| Popis: |
19F NMR spin echoes, following a 90°—τ—180° pulse sequence, have been observed from two samples of fluoridated powdered rat bone which have very low fluoride spin densities (≈ 11000 and 1300 relative to protons in water). Both echo envelopes show two distinct components, indicating at least two different local fluoride environments. By considering the well-known similarity between the mineral hydroxyapatite and bone mineral, we have associated the shorter of these components (Gaussian decay time ≈ μs) with fluoride sites having, for the most part, two fluoride nearest neighbors and the longer component (exponential decay time ≈ 300 μs in one sample and ≈400 μs in the other) with fluoride sites having only proton nearest neighbors. Using the second moment for F-F interactions, we estimated a lower bound for typical fluoride chain lengths in these samples. |
