Clustering effects in ${}^{48}\mathrm{Cr}$ composite nuclei produced via the ${}^{24}\mathrm{Mg}+{}^{24}\mathrm{Mg}$ reaction

The nuclear properties of ${}^{48}\mathrm{Cr}$ composite $\alpha$-like nuclei produced at 60 MeV of excitation energy via the ${}^{24}\mathrm{Mg}+{}^{24}\mathrm{Mg}$ reaction were investigated. This excitation energy corresponds to a resonance with a narrow width (170 keV) observed in the elastic and inelastic channels, which was interpreted as a highly deformed state. To gain insight on the deformation of this state exclusive measurements of light charged particles were carried out with $8\pi \mathrm{LP}$ apparatus at Laboratori Nazionali di Legnaro and compared to statistical model predictions. The measured of $\alpha$-particle energy spectra, $\alpha$-evaporation residues, $\alpha \text{−}\alpha$, and $\alpha \text{−}\alpha \text{−}\alpha$ correlations indicate the limitation of the rotating liquid drop model in describing the nuclear shape of the compound nucleus along the decay cascade. To reproduce the full set of experimental data very elongated nuclear shapes had to be considered, with an axis ratio $3:1$ at the resonance angular momentum. This large deformation is consistent with previous findings for $\alpha$-like nuclei and with the predictions of the cranked cluster model.

Figure 1

(a) Schematic layout of the experimental apparatus. The letters from A to G label the seven rings of the ball section. (b) Layout of the PPAC system.

Figure 2

Time of flight spectra of fragments detected in one PPAC sector normalized to the maximum. The black line is the ToF spectrum produced without any of the trigger conditions, with the OR of all signals bombarding the ${}^{24}\mathrm{Mg}$ target; the green line is the ToF spectrum produced using the ${}^{12}\mathrm{C}$ target and the Ball coincidence condition; the red line is the spectrum produced using the ${}^{24}\mathrm{Mg}$ target and the Ball coincidence condition. See text for details.

Figure 3

Experimental and calculated angular differential multiplicity distributions for $\alpha \text{−}\mathrm{particles}$ versus the Ball detector identification number. Black dots represent the experimental data. The blue and red lines are the ND and HD simulations, respectively. See the text for details.

Figure 4

Experimental and calculated $\alpha$-particle energy spectra in the laboratory system. Black and red dots represent the experimental data. The blue and red lines are the ND and HD simulations, respectively. The two experimental spectra were measured with two different PPACs and two different Ring D telescopes. All the spectra are normalized to the maximum. See the text for details.

Figure 5

(a) Experimental and calculated $\alpha \text{−}\alpha$ angular correlations particles versus the ball detector identification number. Black dots represent the experimental data. The blue and red lines are the ND and HD simulations, respectively. (b) Schematic view of an $\alpha \text{−}\alpha$ correlation event, where the reference ring (G) is shown in green and in gray for all the others. The two projections shown the correlation angles $\left(\mathrm{\Delta }\beta ,\mathrm{\Delta }\gamma \right)$ of the second $\alpha$ particle, $\alpha$-Det, with respect to the first one $\alpha$-Trigger. See the text for details.

Figure 6

(a) Experimental and calculated angular distributions of $\alpha$-particle coincidences. According the schematic (b), two $\alpha$ particles (${\alpha }_{1\mathrm{T}}$ and ${\alpha }_{2\mathrm{T}}$) measured in the same plane identify the CN spin direction, the third one defines the $\eta$ angle with respect to the spin direction. Black dots represent the experimental data. The blue and red lines are the ND and HD simulations, respectively. The distributions are normalized at $\eta ={10}^{\circ }$. See the text for details.