Systematics of reduced B(E3) transition probabilities for E3 transitions in even-A nuclei in 50 ≤ Z ≤ 92 region

In the nuclear landscape, many isomeric states near the shell closure decay via enhanced electric octupole $\left(E3\right)$ transitions. The enhancement in the transition strength is linked to the nuclear interactions between shell-model orbitals near the Fermi level that differ by $\Delta j=\Delta l=3$, involving high-$j$ intruder orbitals. The present study investigates the systematics of reduced $B\left(E3\right)$ transition probabilities in even-A nuclei with proton numbers $Z=50-92$. Experimental data were taken from the ENSDF, NSR and XUNDL databases. For recently measured $E3$ transitions, updated half-lives and branching ratios were used to determine refined $B\left(E3\right)$ values, calculated using the RULER code. The observed systematic trend across various closed shells indicates that the octupole correlations are strongly developed in the heavier mass region. The transition rates were further analysed according to the type of $E3$ transition and their underlying configurations. The results reveal a clear pattern: nuclei with configurations involving octupole-driving orbitals show significantly enhanced $B\left(E3\right)$ values, whereas the spin-flip and single-particle $E3$ transitions exhibit much weaker strengths.