Collective rotational motion in the N=Z nucleus Ar-36

A superdeformed rotational band has been identified in the N = Z nucleus Ar -36, firmly linked to known low-spin states, and observed to its high-spin termination at I-pi = 16(+). Lifetime measurements by the Doppler shift att enuation method establish a large low-spin deformation (beta (2) approximat e to 0.46) and a decrease in the collectivity as the band approaches termin ation. Comparisons with cranked Nilsson-Strutinsky and large-scale spherica l shell model calculations lead to a consistent description of the band bas ed on a configuration in which four particles are promoted to the pf shell. With two major shells active for both protons and neutrons, yet a valence space dimension small enough to be approached from the shell model perspect ive, this band offers an excellent opportunity to investigate the microscop ic structure of collective rotational motion in nuclei.