Search

The ability of a recently developed square-integrable discrete basis to represent the properties of the continuum of a two-body system is investigated. The basis is obtained performing a simple analytic local scale transformation to the harmonic oscillator basis. Scattering phase-shifts and the electric transition probabilities B(E1) and B(E2) have been evaluated for several potentials using the proposed basis. Both quantities are found to be in excellent agreement with the exact values calculated from the true scattering states. The basis has been applied to describe the projectile continuum in the 6He scattering by 12C and 208Pb targets at 240 MeV/nucleon and the 11Be scattering by 12C at 67 MeV/nucleon. The calculated breakup differential cross sections are found to be in very good agreement with the available experimental data for these reactions.

A powerful method of investigating proton-unbound nuclear states by tracking their decay products in flight is discussed in detail. To verify the method, four known levels in 15F, 16Ne, and 19Na were investigated by measuring the angular correlations between protons and the respective heavy-ion fragments stemming from the precursor decays in flight. The parent nuclei of interest were produced in nuclear reactions of one-neutron removal from 17Ne and 20Mg projectiles at energies of 410-450 A MeV. The trajectories of the respective decay products, 14O+p+p and 18Ne+p+p, were measured by applying a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of the fragments, which provided information on energies and widths of the parent states. In addition for reproducing properties of known states, evidence for hitherto unknown excited states in 15F and 16Ne was found. This tracking technique has an advantage in studies of exotic nuclei beyond the proton drip line measuring the resonance energies and widths with a high precision although by using low-intensity beams and very thick targets.

Two high-lying states in 15F and 16Ne, unbound with respect to one-proton (1p) and two-proton (2p) emissions, have been observed in the fragmentation of 17Ne at intermediate energies. They undergo mainly sequential emissions of protons via intermediate states in 14O and 15F and have decay energies of 7.8(2) and 7.6(2) MeV, respectively. The widths of the newly observed states in 15F and 16Ne are much smaller than the Wigner limits for single-particle configurations, of 0.4(4) and 0.8(+8-4) MeV, respectively. In addition, narrow widths of 0.2(2) MeV are derived for two other high-lying states in 15F with Qp of 4.9 and 6.4 MeV, which match features of the recently predicted narrow odd-parity 15F states with two valence protons in the sd shell. All energies and widths have been obtained by analyzing angular correlations of the decay products, p-p-14O and p-p-13N, whose trajectories have been measured by a tracking technique with silicon microstrip detectors.

The development of a continuum-bin scheme of discretization for three-body projectiles is necessary for studies of reactions of Borromean nuclei such as He6 within the continuum-discretized coupled-channels approach. Such a procedure, for constructing bin states on selected continuum energy intervals, is formulated and applied for the first time to reactions of a three-body projectile. The continuum representation uses the eigenchannel expansion of the three-body S matrix. The method is applied to the challenging case of the 6He+208Pb reaction at 22 MeV, where an accurate treatment of both the Coulomb and the nuclear interactions with the target is necessary.

A new method for continuum discretization in continuum-discretized coupled-channels calculations is proposed. The method is based on an analytic local-scale transformation of the harmonic-oscillator wave functions proposed for other purposes in a recent work. The new approach is compared with the standard method of continuum discretization in terms of energy bins for the reactions d+58Ni at 80 MeV, 6Li+40Ca at 156 MeV, and 6He+208Pb at 22 MeV and 240 MeV/nucleon. In all cases very good agreement between both approaches is found.

The scattering of a weakly bound three-body system by a target is discussed. A transformed harmonic oscillator basis is used to provide an appropriate discrete and finite basis for treating the continuum part of the spectrum of the projectile. The continuum-discretized coupled-channels framework is used for the scattering calculations. The formalism is applied to different reactions, 6He+12C at 229.8 MeV, 6He+64Zn at 10 and 13.6 MeV, and 6He+208Pb at 22 MeV, induced by the Borromean nucleus 6He. Both the Coulomb and nuclear interactions with a target are taken into account.

Proton-proton correlations were observed for the two-proton decays of the ground states of 19Mg and 16Ne. The trajectories of the respective decay products, 17Ne+p+p and 14O+p+p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.