“Shears bands” in 199Pb and 200Pb

High-spin level scheme ofPb194

“…Angular momentum and excitation energy along the bands are increased by a step-by-step alignment of proton and neutron spins in the direction of the total angular momentum. Since this resembles the closing of a pair of shears, the M1 bands have also been called "shears bands" [8]. With the increasing spin the values of the reduced transition probabilities B(M1) gradually decrease, as confirmed by lifetime measurements (see, e.g., Ref.…”

“…Such sequences were found for the first time in 199,200 Pb by Baldsiefen et al [8] and were called "shears bands" or magnetic rotational (MR) bands. They are built on weakly deformed oblate states and manifest a completely new way of generating the nuclear spin.…”

“…The intruder proton configuration of (s −2 1/2 h 2 9/2 ) is proposed to be the main configuration for the 0 + 2 state [27][28][29] (at 931 keV; not seen in the present experiment) and for the 8 + 1 state (e.g., Ref. [8] and references therein), and g-factor measurements [5] revealed a π (s −2 1/2 h 1 9/2 i 1 13/2 ) configuration for the 11 − 1 isomer. As previously mentioned, excitations across the Z = 82 gap to these intruder proton orbitals are known to drive the nucleus to stable collective oblate shapes.…”

“…The structures built directly on such oblate states, however, do not correspond to the expected rotational bands but resemble the spherical multiplet-like pattern. In competition with these excitations, regular cascades of strongly enhanced M1 transitions were observed in Pb isotopes some years ago [8] and have been studied extensively. As a result, a new mechanism of nuclear excitations-named magnetic rotation-has been established.…”

“…After the discovery of magnetic bands in 199,200 Pb [8], the neighboring Pb isotopes attracted many studies [16,17]. Nevertheless, the level schemes of most of the nuclei are incomplete with bands not connected to the lower lying levels.…”