Competition of different coupling schemes in atomic nuclei

Shell model calculations reveal that the ground and low-lying yrast states of the N = Z nuclei Pd-92(46) and Cd-96 are mainly built upon isoscalar spin - aligned neutron - proton pairs each carrying the maximum angular momentum J = 9 allowed by the shell 0g(9)/(2) which is dominant in this nuclear region. This mode of excitation is unique in nuclei and indicates that the spin - aligned pair has to be considered as an essential building block in nuclear structure calculations. In this contribution we will discuss this neutron - proton pair coupling scheme in detail. In particular, we will explore the competition between the normal monopole pair coupling and the spin - aligned coupling schemes. Such a coupling may be useful in elucidating the structure properties of N = Z and neighboring nuclei.