Competition Between Single-Particle and Collective Excitations in the Region of 30 $\leq$ Z $\leq$ 38 and 32 $\leq$ N $\leq$ 50*

The experimental data for the excitation energies and B(E2) reduced transition probabilities for the 2$^+_1$, 4$^+_1$ and 2$^+_2$ states in the long chains of stable and radioactive even-even isotopes of Zn, Ge, Se, Kr and Sr were examined in terms of the competition between single-particle and collective modes of excitation. The magic numbers of 28 and 50 were used for both protons and neutrons. While the level-energy information is not particularly infomative when plotted as a function of the neutron number $N$, the B(E2) values showed obvious trends towards collectivity as $Z$ increases towards the middle of the shell. The data were also analyzed as a function of the number of protons (proton holes) $N_p$ and neutrons (neutron holes) $N_n$ in the valence shells and of the parameter $P$ = $\frac{N_p N_n}{N_p + N_n}$. Increasing values of $P$ correspond overall to larger B(E2)'s but the scatter of the data indicates structures with complex wave functions.