Phase transition in exotic nuclei along the N = Z line

The abrupt structure change from the nuclei of N = Z <= 35 to those of N = Z >= 36 is investigated by means of shell model calculations. Basic features of all even-even and odd-odd nuclei under consideration are well reproduced. A sudden jump of nucleons into the upper g(9/2)d(5/2) shell at N = Z = 36 is found to be the main reason for the cause of the qualitative structure difference. It is argued that the structure change can be viewed as a decisive change of the mean field, or a phase transition, along the N = Z line. (c) 2007 Elsevier B.V. All rights reserved.