Manuel Garcia

Preparation of CaSO4:Dy by precipitation method to gamma radiation dosimetry

This paper presents the results of the preparation and characterization of dysprosium-doped calcium sulfate (CaSO(4):Dy) phosphor, which was obtained by homogeneous precipitation from calcium acetate Ca(CH(3)COO(-))(2). Structural and morphological characteristics were studied using a scanning electronic microscope (SEM). The structure of all compounds was determined by X-ray diffraction method too. Thermoluminescence (TL) emission properties of CaSO(4):Dy under gamma radiation effects were studied. This phosphor powder presented a TL glow curve with two peaks (Tmax) centered at around of 180 and 300 degrees C, respectively. The TL response of CaSO(4):Dy as a function of gamma absorbed dose was linear in a wide range. Both emission and excitation spectra were also obtained. Results showed that this new preparation method of CaSO(4):Dy TL phosphor is less expensive, cleaner and safer than the conventional preparation method.

Donor-Acceptor Tubular Nanoaggregates of Cyclic Oligothiophenes. A Theoretical Study

The geometries of neutral, monooxidized, and monoreduced donor-acceptor tubular aggregates of cyclo[8]thiophene, cyclo[8](3,4-dicyanothiophene), and the corresponding donor-acceptor tubular nanoaggregates containing up to 4 repeating units were fully optimized at MPWB1K/3-21G* level of theory. The binding energies between macrocycles in neutral donor-acceptor tubular aggregates (77-84 kcal/mol) were found to be much higher compared to donor (43-45 kcal/mol) or acceptor (27-28 kcal/mol) aggregates. The oxidation or the reduction of the donor-acceptor tubular aggregates lead to a decrement in the binding energy. However, the reduction increases the binding in acceptor aggregates and decreases in donor ones, whereas the oxidation causes the opposite effect. In spite of a decrease in the binding energy in donor-acceptor aggregates in oxidized or reduced states, they remain the most thermodynamically stable formations. Donor-acceptor aggregates possess the lowest band gap among all studied systems (1.31 eV for the tetramer) and the photoexcitation of donor-acceptor aggregates results in almost complete electron transfer from donor to acceptor fragment, thus showing a very strong charge separation in the excited-state, which is highly desirable in materials with potential application in photovoltaic devices. Polaron cations are localized at donor fragments, whereas polaron anions are located at acceptor units.

Green stimulated luminescence of ZrO2 + PTFE to UV radiation dosimetry

Abstract The use of optically stimulated luminescence (OSL) as a method for the determination of environmental radiation absorbed dose using solid state materials has become the main interest of the most great research centers. The aim of this work is to study some dosimetric characteristics of ZrO2 to be used as a UVR dosemeter by using the OSL method. The most attractive characteristic of ZrO2 is its very high intrinsic sensitivity to UV radiation. Optical characteristics of ZrO2 were also studied. OSL typical decay was obtained. OSL response of ZrO2 samples as a function of irradiation time was linear in the range of 30–1000 s. Experimental results showed that ZrO2 exhibit attractive characteristics which make it suitable for UV dosimetry applications.