The $g$-factor of the 12$^+$ isomeric state in $^{206}$Pb and the effective orbital $g$-factor of the neutron

The g -factor of the 12 + two-quasiparticle isomeric state, ¦(v i 13 2 ) −2 ¦ 12+ , in 206 Pb has been measured by the time-differential perturbed angular correlation method. The result obtained is g (12 + , 206 Pb) = − 0.155 ± 0.004. Three different methods are applied to deduce the orbital g -factor of the neutron around the 208 Pb core, namely (i) the M1 core polarization model, (ii) the configuration mixing model, and (iii) a combination of the M4 transition rate in 207 Pb with the present result. The g l eff (neutron) deduced in the three different ways are in good internal agreement: (i) − 0.036 ± 0.010, (ii) − 0.040 ± 0.03 and (iii) −0.034 ± 0.010. Although it is hard to estimate the overall uncertainty, it is probably significant that the anomaly in the orbital g -factor of the neutron has opposite sign from that of the proton, and that the size is smaller.