The influence of internuclear dipole-dipole and electron-nuclear dipolar interactions on the NMR spectrum shape was examined for UF,. It is shown that only the dipolar interaction of the l9F nuclei with the magnetic moments of the U4+ ions leads t o such a broad NMR spectrum in polyrrystalline UF, that there is no ground for separating it into several components corresponding to the seven nonequivalent fluorine nuclei in the UF, structure. A certain additional broadening of the experimental spectrum may be accounted for by anisotropic hyperfine interaction, due t o the transfer of the spin density from UZt to fluorine. On studying the magnetic susceptibility of UF, in the region of helium temperatures, Leask et al.[l] arrived a t the conclusion that the theoretical magnetic moment of the U4+ ion is essentially larger than the observed one either on account of indirect interaction or due t o the "spread" of unpaired electrons of the U4+ ions along the adjacent surroundings. The transfer of spin density t o fluorine atoms in UF, should lead to hyperfine interaction of fluorine nuclei with unpaired electrons which, in principle, may be detected by the NMR and ESR methods.Schulman and Jaccarino [a] noted that in the case of the 19F NMR spectrum of uranium tetrafluoride there is no isotropic shift which could be ascribed t o isotropic hyperfine interaction. However, later it was noted [3] that the absence of a spectrum shift simply indicates that the isotropic component of the hyperfine interaction is equal to zero, whereas the anisotropic component, leading t o a broadening of the spectrum and to no subsequent shift, may have a nonzero value. I n other words, this signifies that 2p states, and not 2s states, of fluorine are liable for mixing with the magnetic states of the U4+ ion. Hov ever, in order to discover the above-said anisotropic hyperfine interaction by means of the polycrystal NMR spectrum (UF4 monocrystals of sufficient size cannot yet be obtained), i t is essential to account for several factors which likewise lead t o a broadening of the spectrum.Pintar in his recent paper [4], however, gave a different interpretation for the l9F NMR spectra in UF,. Thus, he explains thc absence of spectrum shift by the presence of seven non-equivalent fluorine nuclei in the structure of uranium 28 *

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