Investigation of the isoscalar response ofMg24toLi6scattering

Abstract

Background: 24 Mg is a strongly deformed nucleus in the ground state. Deformation effects can be observed in the structure of the isoscalar giant monopole and quadrupole resonances. 24 Mg is also a nucleus that is well known to present different types of cluster-oscillation modes. Both giant resonances and cluster states are strongly populated by isoscalar transitions. Purpose: To extract the E 0, E 1, and E 2 transition strengths via 6 Li scattering. The 6 Li probe is a powerful tool for investigating the isoscalar nuclear response with a very favorable ratio of resonance-to-continuum background. Method: Double-differential cross sections of 6 Li inelastic scattering, at the beam energy of 100 MeV/u, were measured in the excitation-energy range 10-40 MeV and scattering angles 0−3 • . A multipole-decomposition analysis was performed for extracting the isoscalar E 0, E 1, and E 2 strength distributions. Results: The extracted multipole strengths were compared with predictions from consistent quasiparticle random phase approximation calculations. The theoretical predictions are in fair agreement with the experimental data. The E 0 strength was also compared with results from antisymmetrized molecular dynamics calculations found in the literature. A few peaks in the experimental data might be associated with clustering in 24 Mg. Conclusions: Ground-state deformation effects were observed in the isoscalar giant monopole resonance (ISGMR) and isoscalar giant quadrupole resonance (ISGQR) distributions. The ISGMR strength is split in two peaks around 19 and 28 MeV. The ISGQR exhibits a pronounced peak at 20 MeV with a broadening at the low-energy region, similar to predictions from microscopic calculations. Signatures of excitation of cluster states were observed in the E 0 response. Further studies including particle-decay measurements will be required to confirm the nature of the observed peaks.

Isoscalar giant monopole resonance in $^{24}$Mg and $^{28}$Si: Effect of coupling between the isoscalar monopole and quadrupole strength

“…In particular, the RCNP experiments [12,14] suggest the highest IS0 structures at 16 − 20 MeV and a two times lower peak at 13 − 16 MeV. A similar structure was observed in the recent ( 6 Li, 6 Li ′ ) experiment [17]. Instead, the TAMU and iThemba LABS data (bottom panel of Fig.…”

“…The present iThemba LABS data are shown as black filled circles. Also shown are the (α, α ′ ) [12,14] and ( 6 Li, 6 Li ′ ) data [17] from the RCNP shown as blue and red histograms, respectively (top panel). The bottom panel displays results from TAMU [18] (magenta histogram) and a different measurement at RCNP [15] shown by dark cyan histogram.…”

“…More recent (α, α ′ ) experiments were performed at the Research Center for Nuclear Physics (RCNP) for 24 Mg [12,14,15] and 28 Si [16]. In 2021, the results of an RCNP ( 6 Li, 6 Li ′ ) experiment on IS0 strength in 24 Mg were published [17]. The IS0/IS2 coupling was mentioned in Refs.…”

“…The IS0/IS2 coupling was mentioned in Refs. [12,17] in order to explain the existence of the IS0 structure located around 16 − 19 MeV excitation in 24 Mg. The existence of a prominent IS0 peak at about 18 MeV in oblate 28 Si was noted but not yet explained [16].…”

“…However, in the study [21], the narrow IS0 peaks in 24 Mg and 28 Si were not specifically discussed. Furthermore, one can dispute whether the low-energy narrow IS0 peak in 24 Mg has been correctly assigned (and used in the QRPA analysis) in the RCNP studies [12,14,17] (see discussion in Sect.…”