Sorption of actinides, particularly plutonium, onto submicrometer-sized colloids increases their mobility, but these plutonium colloids are difficult to detect in the far-field. We identified actinides on colloids in the groundwater from the Mayak Production Association, Urals, Russia; at the source, the plutonium activity is approximately 1000 becquerels per liter. Plutonium activities are still 0.16 becquerels per liter at a distance of 3 kilometers, where 70 to 90 mole percent of the plutonium is sorbed onto colloids, confirming that colloids are responsible for the long-distance transport of plutonium. Nano-secondary ion mass spectrometry elemental maps reveal that amorphous iron oxide colloids adsorb Pu(IV) hydroxides or carbonates along with uranium carbonates.

Single crystals LiGaX 2 (X = S, Se, Te) of optical quality were grown, with transparency ranges at 5 cm -1 absorption level of 0.32-11.6 µm, 0.37-13.2 µm and 0.54-14.2 µm, respectively. The first two, LiGaS 2 and LiGaSe 2 , have a wurtzite-type structure whereas LiGaTe 2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the whole transparency ranges of LiGaS 2 and LiGaSe 2 and n a and n c were found to be very close (quasi-uniaxial optical anisotropy) with a crosspoint at 6.5 µm (LiGaS 2 ) and 8 µm (LiGaSe 2 ). Sellmeier equations were fitted and phase-matching conditions for second harmonic generation (SHG) were calculated: the 1.467-11.72 µm spectral range for the fundamental is covered by LiGaS 2 and LiGaSe 2 .

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The chalcopyrite crystal LiGaTe 2 was grown by the Bridgman-Stockbarger technique with sufficient size and optical quality that allowed the characterization of its linear (dispersion and birefringence) and nonlinear optical properties. X-ray structural analysis was performed on single crystals. The transmission was recorded in the 0.5-24 µm range, and Raman and IR-spectra were recorded in the 0-400 cm -1 and 180-400 cm -1 ranges, respectively. The clear transparency range of LiGaTe 2 extends from 2.5 to 12 µm, the band-gap at room temperature is at 2.41 eV (515 nm), residual absorption limits the transmission near the band-edge, and the upper limit for the transmission is determined by the onset two-phonon absorption. LiGaTe 2 is a positive uniaxial crystal that possesses sufficient birefringence for phasematching. Its nonlinear coefficient d 36 was estimated by phase-matched second harmonic generation to be 43 pm/V ( 10%. It is only the third crystal belonging to the A I B III C 2 VI chalcopyrite family for which phase-matched nonlinear frequency conversion could be demonstrated, and of this group it exhibits the highest nonlinearity and figure of merit for nonlinear optical applications in the mid-infrared.