Hyperfine Interactions and the Magnetic Fields Due to Core Polarization inFe57

Magnetic-dipole hyperfine-interaction constants have been measured for the ${}_{}{}^5{}_{}{}^{}D_{4,3,2,1}^{}{}_{}{}^{}$ states of the ground term of ${\mathrm{Fe}}^{57}$ in an atomic-beam magnetic-resonance experiment. The values are $a_J=38.0795\mathrm{}\mathrm{}\left(10\right), 26.351\mathrm{}\left(2\right),18.762\mathrm{}\mathrm{}\left(2\right), \mathrm{and} 14.077\mathrm{}\left(5\right)\mathrm{}$ Mc/sec for $J=4, 3, 2, \mathrm{and} 1$, respectively. The deviations of the ratios of these $a$ factors from theoretical predictions are ascribed to core polarization, and the implications of this assumption are discussed.