Search

The 12C(18O,16O)14C reaction at 84 MeV incident energy has been explored up to high excitation energy of the residual nucleus thanks to the use of the MAGNEX spectrometer to detect the ejectiles. In the region above the two-neutron separation energy, a resonance at 16.9 MeV has been observed. Continuum quasi-particle random phase approximation calculations of the response function, corresponding to the transfer of a neutron pair to the 12C nucleus, have been performed to investigate the possible presence of the Giant Pairing Vibration in that energy region. [ABSTRACT FROM AUTHOR]

The 12C(18O, 16O) 14C and C(18O, 17O) 14C reactions were studied at INFN-LNS laboratory in Catania. The experiments were performed using an 18O Tandem beam at 84 MeV incident energy. Charged ejectiles produced in the reactions were momentum analyzed and identified by the MAGNEX spectrometer. Q-value spectra were extracted with a remarkable energy resolution (FWHM ~ 150 keV) and several known bound and resonant states were identified. In particular, states with relevant 1p-3h configuration with respect to the 16O core are mainly populated by the reaction (18O, 17O) while states with known 2p-4h configuration are excited by the (18O, 16O) one. Exact Finite Range Coupled Reaction Channel calculations based on a parameter free double-folding optical potential were performed to reproduce the measured absolute cross-section angular distributions. The (18O, 16O) is found to be an important probe to study pair configurations in nuclear states. [ABSTRACT FROM AUTHOR]

A study of the continuum of Be populated by the 9Be(18O, 16O) 11Be reaction at 84 MeV incident energy has been performed. The ejectiles have been momentum analysed at forward angles by the MAGNEX magnetic spectrometer and 11Be energy spectra have been obtained up to about 13 MeV. The scattering of two neutrons independently removed from the projectile as it passes the target nucleus has been described by means of an optical potential with a semiclassical approximation for the relative motion. [ABSTRACT FROM AUTHOR]

The 12C(18O,16O)14C and 12,13C(18O,17O)13,14C reactions are studied at 84 MeV. Mass distributions and energy spectra of the ejectiles are measured, indicating the selectivity of these reactions to populate two- and one-neutron configurations in the states of the residual nucleus, respectively. The measured absolute cross-section angular distributions are analyzed by exact finite range coupled reaction channel calculations based on a parameter free double-folding optical potential. The form factors for the (18O,16O) reaction are extracted within an extreme cluster and independent particles scheme with shell-model-derived coupling strengths. The results show that the measured cross sections are accurately described for the first time without the need for any arbitrary scaling factor. The (18O,16O) reaction is thus found to be a powerful tool for quantitative spectroscopic studies of pair configurations in nuclear states. [ABSTRACT FROM AUTHOR]

The N = 8 neutron-rich nucleus 13B has been investigated via the (18O,16O) two neutron transfer reaction at 85 MeV. Several excited states are populated in the final nucleus. A comparison with the 12C(18O,16O)14C two neutron transfer reaction at the same incident energy seems to confirm the rapid shell evolution recently observed in the N = 8 systems. [ABSTRACT FROM AUTHOR]

Experimental signatures of the dynamical correlations of a core with a single-particle neutron have been found in light neutron-rich nuclei investigated via the ( 7Li, 7Be) charge-exchange reactions at around 8MeV/u. Of particular astrophysical relevance are low-lying narrow resonances ( Γ ∼ 200keV FWHM) BSEC (Bound States Embedded in the Continuum). Because of their long lifetime BSEC states are likely to effect the capture rates in any scenario for nucleosynthesis in neutron-rich environment. They have been observed in the continuum of 11Be and 15C nuclei. A microscopic nuclear structure model based on QRPA theory, which takes into account Dynamical Core Polarisation (DCP) correlations, gives a suitable description of these resonances as well as single-particle states of the studied systems. In this context, high-energy narrow structures populated in nuclei having an integer number of α-particles plus three neutrons are good BSEC candidates and can be systematically investigated. [ABSTRACT FROM AUTHOR]

Recently a quantitative description of the two-neutron transfer reaction 12C(18O, 16O)14C was performed and the measured cross sections were successfully reproduced [M. Cavallaro et al., Phys. Rev. C 88, 054601 (2013)]. This task was accomplished by combining nuclear structure calculations of spectroscopic amplitudes and a full quantum description of the reaction mechanism. Verification of such a theoretical approach to other heavy nuclear systems is mandatory in order to use (18O, 16O) reactions to assess pair configurations in nuclear states. In this work we apply this methodology to the 16O(18O, 16O)18O reaction at 84 MeV. Experimental angular distributions for the two-neutron transfer to the ground state and 2+1 state of 18O were obtained using the MAGNEX spectrometer at INFN-LNS. The roles of one- and two-step processes are analyzed under the exact finite range coupled reaction channel and the second order distorted wave Born approximation. We conclude that the one-step transfer mechanism is dominant in this system. [ABSTRACT FROM AUTHOR]

