Reaction dynamics and nuclear structure of moderately neutron-rich Ne isotopes by heavy-ion reactions

The heavy-ion reaction ${}^{22}$Ne+${}^{208}$Pb at 128 MeV beam energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories. Elastic, inelastic, and one-nucleon transfer differential cross sections are measured and global agreement is obtained with semiclassical and distorted-wave Born approximation (DWBA) calculations. In particular, the angular distribution of the 2${}^{+}$ state of ${}^{22}$Ne is analyzed by DWBA and a similar calculation is performed for the unstable ${}^{24}$Ne nucleus, using existing data from the reaction ${}^{24}$Ne+${}^{208}$Pb at 182 MeV (measured at SPIRAL with the VAMOS-EXOGAM setup). In both cases the DWBA model gives a good reproduction of the experiment, pointing to a strong reduction of the ${\beta }_2^C$ charge deformation parameter in ${}^{24}$Ne. This follows the trend predicted for the evolution of the quadrupole deformation along the Ne isotopic chain.

Figure 1

Mass spectra of the most intense isotopic chains produced in the ${}^{22}$Ne+${}^{208}$Pb reaction. (a) Pure neutron transfer, (b) one-proton stripping, and (c) one-proton pickup reaction channels.

Figure 2

TKEL spectra for ${}^{22}$Ne ions detected by PRISMA (thin red line) and in coincidence with $\gamma$ transitions detected in CLARA (thick blue line). The shaded area is the difference spectrum corresponding to elastic events. Inset: Elastic cross section over Rutherford cross section as a function of the scattering angle. The experimental data (circles) have been normalized in the Rutherford region to the theoretical calculation performed by the code grazing (thin black line). The calculation performed by the ptolemy code (with the optical model parameters listed in Table ) is shown by the thick red line.

Figure 3

Inclusive angular distributions for the most intense reaction channels ${}^{22}$Ne, ${}^{23}$Ne, and ${}^{21}$F. Symbols correspond to experimental data, solid lines to theoretical calculations by the semiclassical model grazing[8].

Figure 4

$\gamma$ spectra of ${}^{22}$Ne, ${}^{23}$Ne, and ${}^{21}$F. In each spectrum the $\gamma$ transition from the first excited state to the ground state is clearly visible. For ${}^{22}$Ne, the arrow indicates the position of the $4^{+}\to 2^{+}$ decay, at 2083 keV, not observed in this experiment.

Figure 5

(a) Angular distribution of ${}^{22}$Ne ions measured in coincidence with the $2^{+}\to 0^{+}$$\gamma$ transition of 1275 keV. Filled (open) symbols refer to the analysis performed on the $\gamma$ spectrum of ${}^{22}$Ne taking (not taking) into account the feeding from high-lying states around 5 MeV. Inset of (a): inelastic TKEL spectrum of ${}^{22}$Ne and the contribution coming from the $2^{+}\to 0^{+}$ $\gamma$ decay (shaded area). (b) Angular distribution of ${}^{24}$Ne, measured in coincidence with the $2^{+}\to 0^{+}$ $\gamma$ transition of 1982 keV. Inset of panel (b): elastic over the Rutherford cross section of ${}^{24}$Ne, as a function of the scattering angle. Experimental data are indicated by symbols, while theoretical calculations performed by the code ptolemy (grazing) are given by thick red (thin black) lines. Data for ${}^{24}$Ne are taken from Ref. [10]. (See text for details.)

Figure 6

Angular distributions of ${}^{22}$Ne and ${}^{24}$Ne measured in coincidence with the corresponding $2^{+}\to 0^{+}$ transitions. Symbols refer to data, lines to DWBA calculations performed by the ptolemy code, assuming different values for the parameters ${\beta }_2^C$ and ${\beta }_2^N$, as given in the legends. (See text for details.)

Figure 7

(a) Quadrupole deformation parameter ${\beta }_2^C$ of the nuclear charge distribution, along the isotopic Ne chain, as derived from experiments. Filled diamonds refer to this work, open diamonds to a similar analysis performed by Gross et al. [18], open circles to the experimental adopted values [20], filled circles to the most recent results from Coulomb excitation experiments [21, 22, 23, 24]. (b) Theoretical predictions for the ground state deformation parameter ${\beta }_2^{\mathrm{gs}}$, as indicated by the legend [26, 27, 28]. (See text for details.)