Calcium carbonates such as calcite are the dominant hosts of inorganic iodine in nature and are potentially important for the retention and removal of radioactive iodine isotopes (129 I and 131 I) in contaminated water. However, little is known about the structural environment of iodine in carbonates. In this study, iodate (IO 3 −) doped calcite and vaterite have been synthesized using the gel-diffusion method at three NaIO 3 concentrations (0.002; 0.004; 0.008 M) and a pH value of 9.0, under ambient temperature and pressure. Inductively coupled plasma mass spectrometry (ICP-MS) analyses show that iodine is preferentially incorporated into calcite over vaterite. Synchrotron iodine K-edge X-ray absorption near-edge structure (XANES) spectra confirm that IO 3 − is the dominant iodine species in synthetic calcite and vaterite. Analyses of iodine K-edge extended X-ray absorption fine structure (EXAFS) data, complemented by periodic first-principles calculations at the density functional theory (DFT) levels, demonstrate that the I 5+ ion of

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Quartz grains from the McArthur River uranium deposit of the Athabasca Basin, Saskatchewan, are characterized by three distinct types of cathodoluminescence (CL): 1) halos surrounding U-and Th-bearing mineral inclusions, and 2) patches and 3) continuous rims along grain boundaries and fractures. These three types of CL have a constant width of ~35 to 45 m, consistent with the maximum depth of penetration of alpha particles, and therefore they record alpha-particle-induced radiation damage. Relative to the host grains, the radiation-damaged areas are characterized by pronounced but broad CL bands in the ultraviolet (~350 nm) and red (~620-650 nm) regions. Isochronal annealing experiments reveal that the ultraviolet CL persists to 500°C but is annealed out at 600°C, whereas the red CL persists to at least 800°C. Electron paramagnetic resonance (EPR) spectroscopy, including detailed measurements on saturation behavior and thermal properties, revealed six paramagnetic defects: one oxygen vacancy center (E 1 '), three silicon vacancy hole centers and two O 2 -peroxy centers. Spectral simulations confi rm the presence of these centers. Moreover, EPR spectra of HF-treated samples show that the silicon vacancy-hole centers and the peroxy centers are concentrated in the radiation-damaged rims and fractures. Center E 1 ' appears to occur throughout the quartz grains and is annealed out at ~500°C; it thus cannot be responsible for the ultraviolet or red CL. The silicon vacancy-hole centers are all annealed out between 550° and 600°C, similar to the annealing temperature of the ultraviolet CL. The peroxy centers are the only paramagnetic defects stable above 600°C, corresponding to the preservation of red CL in radiation-damaged areas at high temperatures. Therefore, the silicon vacancy-hole centers and the peroxy centers are probably responsible for the characteristic ultraviolet and red CL, respectively, associated with radiation-damaged halos, patches and rims in quartz.

Borates are built from the [Bϕ3] planar triangles and the [Bϕ4] tetrahedral groups, where ϕ denotes O or OH. However, the [Bϕ4] groups in some borates are highly distorted to include three normal B-O bonds and one anomalously long B-O bond and, therefore, are best described as the [OBO3] pyramids. Four synthetic borates of the boracite-type structures (Mg3B7O13Br, Cu3B7O13Br, Zn3B7O13Cl, and Mg3B7O13Cl) containing a range of [OBO3] pyramids were investigated by multifield (7.05, 14.1, and 21.1 T) (11)B magic-angle spinning nuclear magnetic resonance (MAS NMR), triple quantum (3Q) MAS NMR experiments, as well as density functional theory calculations. The high-resolution (11)B MAS NMR spectra supported by theoretical predictions show that the [OBO3] pyramids are characterized by isotropic chemical shifts δiso((11)B) from 1.4(1) to 4.9(1) ppm and nuclear quadrupole parameters CQ((11)B) up to 1.3(1) MHz, both significantly different from those of the [BO4] and [BO3] groups in borates. These δiso((11)B) and CQ((11)B) values indicate that the [OBO3] pyramids represent an intermediate state between the [BO4] tetrahedra and [BO3] triangles and demonstrate that the (11)B NMR parameters of four-coordinate boron oxyanions are sensitive to local structural environments. The orientation of the calculated unique electronic field gradient tensor element Vzz of the [OBO3] pyramids is aligned approximately along the direction of the anomalously long B-O bond, corresponding to B-2pz with the lowest electron density.

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