A=9isospin quartet

Abstract

New measurements of the mass excess of the lowest $T=\frac{3}{2}$ levels in ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{B}$ give values of 25.7406±0.0017 and 27.0711±0.0023 MeV, respectively, and indicate a definite cubic dependence for the masses of the $A=9\mathrm{}$ quartet which includes ${}_{}{}^9{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^9{}_{}{}^{}\mathrm{C}$ in their ground states. A value of 7.6±1.7 keV is obtained for the coefficient of the $T_z^{}{}_{}{}^3$ term which now clearly exceeds the current theoretical estimates. Precise values of excitation energy of levels in ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ have been obtained as part of these measurements.