Investigation of the high-spin yrast band structure of 236-246Pu isotopes

The available data on some actinide nuclei point to certain significant features of the rotational yrast band and other excited bands. The rotational properties of plutonium isotopes (236-346Pu) were studied via projected shell model (PSM). Calculations are based on the Hamiltonian of the PSM which includes the formed part of a single particle, the Q - Q force, and the residual interaction of monopole and quadrupole pairings. The results of the calculated energy levels of the yrast band are then compared with available experimental data and a good agreement has been found. The crossing between two-quasiparticle (2qp) excited bands and the ground state band (g band) in the high-spin regions has been analyzed in terms of band diagrams. The upbendings observed in the kinematic moments of inertia (j(1) MOI) curves for 236-346Pu isotopes are due to the effect of two aligning nucleons that occupy excited bands and the nu( j15/2), pi(i13/2) high -j intruder orbits. The PSM successfully reproduces the observed upbending in j(1) as well as the upturning and downturning in j(2). For the 240Pu isotope, the PSM predicts a simultaneous alignment of neutrons nu 2 [1/2, -7/2] K pi = 4+ and protons pi 2 [-3/2, 5/2] K pi = 1+ bands cross the g band at spin I = 22. We expect it to be mainly responsible for the disagreement at I = 22. Furthermore, electric quadrupole transition probabilities B(E2) and the gyromagnetic factor (g factor) for the yrast band energy levels are also studied.