Hyperfine structure of the $2\,^3\!P$ state in $^9$Be and the nuclear quadrupole moment

Abstract: We have performed accurate calculations of the hyperfine structure of the $2\,^3!P$ state in the $^9$Be atom with the help of highly optimized, explicitly correlated functions, accounting for the leading finite nuclear mass, radiative, nuclear structure and relativistic effects. By comparison with measurements, we have determined the $^9$Be nuclear quadrupole moment to be $Q_{\rm N} = 0.05350(14)$ barns, which is not only the most accurate result, but also disagrees with previous determinations.