The spin-lattice relaxation of the S-state ion Gd3+ in a calcium tungstate host lattice has been examined at 37.5 GHz over the temperature range 1.5 to 30 K. The gadolinium concentrations in the doped single crystals used were about 50 ppm. Single exponential recovery was observed and the spin-lattice relaxation time (T 1) varied from about 14 msec at 1.5 K to 0.03 msec at 30 K, measured with θ=90° and φ=8°. It was found that T 1 varied with temperature (T) as T 1 ∝ T −1 below 8 K and as T 1 ∝ T −3 between 8 and 30 K. The experimental data was fitted by the expressions T 1 −1 =35 T+0.5 T 3 and T 1 −1 =35T+0.1 T 3.6 for crystals of nominal gadolinium concentrations 0.005 wt % and 0.05 wt % respectively. The difference between the observed dependence and the T −5 variation predicted in the Raman region for an S-state ion in a perfect lattice is attributed to defects. Measurements in the φ-plane at 4.2 K showed that T 1 was anisotropic with a maximum value atφ=25° about three times greater than the minimum value obtained at φ=55°. The angular positions at which these features occur show a remarkable coincidence with the “acoustic axes of symmetry” of the crystal, which have recently been determined by ultrasonic methods.


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Calcium tungstate suspension was prepared with natrium tungstate and calcium nitrate as the starting materials and polyglycol 200 as the surfactant, and then calcium tungstate nanocrystals were obtained after heat-treatment at 100℃.X-ray diffraction analysis, infrared scattering spectroscopy analysis and transm ission electron microscopy observation indicate that the nicely crystallized calcium tungstate nanocrystals are well dispersed with no aggregation. PEG 200 plays an important role in the dispersal of CaWO4 nanocrystals. When being excited at 265nm, the photolum inescent spectrum of calcium tungstate exhibits the luminous peak in blue band.


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CaWO₄ nanocrystals with average diameters of 20-30 nm and nanorods with mean lengths of 600-1000 nm were controllably synthesized through a facile microemulsion-mediated hydrothermal procedure. And the factors affecting the morphologies of the products, such as the molar ratio ( w) between water and CTAB, the reaction temperature and the concentration of the reactants, were studied and discussed. With the increase of the w value, the diameter of the as-synthesized products increased gradually, except in the case of w=10 where nanorods were formed. With the temperature increasing, the morphologies of the products changed from nanocrystals to nanorods, and finally to nanocrystals again. However, the concentration of the reactants exhibited no obvious influence on the shape and size of the CaWO₄ product. A possible mechanism is proposed for the selective formation of the different morphologies. The photoluminescent properties of the CaWO₄ nanocrystals are also reported. All the products of CaWO₄ with different morphologies exhibited the only green peak at 435 nm with an excitation wavelength at 238 nm.


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Tungsten panoramic collimator is constructed with two tungsten alloy shields designed to provide a 30 degree panoramic radiation beam. The tungsten alloy shields are encased with stainless steel and totally sealed by argon arc welding.Tungsten panoramic collimator can be easily attached to the guide tube exposure head of radiography camera with a thumb screw.

• When an exposure is taken with the collimator attached to the exposure head of the gamma camera guide tube, the radiation beam will have a 30 degree solid angle all around for panoramic exposures.
• The primary radiation beam intensity in other areas will be reduced to 5% with the collimator.
• At a source to film distance (SFD) of 50 cm, the beam will cover a width of a 27 cm.
• Overall size : 44 mm dia x 82 mm long.
• Weight : 1kg.

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