Calcium tungstate phosphors activated by the Ln³⁺ ions (Ln=Pr, Nd, Tb, Yb) were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy (SEM), X-ray powders diffraction (XRD) and infrared spectra (FT-IR). The samples were found to show luminescence properties (down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb³⁺/Yb³⁺showed green DC and UC luminescence characteristic of Tb(III) ion in the range of 470-660 nm, cor-responding to the ⁵D₄→⁷F_6,5,4,3,2 electronic transition. CaWO₄ doped with Pr³⁺/Yb³⁺showed week blue, green and red (DC and UC) luminescence of Pr(III) ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the ³P₁→³H_4,5,6, ³P₀→³H_4,5,6, ³P₁→³F₂ and ³P₀→³F₂ transitions, respectively. CaWO₄ doped with Nd³⁺/Yb³⁺phosphor emitted orange UC luminescence at 450-690 nm (²P_3/2→⁴I_15/2, ⁴G_7/2→⁴I_{9/2,11/2,13/2}) and strong near-infrared UC luminescence at 720-900 nm (⁴F_7/2+⁴S_3/2→⁴I_9/2, ⁴F_5/2+²H_3/2→⁴I_9/2, ⁴F_3/2→⁴I_9/2) which is the characteristic of Nd(III) ion.

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Beam collimators, which are usually made of tungsten alloy shielding, including linear accelerators and tungsten multi-leaf collimators and so on. Beam collimators are 'beam direction' devices used in the X-ray tube housing, along with an arrangement of mirrors and lights, in such a way that the light and X-ray fields match each other. They are made of lead shutters which completely absorb the photons, and thus reduce patient dose as well as focus the radiation accordingly to the area of interest. They allow different projections of X-ray fields.
 
In linear accelerators (linac), the primary collimator may be constructed of depleted uranium (DU) as this material is approximately 1.6 times more dense than lead. The secondary motorised collimators which greater define the beam shape are constructed of tungsten. Multi-leaf collimators (MLCs) which are now in widespread use in medical linacs consist of two collimator banks of thin tungsten 'leaves' with each bank consisting of 40 to 80 leaves (so a total of 80 to 160 leaves). This allows each tungsten leaf to move independently under computer control. MLCs allow even more diverse field shapes to be created which can shield organs at risk whilst allowing the complex shape of the tumour bed to be irradiated to allow maximum cell kill.

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Due to tungsten alloy has high density, excellent radiation attenuation properties, and environmental friendly, it is widely used in medical imaging technology. Medical imaging technology has tended to become more integrated over the past decade. While combined Positron Emission Tomography and Magnetic Resonance Imaging (PET/MRI) is rapidly gaining popularity, no commercial systems for combining the complementary functional imaging techniques of Single Photon Emission Computed Tomography (SPECT) and MRI have been developed. This is mainly due to the physical space constraint, magnetic incompatibility of collimators and the required rotation mechanism inside the MRI bore. Some approaches investigated this integration but no one focused on the development of preclinical SPECT systems and their integration with pre-clinical MRI without compromising image quality and taking into account the MR-compatibility of the collimator material. This study investigates eddy currents in the collimator due to the magnetic field gradients, for different resistivities of tungsten, for small animal SPECT/MRI. Collimator resistivity can be tuned nowadays through tungsten additive.

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Tungsten polymer Shielding’s density approaching twice that of high density Lead Blankets of similar thickness. Highly flexible and can be molded/formed into any shape. Often competitively priced to lead alternatives.

The advantages of tungsten polymer shielding system:

• Provides approx. 75% Attenuation as compared to solid lead
• Attenuation of 175% compared to a high density lead blanket
• Priced competitively to lead for many applications
• Available as a blanket, ribbon wrap or molded shapes; flexible or rigid
• Cut materials to fit without needing to seal edges - no residue
• Included fasteners, grommets, locking devices, etc., as required
• Improved fit-up --- molded applications typically will yield much higher reduction factors - less weight with same impact
• Tested to 550°F/288°C

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