Is the 4.742 MeV state in 88Sr the 1− two-phonon state?

Abstract:: A nuclear resonance fluorescence experiment on ⁸⁸Sr has been performed with bremsstrahlung of 6.7 MeV endpoint energy. The γ-ray linear polarisation has been measured with a EUROBALL CLUSTER detector used as a Compton polarimeter. The results indicate positive parity for the J= 1 state at 4.742 MeV in ⁸⁸Sr, in contrast to the previous interpretation as a 1⁻ two-phonon (2⁺₁⊗ 3⁻₁) state and in conflict with the predictions of the quasiparticle-phonon model. On the basis of such calculations the 1⁺ state at 3.486 MeV may be considered as the 1⁺₁ one-phonon state and the very strong 1⁺₁→ 0⁺₁ deexcitation as proton spin-flip 2p_1/2→ 2p_3/2 transition.