Publisher’s Note: Measurement of the Isoscalar Monopole Rsponse in the Neutron-Rich NucleusNi68[Phys. Rev. Lett. 113, 032504 (2014)]

Abstract

The isoscalar monopole response has been measured in the unstable nucleus 68 Ni using inelastic alpha scattering at 50A MeV in inverse kinematics with the active target MAYA at GANIL. The isoscalar giant monopole resonance (ISGMR) centroid was determined to be 21.1 AE 1.9 MeV and indications for a soft monopole mode are provided for the first time at 12.9 AE 1.0 MeV. Analysis of the corresponding angular distributions using distorted-wave-born approximation with random-phase approximation transition densities indicates that the L ¼ 0 multipolarity dominates the cross section for the ISGMR and significantly contributes to the low-energy mode. The L ¼ 0 part of this low-energy mode, the soft monopole mode, is dominated by neutron excitations. This demonstrates the relevance of inelastic alpha scattering in inverse kinematics in order to probe both the ISGMR and isoscalar soft modes in neutron-rich nuclei.

Active targets for the study of nuclei far from stability

“…Due to the negative Q -value, and in order to have predominantly a direct reaction mechanism, energies of 50 MeV/n or higher are necessary. Two Ni isotopes have been studied with the Maya detector at GANIL: 56 Ni and 68 Ni [49,50]. We will illustrate the results for 68 Ni, a neutron rich isotope.…”

“…The soft monopole resonance can be understood as a neutron compressional mode, without participation of the protons, as shown in Fig. 12(a) from [50,51]. The 21 MeV resonance is described by an oscillation of protons and neutrons in phase, this is the extensively studied monopole compressional mode, important for its relation to the nuclear incompressibility.…”

The compression-mode giant resonances and nuclear incompressibility

“…In two measurements, performed also at GANIL, the aforementioned problems associated with using (α, α ) for ISGMR using an AT-TPC device were largely overcome [197,193,198]. Helium gas was used at a pressure of 500 mbar in MAYA, with 5% of CF 4 as the quencher.…”

“…Helium gas was used at a pressure of 500 mbar in MAYA, with 5% of CF 4 as the quencher. Two different radioactive ion beams, 56 Ni (∼2×10 4 pps) and 68 Ni (∼4×10 4 pps), both at 50 MeV/nucleon incident energy, were employed, with data taken on 68 Ni also for (d, d ) to obtain a direct comparison between the two probes; the statistics in the (d, d ) data was much lower than in (α, α ) because of the lower cross section for (d, d ), as also the experimental conditions of pressure and high voltage employed in the two experiments [197,193]. In all cases, a number of narrow peaks are observed in the inelastic scattering spectra sitting atop, so to speak, a large background.…”

MICROMEGAS calibration for ACTAR TPC

“…It was followed by the MAYA active target at GANIL [3][4][5] and the CENBG TPC [6,7] used for decay studies. In order to gain in sensitivity and precision on the reconstruction of trajectories, the next generation active target ACTAR TPC is now being developed at GANIL.…”