Ratios of Relative Abundance, Magnetic Moments, and Capture Cross Sections of Gadolinium Isotopes from Paramagnetic Resonance Spectrum

Abstract

Precision measurements on the hyperfine structure of the transitions corresponding to $\ensuremath{\Delta}M=4$ of the cubic-field paramagnetic resonance spectrum of gadolinium in single crystals of thorium oxide yield the following values: isotopic abundance: even isotopes, 69.45%; ${\mathrm{Gd}}^{155}$, 15.05\ifmmode\pm\else\textpm\fi{}0.2%; ${\mathrm{Gd}}^{157}$, 15.5\ifmmode\pm\else\textpm\fi{}0.2%. Ratio of magnetic moments: $\frac{{\ensuremath{\mu}}^{155}}{{\ensuremath{\mu}}^{157}}=0.7495\ifmmode\pm\else\textpm\fi{}0.0045$.Irradiation of crystals at the Harwell pile with a thermal neutron flux of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{12}$ n/${\mathrm{cm}}^{2}$ sec, and a fast flux of 2.3\ifmmode\times\else\texttimes\fi{}${10}^{11}$ n/${\mathrm{cm}}^{2}$ sec, yields the ratio of nuclear capture cross sections $\frac{{\ensuremath{\sigma}}^{157}}{{\ensuremath{\sigma}}^{155}}=2.82$, using the above abundance values.No $F$-center spectrum was detected in crystals irradiated with a total neutron flux of about ${10}^{18}$ n/${\mathrm{cm}}^{2}$. The paramagnetic resonance spectrum of gadolinium in irradiated crystals is unchanged, indicating negligible radiation damage in the neighborhood of the paramagnetic ions.