Hyperfine Structure and Nuclear Moments of 17-Hr Bromine-76

The nuclear spin, the nuclear magnetic-dipole interaction constant $a$, and the nuclear electric-quadrupole interaction constant $b$, have been determined for 17-hr bromine-76 by an atomic-beam experiment. The results are: $I=1\mathrm{}$, $\mathrm{}\left|a\right|=345.422\mathrm{}\pm 0.014$ Mc/sec, $\mathrm{}\left|b\right|=314.329\mathrm{}\pm 0.022$ Mc/sec, $\frac{b}{a}=0.9100\mathrm{}\pm 0.0001$. The nuclear magnetic-dipole and electric-quadrupole moments are calculated to be, respectively, $\mu =\pm 0.5479\pm 0.0001$ nuclear magneton, and $Q=\mp 0.27\pm 0.01$ barn. The sign of $\mu$, though not determined, is probably negative. The hyperfine structure separations are $\Delta \nu (\frac{5}{2}, \frac{3}{2})=1256.47\mathrm{}\pm 0.05$ Mc/sec, and $\Delta \nu (\frac{1}{2}, \frac{3}{2})=189.11\mathrm{}\pm 0.05$ Mc/sec. The hyperfine structure is of particular interest because the $F=\frac{1}{2} \mathrm{and} \frac{3}{2}$ levels are inverted and not in normal order. This inversion is the first case of its kind established in an atomic-beam experiment.