A. A. Ogloblin

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.

Observation of 10He

Abstract The reactions 11 Li + CD 2 → 10 He + X and 11 Li + C → 10 He + X at a beam energy of 61A MeV have been studied by measuring the triple coincidence of 8He and two neutrons. Experimental data show a peak that can be explained as a resonance 10He, which is unbound by 1.2±0.3 MeV and its width is less than 1.2 MeV. Theinvariant mass spectra of 8He+n show a peak that is consistent with the decay 10 He → 8 He + n + n .

Scattering of radioactive nuclei 6He and 3H by protons: Effects of neutron skin and halo in 6He, 8He, and 11Li

In an experimental study of 6He+p and 3H+p collisions at ∼70 A MeV, the elastic scattering angular distributions were measured and the known excited state 6He1.8∗ was observed. Comparative analysis of existing experimental data on proton elastic scattering by 4He, 6He, 6Li, 8He, 9Li, and 11Li was performed. Effects of valence neutrons were investigated using the eikonal approach. A difference between 11Li and 6,8He was found.

Spectroscopy of 12Be and 13Be using a 12Be radioactive beam

Abstract We have studied 12 Be + p elastic and inelastic scattering and observed new levels of 12 Be at E 12 Be ∗ = 8.6, 10 and ∼ 14 MeV in the vicinity of He-emission thresholds, which can be candidates for states having an exotic cluster structure with He-like subsystems. Some new states were tentatively assigned to 13 Be in studies of the d( 12 Be, p) reaction.

Experimental study of 8He + p elastic and inelastic scattering

Abstract An experimental study of 8He + p elastic scattering and a search for 8He∗ as observed in two independent experimental methods. The obtained parameters of the excited state are E 8 He ∗ = 3.57±0.12 MeV , Γ =0.5±0.35 MeV, Γ 4 He+4n /Γ 6 He+n+n ⩽ 5% . Angular distributions for elastic and inelastic scattering are measured. The inelastic angular distribution is consistent with Jπ = 2+ for 8He3.55∗.

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.

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.

Nuclear structure studies of very neutron-rich isotopes of 7–10He, 9–11Li and 12–14Be via two-body reactions

A considerable number of experiments is nowadays devoted to the study of exotic nuclei, mainly by using secondary beams produced by high energy fragmentation of heavier nuclei. In these eases mainly the properties of the bound nuclei (usually ground states) are accessible. In the studies persued at the HMI various two-body reactions populating bound and unbound states have been studied using beams of 13C and 14C of typically 24 MeV/nueleon and neutron-rich targets [ 1-3]. The energy spectrum of excited states (resonances) in exotic nuclei is thus obtained and the width of resonances gives an indirect information for the assignment of quantum numbers. We have focussed our attention to the light neutron rich isotopes of He, Li, Be and B. Some of the isotopes for which we have obtained results are marked in Fig. 1. The excitation energy spectra of these nuclei will reflect the particular deviations from the standard shell model which are often discussed in neutron rich nuclei [4-6].

Production cross-sections of light neutron-rich nuclei from 40Ar fragmentation at about 1 GeV/nucleon

Abstract Using a primary beam of 40 Ar at ∼1A GeV impinging on a Be target, the production cross-sections of light neutron-rich fragments from projectile fragmentation were measured at the projectile-fragment separator FRS at GSI. The experimental cross-sections were obtained for isotopes of the elements B to F both close to stability and near the neutron drip line. These data are compared to the results of the empirical parametrization EPAX. We also compare the results to those measured previously at LBL. As an additional result, the particle instability of 26 O has been confirmed.