Stability and instability of nuclei in the mass region A=68-82 based an exotic cluster decay studies

The stability or instability of nuclei in the mass region A = 68-82 with 34 less than or equal to Z less than or equal to 40 is studied on the basis o f the cluster decay process in these nuclei. The nucleus Kr-76 is found to be the most stable nucleus in this region, and that, in each case, moving a way from the most stable isotope by the addition or subtraction of neutrons , the resulting parent nuclei are found to be highly unstable against all p ossible (Q > 0) cluster decays. Such an extra stability at Z = 36 and Ar = 40 points to the possible existence of new shell stablilizing effects at th ese nucleon numbers, which can be understood as reinforcing of the (deforme d) Z = 36 stable shell with the (spherical/deformed) N = 40 stable shell, r esulting in a superdeformed Kr-76 nucleus. The instability with both the ad dition and subtraction of neutrons is due to major shell closure of the dau ghter products. In view of the possible consequences of this paper for both nuclear structure and cold fusion studies, further calculations are called for the shell gaps and the possible use of these nuclei as cold reaction p artners.