Heavy-ion induced two-neutron transfer reactions (18O,16O) at 84 MeV were studied on several targets up to high excitation energy of the residual nucleus thanks to the use of the MAGNEX magnetic spectrometer to detect the ejectiles. The obtained results indicate of the important role played by the nuclear paring. [ABSTRACT FROM AUTHOR]

Background: Recently, a systematic exploration of two-neutron transfer induced by the (18O,16O) reaction on different targets has been performed. The high-resolution data have been collected at the MAGNEX magnetic spectrometer of the INFN-LNS Laboratory in Catania and analyzed with the coupled reaction channel (CRC) approach. The simultaneous and sequential transfers of the two neutrons have been considered under the same theoretical framework without the need for adjustable factors in the calculations. Purpose: A detailed analysis of the one-neutron transfer cross sections is important to study the sequential two-neutron transfer. Here, we examine the (18O,17O) reaction on 16O,28Si, and 64Ni targets. These even-even nuclei allow for investigation of one-neutron transfer in distinct nuclear shell spaces. Method: The MAGNEX spectrometer was used to measure mass spectra of ejectiles and extract differential cross sections of one-neutron transfer to low-lying states. We adopted the same CRC formalism used in the sequential two-neutron transfer, including relevant channels and using spectroscopic amplitudes obtained from shell-model calculations. We also compare with the one-step distorted-wave Born approximation (DWBA). Results: For the 18O+16O and the 18O+28O systems, we used two interactions in the shell model. The experimental angular distributions are reasonably well reproduced by the CRC calculations. In the 18O+64Ni system, we considered only one interaction, and the theoretical curve describes the shape and order of magnitude observed in the experimental data. Conclusions: Comparisons between experimental DWBA and CRC angle-integrated cross sections suggest that excitations before or after the transfer of a neutron are relevant in the 18O+16O and 18O+64Ni systems. [ABSTRACT FROM AUTHOR]

Background: In our recent work [M. J. Ermamatov et al., Phys. Rev. C 94, 024610 (2016)], the two-neutron transfer induced by the (18O,16O) reaction was studied for 16O nucleus. Theoretical analysis of the low-lying states of 18O indicates that the transfer to the ground state proceeds predominantly through simultaneous transfer of the two-neutron system. Purpose: In this work, we extend our previous theoretical analysis towards high-lying states of the 18O nucleus. In order to achieve a comprehensive picture, we revisit the experimental data for the 16O(t,p)18O reaction at 15 MeV bombarding energy. We also include new experimental cross sections for the high-lying states of the 18O residual nucleus, populated in the 16O(18O,16O)18O reaction at 84 MeV. Method: The same spectroscopic parameters of the target nucleus were used as input in the coupled channel calculations for the transfer induced by triton and 18O projectiles. Simultaneous two-neutron transfer is calculated within the coupled reaction channel approach, using the extreme cluster and independent coordinate models. The sequential process is calculated within the distorted-wave Born approximation. Results: Theoretical calculations reproduce the 16O(t,p)18O data well, leading to natural parity states in the 18O nucleus without the need of adjustable parameters. The same methods are applied to the 16O(18O,16O)18O data and a good agreement is observed. Conclusions: Detailed analyses show the importance of a simultaneous mechanism for the two-neutron transfer reactions. In transferring two neutrons, the pairing correlation plays an important role. [ABSTRACT FROM AUTHOR]

Recently, various two-neutron transfer studies using the (18O,16O) reaction were performed with a large success. This was achieved because of a combined use of the microscopic quantum description of the reaction mechanism and of the nuclear structure. In the present work we use this methodology to study the two-neutron transfer reaction of the 18O+64Ni system at 84 MeV incident energy, to the ground and first 2+ excited state of the residual 66Ni nucleus. All the experimental data were measured by the large acceptance MAGNEX spectrometer at the Instituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (Italy). We have performed exact finite range cross section calculations using the coupled channel Born approximation (CCBA) and coupled reaction channel (CRC) method for the sequential and direct two-neutron transfers, respectively. Moreover, this is the first time that the formalism of the microscopic interaction boson model (IBM-2) was applied to a two-neutron transfer reaction. From our results we conclude that for two-neutron transfer to the ground state of 66Ni, the direct transfer is the dominant reaction mechanism, whereas for the transfer to the first excited state of 66Ni, the sequential process dominates. A competition between long-range and short-range correlations is discussed, in particular, how the use of two different models (Shell model and IBM's) help to disentangle long- and short-range correlations. [ABSTRACT FROM AUTHOR]

The neutron decay of the resonant states of light neutron-rich nuclei is an important and poorly explored property, useful to extract valuable nuclear structure information. In the present paper the neutron decay of the 15C resonances populated via the two-neutron transfer reaction 13C(18O,16On) at 84-MeV incident energy is reported for the first time using an innovative technique which couples the MAGNEX magnetic spectrometer and the EDEN neutron detector array. Experimental data show that the resonances below the one-neutron emission threshold decay to the 14C ground state via one-neutron emission with an almost 100% total branching ratio, whereas the recently observed 15C giant pairing vibration at 13.7 MeV mainly decays via two-neutron emission. [ABSTRACT FROM AUTHOR]