Polarization ofCo57in Fe Metal

A study has been made of the effect of low temperature on the resonant emission and absorption of 14.4-kev Mössbauer radiation from ${\mathrm{Fe}}^{57}$ in Fe metal. Analysis of intensity changes in the hyperfine spectrum is made in terms of the Zeeman level splittings of the ground states of ${\mathrm{Fe}}^{57}$ absorbing nuclei and of the ground states of ${\mathrm{Co}}^{57}$ parent nuclei. The theory for the temperature dependence is developed in terms of the properties of the ${\mathrm{Co}}^{57}$ decay and of the subsequent gamma transitions. Experiments were carried out with a source of ${\mathrm{Co}}^{57}$ nuclei in Fe metal at temperatures between 4.5° and 0.85°K. The experimental results, analyzed in terms of the theory, yield a value of the hyperfine magnetic field at the ${\mathrm{Co}}^{57}$ nuclei. Comparison of the result with other pertinent experimental values indicates that depolarization of the nuclei by the $K$-capture decay of ${\mathrm{Co}}^{57}$ is not evident in the present material.