Core breaking and possible magnetic rotation in the semimagic nucleus ^(90)Zr

The semimagic nucleus^(90)Zr,with Z=40 and N=50,is investigated in terms of large scale shell model calculations.A logical agreement is obtained between the available experimental data and predicted values.The calculated results indicate that the low-lying states are primarily dominated by the proton excitations from the fp orbitals across the Z=38 or 40 sub shell into the high-j 1g_(9/2)orbital.For the higher-spin states of^(90)Zr,the breaking of the N=50 core plays a crucial role,and the contribution of different orbitals to each state are discussed in this article.The evolution from neutron core excitations to proton excitations is systematically studied along the neighboring N=50 isotones.Furthermore,the strongΔI=1 sequence demonstrates an abrupt backbend attributed to the alignment of the valence nucleons in fp proton orbitals and is proposed to have aπ(fp)^(-2)(1g_(9/2))^(2)■v(1g_(9/2))^(-1)(2d_(5/2)/1g_(7/2))^(1)configuration before the backbend,based on the shell model calculations.The properties of this sequence before the backbend indicate a general agreement with the fingerprints of magnetic rotation;hence,the sequence with theπ(fp)^(-2)(1g_(9/2))^(2)■v(1g_(9/2))^(-1)(2d_(5/2)/1g_(7/2))^(1) configuration is suggested as a magnetic rotational band arising from shears mechanism.