changes, and we argue that nuclear rainbow effects are present. It is possible to reproduce the main features of the 2+ and 3− inelastic angular distributions by means of the optical model potential previously selected for the reaction (3He, t) on 13,14C targets, only if the derivative excitation form factors are modified in the vicinity of the strong absorption radius. The fit is improved in detail and can be made nearly perfect if more flexible model-independent form factors are employed. An alternative potential is also discussed.

Observation of abnormally large radii of nuclei in excited states in the vicinity of neutron thresholds

Differential cross sections for inelastic scattering leading to the excitation of some nuclear states situated near neutron-emission thresholds were analyzed. With the aid of a modified diffraction model, abnormally large radii were found for the 1/21+ state of the 13C nucleus at 3.09 MeV, for the first levels of positive-parity rotational bands in the 9Be (1/2+ level at 1.68 MeV and 5/2+ level at 3.05 MeV) and 11Be (5/2+ level at 1.78 MeV and 3/2+ level at 3.41 MeV) nuclei, and for the 21+ state of the 14Be nucleus at 1.54 MeV and 11− state of the 12Be nucleus at 2.7 MeV. All of these states possess signatures typical of neutron halos.

α + 12C scattering at 110 MeV: Has exotic 7.65 MeV Hoyle’s state signatures “alpha-condensate” structure?

We present new measurements of the α + 12C elastic and inelastic (to the states 4.44, 7.65, and 9.64 MeV) scattering at Elab = 110 MeV in the wide angular range from ∼10° to 175°, which enable us to examine the condensate and cluster properties of the low-lying excited states in 12C. We present the diffraction-radius analysis of our data together with a considerable amount of the existing data. The magnitudes of the diffraction radii for the ground and the first excited (4.44 MeV) states are found to be equal, whereas they appear to be enhanced by ∼0.6 fm both for 7.65 and 9.64 MeV states. This result shows that the radius of the Hoyle’s 02+, 7.65 MeV state in 12C is by a factor of ∼1.2–1.3 larger than that of the ground state. It is demonstrated that the direct transfer mechanism of 8Be dominates at the largest angles in all four reactions reported here. The configuration corresponding to the transfer of 8Be in its ground state (Iπ = 0+) with L = 0 turns out to be the most important for the 7.65 MeV state of 12C. Evidence of existence of some features of α-condensed structure of the Hoyle’s 02+ state in 12C was obtained: its enhanced radius and large contribution of α-particle configuration with L = 0.

Study of rlastic and inelastic 11B +α scattering and search for cluster states of enlarged radius in 11B

The differential cross sections for elastic and inelastic 11B + α scattering were measured at the alpha-particle energy of 65 MeV, the inelastic-scattering processes leading to the excitation of known states of 11B up to excitation energies of about 14 MeV. Data on elastic scattering were analyzed together with those that were published earlier for lower energies. The cross sections for inelastic scattering were analyzed on the basis of the distorted-wave method. A modified diffractionmodel was used to determine the root-mean-square radii of excited states. The radii of states whose excitation energies were below about 7MeV were found to agree with radius of the ground state to within 0.1 to 0.15 fm. This result complieswith the traditional idea that the low-lying states of 11B have a shell structure. The possibility that these states belong to the predicted rotational bands, which, if any, are truncated to three states, cannot be ruled out either. The majority of the observed highly excited states are distributed among four rotational bands. The moments of inertia of these bands are close; for the band based on the 3/2− state at E* = 8.56 MeV, they are even higher than those of the Hoyle state in the 12C nucleus. The measured radii of states associated with these bands of 11B are larger than the ground-state radius by 0.7 to 1.0 fm and are also close to the radius of the Hoyle state. The results of the present study agree with the existing predictions that the cluster structure of the 11B nucleus is diverse at high excitation energies. The hypothesis that the 11B nucleus features a “giant” state of size commensurate with those in heavy nuclei was not confirmed.

Investigation of the nucleus-nucleus interaction at small distances in elastic scattering of 6li and the reaction (6Li, 6He) on carbon isotopes

Abstract The cross sections of elastic scattering of 6Li and of the charge-exchange reaction (6Li, 6He) on the nuclei 13C and 14C were measured at the projectile energy 93 MeV. A theoretical analysis of the reaction was carried out using microscopic DWBA with central and tensor components of the nucleon-nucleon forces and the decomposition of the reaction amplitude to near side and far side components. The far components were seen to dominate both the elastic scattering and the reaction for the angles above 30°, and a small shoulder in the differential cross section curves around 90° in elastic scattering and in 14C(6Li, 6He) 14N(3.95) may be interpreted as a rudimentary nuclear rainbow. The analysis of the scattering data lead to a new family of potentials for the systems 6Li + 12,13,14C. The reproduction of the differential cross sections for population of the 1+ states in the charge-exchange reaction at large angles called for a change of the form factors, compared to the theoretical ones, for radii which were considerably smaller than the strong absorption radius. It is possible that to reproduce the (6Li, 6He) reaction data, a 20% difference between the imaginary potentials of 6He and 6Li is needed.

Neutron Halo in the Exotic First Excited State of 9Be

Differential cross sections for elastic and inelastic 9Be + α scattering (the inelastic scattering leading to the 1.68- and 2.43-MeV states) were measured at the energies of 40 and 90 MeV. The radii of the excited states in question were determined on the basis of a modified diffraction model. The root-mean-square radius of the level at 1.68 MeV proved to be approximately 1 fm larger than the radii of both neighboring states. The reason is that, for this level, there is a neutron halo whose properties are similar to the properties of the known halo in the 11Be nucleus. This result is the first observation of a halo in an unbound state lying above the neutronemission threshold.

Refractive effects and Airy structure in inelastic

Inelastic