The β-NQR (nuclear quadrupole resonance) signals of ${}^8\mathrm{B}$ ($I^{\pi }=2^{+},T_{1/2}=770$ ms) implanted in ${\mathrm{TiO}}_2$ (rutile) have been detected to determine the electric quadrupole moment of ${}^8\mathrm{B}$ with high precision. The ratio of the quadrupole moments of ${}^8\mathrm{B}$ and ${}^{12}\mathrm{B}$ was determined as $|Q$(${}^8\mathrm{B}$)$/Q$(${}^{12}\mathrm{B}$)$|=4.88\pm 0.04$. Combined with the known sign, the quadrupole moment of ${}^8\mathrm{B}$ was obtained as $Q$(${}^8\mathrm{B}$)$=+(64.5\pm 1.4)$ mb, which is consistent with and more precise than the previously reported value. The experimental values of the $Q$ moment, the proton and neutron radii and the density distribution of ${}^8\mathrm{B}$ were compared with several theoretical predictions and were found to be best reproduced by a microscopic cluster model, which suggests the existence of a proton halo.

• Received 6 April 2006

DOI:https://doi.org/10.1103/PhysRevC.74.024327