Deformation parameters and transition probabilities for shears bands in Pb isotopes

Abstract

Tilt angles, deformation parameters, angular momenta, and reduced magnetic dipole and electric quadrupole transition probabilities are calculated within the framework of the tilted-axis cranking model for shears bands in the neutron-deficient Pb isotopes 193 Pb to 202 Pb. The self-consistently calculated quadrupole-deformation parameters for the various configurations lie around ε 2 = −0.1, and the triaxiality is small. The tilt angle, i.e., the angle between the angular momentum and the nuclear symmetry axis, remains almost constant within each band, showing only a small increase toward higher angular momenta. The angular momentum increases mainly due to the shears effect, which is a step-by-step alignment of high-j proton and neutron orbitals into the direction of the total angular momentum. Calculated and experimental M1 transition rates are in good agreement. They decrease with increasing spin within the bands as expected for the shears effect. The calculated B(E2) values show only a weak spin dependence. However, the experimental B(E2) values have large errors, and more accurate data are needed to decide between the present model and a recently suggested geometrical approach.

Tilted axis cranking covariant density functional theory and its applications

“…In the left panel of Fig. 1, the calculated total angular momenta for one of the MR bands, Band 1, in 198 Pb as a function of the rotational frequency are shown in comparison with the data [30] and the PQTAC results [31]. It is found that both the tilted axis cranking CDFT and the PQTAC results agree well with the experimental data.…”

Magnetic rotations in198Pb and199Pb within covariant density functional theory

“…Similar investigations along this line have been extended for three-dimensional cranking and the nuclear chirality is proposed [17]. Because of the high numerical complexity of the TAC model, even today most of the applications are based on simple phenomenological Hamiltonians, such as the pairing plus-quadrupole-quadrupole tilted-axis cranking (PQTAC) model [18]. Only recently nonrelativistic [19] and relativistic [20][21][22] codes have been developed for microscopic investigations of magnetic rotation in the framework of density functional theory.…”

High-spin spectroscopy ofCe139

“…The less satisfactory agreem ent for the highest observed spins can be due to a gradual shape change as recently observed in the 141 Nd isotope [6]. The calculated B(M 1) values decrease with increasing rotation frequency from 5 ^ for hw -0.1 to 3 n l for Hco = 0.6, indicating the presence o f the shears-bands m echanism [36].…”