$\alpha :2n:\alpha$ Molecular Band in ${}^{10}\mathrm{Be}$

The 10.15 MeV resonance in ${}^{10}\mathrm{Be}$ has been probed via resonant ${}^6\mathrm{He}+{}^4\mathrm{He}$ elastic scattering. It is demonstrated that it is the $J^{\pi }=4^{+}$ member of a rotational band built on the 6.18 MeV $0^{+}$ state. A ${\Gamma }_{\alpha }$ of 0.10–0.13 MeV and ${\Gamma }_{\alpha }/\Gamma =0.35–0.46$ were deduced. The corresponding reduced $\alpha$ width, ${\gamma }_{\alpha }^2$, indicates one of the largest $\alpha$-cluster spectroscopic factors known. The deformation of the band, including the 7.54 MeV, $2^{+}$ member, is large (${\hslash }^2/2I=200\mathrm{keV}$). Such a deformation and the significant degree of clusterization signals a well-developed $\alpha :2n:\alpha$ molecular structure.

Figure 1

Experimental setup. The region in the gas volume in which the 10.15 MeV ${}^{10}\mathrm{Be}$ resonance is formed is indicated (shaded zone). The resonance subsequently decays into ${}^6\mathrm{He}+{}^4\mathrm{He}$ which are detected in coincidence in the LAMP array.

Figure 2

The reconstructed center-of-mass emission angle (${\theta }_{\mathrm{c}.\mathrm{m}.}$) vs the interaction distance. The left-hand panel shows the experimentally determined distribution, and the right the result of simulations for a resonance at 10.15 MeV with $\Gamma =296\mathrm{keV}$ [6] and $J^{\pi }=4^{+}$.

Figure 3

Experimentally determined center-of-mass distribution (data points) compared with simulations for the decay of a spin 4 (blue-solid line), 2 (red-dashed line), and 6 (black-long-dashed line) resonance. The inset shows the energy-spin systematics of the rotational band of which the present $4^{+}$ state is a member.

Figure 4

Normalized angular distributions for the singles data measured at beam energies of 11.1 ($\mathrm{\text{circles}}\times 10$), 7.5 ($\mathrm{\text{squares}}\times 1$), and 6.1 MeV ($\mathrm{\text{triangles}}\times 0.1$). The solid lines overlaid over the three data sets correspond to the elastic scattering as simulated by the Monte Carlo calculations. The dotted line shows the Rutherford scattering contribution for the 7.5 MeV data.