Ratios of Relative Abundance, Magnetic Moments, and Capture Cross Sections of Gadolinium Isotopes from Paramagnetic Resonance Spectrum
Precision measurements on the hyperfine structure of the transitions corresponding to ∆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%; Gd155, 15.05+/-0.2% Gd157, 15.5+/-0.2%. Ratio of magnetic moments: μ155μ157=0.7495+/-0.0045. Irradiation of crystals at the Harwell pile with a thermal neutron flux of 1.2×1012 n/cm2 sec, and a fast flux of 2.3×1011 n/cm2 sec, yields the ratio of nuclear capture cross sections σ157σ155=2.82, using the above abundance values. No F-center spectrum was detected in crystals irradiated with a total neutron flux of about 1018 n/cm2. The paramagnetic resonance spectrum of gadolinium in irradiated crystals is unchanged, indicating negligible radiation damage in the neighborhood of the paramagnetic ions.