Spin, quadrupole moment, and deformation of the magnetic-rotational band head inPb193

Abstract

The spectroscopic quadrupole moment of the T 1/2 = 9.4(5) ns isomer in 193 Pb at an excitation energy E ex = (2585 + x) keV is measured by the time-differential perturbed angular distribution method as |Q s | = 2.6(3) e b. Spin and parity I π = 27/2 − are assigned to it based on angular distribution measurements. This state is the band head of a magnetic-rotational band, described by the coupling of a neutron hole in the 1i 13/2 subshell with the (3s −2 1/2 1h 9/2 1i 13/2 ) 11 − proton excitation. The pairing-plus-quadrupole tilted-axis cranking calculations reproduce the measured quadrupole moment with a moderate oblate deformation 2 = −0.11, similar to that of the 11 − proton intruder states, which occur in the even-even Pb nuclei in the region. This is the first direct measurement of a quadrupole moment and thus of the deformation of a magnetic-rotational band head.