Impact of the continuum on the γ decay of the lowest 2+ states in 14C

The half-life, T 1/2 =14.6(33) fs, of the 7012-keV 2 1 + state in 14 C was measured in an experiment employing the 9 Be( 6 Li,p γ ) fusion-evaporation reaction and the GODDESS setup. The γ decay from the 2 2 + near-threshold resonance, located 142 keV above the 8176-keV neutron-emission threshold, was also investigated. An upper limit of 4.0 × 10 − 5 was established for the γ -decay branching ratio with respect to the neutron-decay channel. The B(E2) transition probabilities for these 2 1 + and 2 2 + states were compared to predictions from the Shell Model Embedded in the Continuum (SMEC). Significant modifications of these B(E2) probabilities, with respect to the standard shell model, are expected due to the coupling to the continuum. For calculations using the YSOX interaction, agreement was found for large negative values of V 0 , the coupling constant to the continuum. The central value V 0 = −645 MeV fm 3 results in a retardation by a factor ∼ 3.5 for the 2 1 + → 0 1 + transition, and an enhanced probability by a factor ∼ 2.5 for the γ -decay out of the 2 2 + state. The latter factor reflects the effect of collectivization of the 2 2 + excitation when the coupling to the continuum is taken into account.