Magnetic Hyperfine Fields Acting on Heavy Nuclei Recoiled into Iron, Cobalt, and Nickel

Abstract

Hyperfine fields acting on heavy nuclei recoiled into magnetic lattices following Coulomb excitation have been measured for ${}_{}{}^{184,186}{}_{}{}^{}\mathrm{W}$ and ${}_{}{}^{148}{}_{}{}^{}\mathrm{Nd}$ in iron, cobalt, and nickel lattices by means of angular-distribution or double-ratio measurements on the de-excitation gamma radiation. From such measurements both the magnitude and the sign of the hyperfine field can be determined. Moreover, information concerning the time scale on which the hyperfine field is established can be deduced by making the assumption that for pure rotational states $g_{2+}=g_{4+}$. From the internal consistency of the data for 2+ and 4+ levels in ${}_{}{}^{182}{}_{}{}^{}\mathrm{W}$ and ${}_{}{}^{184}{}_{}{}^{}\mathrm{W}$ and the 2+ level in ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$, it can be concluded that electronic and magnetic relaxation effects in magnetic lattices are short compared to the lifetime of the 4+ state in ${}_{}{}^{184}{}_{}{}^{}\mathrm{W}$ (6×${10}^{-11\mathrm{}}$ sec), although the data on the 4+ state in ${}_{}{}^{186}{}_{}{}^{}\mathrm{W}$ (4×${10}^{-11\mathrm{}}$ sec) suggest an upper limit to such relaxation times. The ratio of the hyperfine fields acting on tungsten recoiled into iron and cobalt is 1:0.7, in good agreement with published data for other transition elements in these matrices. The sign of the hyperfine field is negative in the case of tungsten, and positive in the case of neodymium, guest atoms.