Precise experimental g factors of the first 2 ϩ states of 50 Ti, 52 Cr, and 54 Fe have been measured. They differ markedly from the g factors of the (7/2) Ϫ ground states of the odd-mass neighbors. The experimental results show that the g factors, g(2 1 ϩ ) and g"(7/2) Ϫ …, lie approximately on straight lines as a function of Z albeit with different slopes. Shell model calculations were performed in which up to t nucleons were excited from the f 7/2 shell. The data are reproduced by calculations using the FPD6 interaction with tϭ1. However, the slope flattens out in the calculations with higher t. The sign of a key matrix element which allows for f 5/2 admixture is positive for the FPD6, zero for the KB3, and negative for the FPY interactions, respectively, indicating that a better understanding of the effective interaction in this region is needed.PACS number͑s͒: 21.10. Ky, 25.70.De, 27.50.ϩe Core polarization is an effect which involves the excitation of an otherwise closed shell or inert core by valence nucleons. In general, such interactions result in a quenching of the magnetic moment of nuclear states, a pattern which has been observed in many g factor measurements ͓1,2͔. This phenomenon was predicted by Arima and Horie ͓3-5͔ in their early work on core polarization, in particular with respect to the Nϭ28 isotones of f p shell nuclei. These span a region ͑above doubly closed shell 40 Ca) from scandium ( 21 49 Sc) to cobalt ( 27 55 Co) where the ground state of the oddproton members have spin and parity (7/2) Ϫ corresponding to a f 7/2 n proton configuration. In the pure shell model, all configurations ͓(7/2) Ϫ ͔ n of the Nϭ28 isotones should have the same g factor. If the bare values for the proton g l ϭ1 and g s ϭ5.586 are used, this g factor is g( f 7/2 )ϭ1.655, the Schmidt value. This result holds specifically for the I ϭ(7/2) Ϫ ground states of the odd A nuclei and for the I ϭ2 1 ϩ states of the even-even nuclei. Any deviations from this result would provide evidence for core polarization in terms of configuration mixing and/or the presence of meson exchange currents.The very precise experimental g factors of the (7/2) Ϫ ground states of 51 V, 53 Mn, and 55 Co ͓6͔ in fact exhibit g factors significantly lower than the Schmidt value which, furthermore, differ from each other. As emphasized by Arima and Horie, core polarization accounts for both these features ͓3,4͔. Their first order perturbation theory calculations yield a substantial quenching of these g factors whose magnitudes increase linearly with the number of proton holes in the f 7/2 shell. As a consequence, the g factor of 55 Co ͑with one proton hole͒ is predicted to be smaller than that of 51 V ͑with five proton holes͒, as has been experimentally confirmed.Experimental data exist for the g factors of the first 2 ϩ states of the Nϭ28 isotones 54 Fe ͓7͔ and 52 Cr ͓8͔. In both cases, the g factors are substantially lower than those of their odd-mass neighbors. In order to understand this behavior the g factor of the remaining isotone, 50 Ti(2 ...
