L. V. Chulkov

Invariant-mass spectroscopy of 10Li and 11Li

Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb targets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing different reaction mechanisms. Invariant-mass spectroscopy for Li-11 and Li-10 is performed. The E1 strength distribution, deduced from electromagnetic excitation of Li-11 up to an excitation energy of 4 MeV comprises similar to 8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li-10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carrying 26(10)% of the strength and likely to be associated with an s-wave neutron decay. A strong di-neutron correlation in Li-11 can be discarded. Calculations in a quasi-particle RPA approach are compared with the experimental results for Li-10 and Li-11

Measurements of interaction cross sections for light neutron-rich nuclei at relativistic energies and determination of effective matter radii

Abstract We measured the interaction cross sections ( σ I ) of 10,11B, 12–20C, 14–23N, 16–24O and 18–26F on carbon targets at energies of around 950 A MeV. We then deduced the effective matter radii of the nuclei by a Glauber-model analysis. Based on the assumption of a core plus a valence neutron structure, we applied a Glauber-model analysis for a few-body system adapted for nuclei with an odd neutron number. We also deduced the effective nucleus-matter densities as well as some spectroscopic information for selected nuclei. Evidence for a one-neutron halo structure was found for 22N, 23O and 24F, as well as 19C.

Democratic decay of 6Be states

Abstract Decays of the 6 Be(0 + ) and 6 Be ∗ (2 + ) states into α + p + p are investigated by measuring spectra of each decay product, as well as in a kinematically complete experiment. Data on the decay characteristics are obtained. It has been found that the decays of 6 Be(0 + ) and 6 Be ∗ (2 + ) are reduced to exotic processes characterized by specific correlations of the α + p + p particles.

Interaction cross sections and matter radii of A = 20 isobars

Abstract High-energy interaction cross sections of A = 20 nuclei (20N, 20O, 20F, 20Ne, 20Na, 20Mg) on carbon were measured with accuracies of ≈ 1%. The nuclear matter r.m.s. radii derived from the measured cross sections show an irregular dependence on isospin projection. The largest difference in radii, which amounts to approximately 0.2 fm, has been obtained for the mirror nuclei 20O and 20Mg. The influence of nuclear deformation and binding energy on the radii is discussed. By evaluating the difference in r.m.s. radii of neutron and proton distributions, evidence has been found for the existence of a proton skin for 20Mg and of a neutron skin for 20N.

Nuclear radii of 17,19B and 14Be

Abstract The interaction cross sections ( σ I ) of light radioactive nuclei close to the neutron drip line ( 17,19 B, 14 Be) have been measured at around 800 A MeV. The effective root-mean-square (r.m.s.) matter radii of these nuclei have been deduced from σ I by two different methods, a Glauber-type calculation based on the optical limit approximation and a few-body reaction model. The deduced radii from both approaches agree with each other within experimental uncertainty. The r.m.s. radii of 17 B (2.99±0.09 fm) and of 14 Be (3.10±0.15 fm) in this work are consistent with the previously determined values, and have a higher accuracy. The r.m.s. radius of 19 B (3.11±0.13 fm) was newly determined. Assuming a “core plus 2n” structure in 17 B and 14 Be, the mixing of ν (2 s 1/2 ) and ν (1 d 5/2 ) was studied and the s -wave spectroscopic factor is found to be 36±19% and 47±25%, respectively. A valence radius analysis suggests a “core plus 4n” structure in 19 B.

Nuclear radii of Na and Mg isotopes

Abstract The effective root-mean-square (rms) matter radii of ANa (A = 20–23, 25–32) and AMg (A = 20, 22, 23, 27, 29–32) have been deduced from the measured interaction cross sections using a Glauber-type calculation. It was found that the increase of rms matter radii in Na isotopes is primarily a consequence of the increase of rms neutron radii. A correlation between the radii, corrected for quadrupole deformation, and the Fermi-energy difference was observed for both Na and Mg isotopes. This correlation can be explained by a model that assumes the valence nucleons are responsible for the changes in nuclear radii. The presence of a neutron skin is suggested for neutron-rich Na and Mg isotopes. An application to the nuclear equation of state (EOS) is discussed.

Measurements of the interaction cross sections for Ar and Cl isotopes

We have measured the interaction cross sections (σI) of 31–40Ar and 31–37Cl on carbon targets at energies of around 950 A MeV. The effective matter radii for these nuclei were deduced by a Glauber-model analysis. Combining our matter radii with measured charge radii for Ar isotopes, we could deduce the proton-skin thicknesses for the 32–40Ar isotopes, which were found to increase monotonically with decreasing neutron number. The larger radius of the proton drip-line nucleus 31Ar suggests an anomalous structure for this nucleus. In addition, using NaI(Tl) arrays surrounding the carbon target, we measured γ-rays emitted from excited states in these isotopes. In this way we could deduce the upper limits for the inelastic cross sections (σinela) on carbon targets at energies of around 950 A MeV.

8He-6He: a comparative study of nuclear fragmentation reactions

Dissociation of 227 MeV/u He-8 in a carbon target has been studied in kinematically complete experiments. The data include the relative energy spectrum, angular distributions in the neutron knock-out channel (He-6 + n) as well as diffractive dissociation and inelastic scattering into the (He-6 + 2n) channel. The data are compared with corresponding results from the well-known halo nucleus He-6. In both cases it is found that neutron knock-out is the: dominating reaction channel. The relative energy spectrum (He-6 + n) shows a structure, which is interpreted as being due to the I-pi = 3/2(-) resonance in the He-7 ground state with about equal contribution from its I-pi = 1/2(-) spin-orbit partner. The He-7 resonance shows a spin alignment similar to that observed in He-5, but with a smaller anisotropy indicating that the structure of the He-8 ground state is more complicated than that of He-6. The data in the (He-6 + 2n) channel were used to identify resonances in the excitation energy spectrum of He-8. If the spectrum is interpreted as two overlapping resonances, the spin-parity assignment for these is found to be 2(+) and 1(-), respectively.

Searching for the 5H resonance in the t+n+n system

19 pages, 7 figures, 2 tables, 2 appendices.-- PACS nrs.: 27.10.+h; 25.60.Gc.-- Printed version published Jul 28, 2003.

Invariant mass spectrum and alpha-n correlation function studied in the fragmentation of He-6 on a carbon target

Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (alpha+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(pi) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance