The polarization of radioactive gold nuclei in iron

The y-radiations from the nuclei of 198 Au, 199 Au and 195 Au polarized as diamagnetic impurities in ferromagnetic iron have been studied down to 0.012 °K, reached by thermal contact with an adiabatically demagnetized chrome potassium alum ‘heat sink’. Specimen temperatures were deduced from measurement of the anisotropic γ-ray emission from 60 Co nuclei polarized in the same iron alloy, and the importance of this new technique in extending the temperature range and consequently the accuracy of interpretation of the measurements is discussed. From observation of the 412 keV γ-ray in 198 Au and of the 158 keV γ-ray in 199 Au, two independent and self-consistent values of |H eff |, the hyperfine coupling field present at gold nuclei in iron, are obtained. The mean value is |H eff | = 1.35 ± 0.05 x 10 9 Oe. With this value the 195 Au measurements yield a nuclear magnetic dipole moment of ± (0*13 ± 0*04) n.m. for this isotope. The agreement of the value of |He ff | found in this work with that from Mössbauer studies of 197 Au in iron justifies the assumed application of the £ approximation to the first forbidden β-transitions in the decays. Values for the ratio A of the linear combinations of matrix elements, V∘ and Y 1 corresponding to j β = 0 and 1 respectively in the 959 keV β-decay of 198 Au and the 250 keV /?-decay of 199 Au are found to be ±(0.82 ± 0.18) and ± ( 1.86 +0.82 -0.34 ) respectively. These results are compared with calculations based on the nuclear single particle model.