▪ Abstract  This chapter reviews the experimental properties of shears bands. The most puzzling characteristic of these structures is the emergence of rotational-like behavior while the nucleus retains a small quadrupole deformation. Regardless of the details of particular theoretical models, it can be shown that the most important degree of freedom in describing the shears mechanism is the shears angle. It is then possible to develop a semiclassical description of the shears mechanism, in which the nature (multipole order) of the interaction between valence protons and neutrons constituting the shears “blades” may be derived and the dynamics of the system described. We discuss the competition between the shears mechanism and collective rotation and mention the connection to “magnetic rotation.” Directions for future theoretical and experimental efforts are suggested.

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By deriving the angle between the proton and neutron spin vectors j ជ and j ជ in the shears bands in 198,199 Pb, we present a semiclassical analysis of the B(M 1) and B(E2) transition probabilities as a function of the shears angle. This provides a semiempirical confirmation of the shears mechanism proposed by Frauendorf using the tilted-axis-cranking model. In addition, we propose that the rotational-like behavior observed for these bands may arise from a residual proton-neutron interaction. ͓S0556-2813͑98͒51303-9͔

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