Study of 99mTc absorption on micro-sized ion exchange resins to achieve high activity for SPECT.

In single-photon emission computed tomography (SPECT), a micro-sized 99mTc source is routinely used for performance measurement, geometry calibration, and system matrix generation. Therefore, a micro-sized source is critical in nuclear instrument production and quality control. Standard methods can only produce a point source with a large size and low total activity, as they are limited by the concentration of the 99mTc solution. The absorption of 99mTc on ion exchange resins has been used; however, few studies have quantitatively evaluated the absorption process and optimized the source activity. This paper proposes a procedure for producing a micro-sized 99mTc resin source with a super-high concentration, as well as a method for the fast measurement of the point source time-activity curve (TAC). Experiments on two resin point sources with diameters of 0.681 mm and 0.326 mm were carried out. Two semi-empirical models, including the first kinetic model and the pseudo-second-order rate equation model, were used to fit TACs. The results show the first kinetic model fit better, which suggests an acquisition time of 2-4 h is needed for optimization. The verification experiment demonstrates a resin point source with a diameter of 0.35 mm and total activity of 10.6 mCi (i.e., 59.1 Ci/mL concentration) was produced.

Fabrication of rGO and g-C3N4 co-modified TiO2 nanotube arrays photoelectrodes with enhanced photocatalytic performance.

To enhance the photocatalytic performance of titanium dioxide (TiO2) and reduce the photocorrosion of graphitic carbon nitride (g-C3N4), two-dimensional (2D) reduced graphene oxide (rGO) and g-C3N4 co-modified three-dimensional (3D) TiO2 nanotube arrays (rGO@g-C3N4/TNAs) photoelectrodes were fabricated by the combination of impregnation, annealing and electrochemical cathode deposition. The micromorphology and microstructure were observed by SEM and TEM. The crystalline structure and element composition were characterized by XRD, XPS and Raman spectra. The optical and photo-electrochemical properties were analyzed by UV-vis DRS, open circuit potential and photocurrent density. Results indicated that g-C3N4 and rGO were successfully loaded on the surface of the TNAs photoelectrodes and formed rGO@g-C3N4/TNAs heterostructure. The photocatalytic activity of the photoelectrodes was evaluated by the degradation rate of tetracycline hydrochloride (TC) under xenon lamp irradiation. The introduction of g-C3N4 and rGO reduced the band gap of TNAs photoelectrodes and promoted the separation of photo-induced electron-hole pairs. The rGO@g-C3N4/TNAs photoelectrodes exhibited higher photo-electrochemical properties and photocatalytic activity. The removal rate of TC by rGO@g-C3N4/TNAs photoelectrodes could reach 90% under 120 min photo-degradation and reaction kinetic constant was 2.38 times that of TNAs photoelectrodes. The active radicals capture and ESR experiments results showed that O2- radical and OH radical played the major role in photocatalytic degradation of TC. The possible photocatalytic mechanism of rGO@g-C3N4/TNAs photoelectrodes was presented.

Tunable Luminescence in Sr2MgSi2O7:Tb3+, Eu3+Phosphors Based on Energy Transfer.

A series of Tb3+, Eu3+-doped Sr2MgSi2O7 (SMSO) phosphors were synthesized by high temperature solid-state reaction. X-ray diffraction (XRD) patterns, Rietveld refinement, photoluminescence spectra (PL), and luminescence decay curves were utilized to characterize each sample's properties. Intense green emission due to Tb3+ 5D4→7F5 transition was observed in the Tb3+ single-doped SMSO sample, and the corresponding concentration quenching mechanism was demonstrated to be a diople-diople interaction. A wide overlap between Tb3+ emission and Eu3+ excitationspectraresults in energy transfer from Tb3+ to Eu3+. This has been demonstrated by the emission spectra and decay curves of Tb3+ in SMSO:Tb3+, Eu3+ phosphors. Energy transfer mechanism was determined to be a quadrupole-quadrupole interaction. And critical distance of energy transfer from Tb3+ to Eu3+ ions is calculated to be 6.7 Šon the basis of concentration quenching method. Moreover, white light emission was generated via adjusting concentration ratio of Tb3+ and Eu3+ in SMSO:Tb3+, Eu3+ phosphors. All the results indicate that SMSO:Tb3+, Eu3+ is a promising single-component white light emitting phosphor.