Search for octupole deformation in $A \sim 225$ Po-Fr nuclei.

Evidence of static octupole deformation can be found only in selected regions of the nuclear chart ({A\sim $146$ and $A\sim 222$), where orbitals differing by $\Delta$ j, $\Delta$ l = $3$ approach the Fermi level for both protons and neutrons. $A\sim 225$ Rn-Th nuclei are expected to show the largest static octupole deformations, as highlighted by recent experimental measurements and by theoretical calculations. Very few direct measurements of $E3$ transitions were performed in recent years in $^{220}Rn$, $^{224}Ra$ and $^{228}Th$ highlighting a typical de-excitation pattern. We performed an experiment at GSI in April 2021 within the DESPEC Collaboration experimental campaign, with the aim to search for evidence of octupole deformation in $220