The effects of the 2p-2h ground state correlation, isobar-hole excitation, pion pair current, and pionic current on the electromagnetic $M1\mathrm{}$ strength are calculated as a first order perturbation correction, for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Z}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ using Hartree-Fock wave functions. The isobar-hole contribution is the dominant quenching mechanism in heavier nuclei, though the enhancement effect of the pion pair current is not at all negligible. We also comment on the Gamow-Teller strength.

NUCLEAR STRUCTURE Calculated $M1\mathrm{}$ strength ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ including ground state correlation, isobar-hole excitation, meson exchange currents.

• Received 1 February 1982

DOI:https://doi.org/10.1103/PhysRevC.26.297