The Lifetime of the Lowest 6+ State in 54Fe and E2 Effective Charge

The lifetime of the lowest 6 ⁺ state in ⁵⁴ Fe was measured by the β ⁺ -γ delayed coincidence method in the decay of the 1.43 min ⁵⁴ Co isomer. The half life was determined to be 1.24±0.04 nsec and B (E2: 6 ⁺ →4 ⁺ )=38.9±1.3 e ² f m ⁴ . Assuming pure πf _7/2 ^-2 configuration both for the 6 ⁺ and 4 ⁺ states in ⁵⁴ Fe, the polarization charge of the 0f _7/2 proton (δ e _eff ) with ⁵⁶ Ni as a core is deduced to be 0.9 e . From comparison with theoretical calculations a contribution to δ e _eff due to the 2\(\hslash\omega\) excitation of an inert core is found to be nearly the same in ⁴⁸ Ca and ⁵⁶ Ni.