A ridge structure consisting of stretched E2 transitions and extending from ħω≃0.6 to 0.75 MeV has been found in a proton-selected γ-γ matrix in the reaction ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^{37}$Cl, xn${)}^{152,153}$Dy at 187 MeV. The ridge spacing corresponds to a dynamic moment of inertia, ${\mathit{scrI}}^{\mathrm{}\left(2\right)\mathrm{}}$, of about 130${\mathrm{ħ}}^2$ ${\mathrm{MeV}}^{\mathrm{-}1}$ and suggests the existence of a hyperdeformed prolate shape with a quadrupole deformation ${\mathrm{\beta }}_2$≥0.9. Furthermore, a cascade of 10 discrete transitions with an average energy spacing of 30±3 keV has been found. This result is consistent with calculations indicating conditions favorable to hyperdeformed structures.

• Received 1 February 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.231