Václav Čuba

Radiation-induced preparation of pure and Ce-doped lutetium aluminium garnet and its luminescent properties

Radiation-induced preparation of pure or doped lutetium aluminium garnet Lu3Al5O12 (LuAG) is reported as a simple and robust process, which is easy to control. Irradiation of an aqueous solution containing formate anions and soluble salts of both metal ions by ionizing radiation or UV light leads to precipitation of an amorphous solid phase. Subsequent calcination in the interval 850–1200 °C results in the crystallization of the LuAG with a well developed structure. Depending on the calcination temperature, the particle size ranges from 20 to 60 nm; the prepared LuAG nanopowder was also found to be easily compactable. The manufactured Ce-doped LuAG features intensive luminescence corresponding to Ce3+ 5d–4f transitions at 510 nm and its photoluminescence excitation spectrum comprises two Ce3+ 4f–5d1, 5d2 bands at 450 and 347 nm, respectively. The decay times of Ce3+ emission in nanopowders were substantially influenced by the nanomorphological character of the prepared material. Due to its high density, chemical stability, non-toxic character and excellent scintillation efficiency, the application of Ce-doped LuAG nanopowder in photodynamic therapy and in optical ceramics preparation is suggested.

Preparation and luminescence properties of ZnO:Ga – polystyrene composite scintillator

Highly luminescent ZnO:Ga-polystyrene composite (ZnO:Ga-PS) with ultrafast subnanosecond decay was prepared by homogeneous embedding the ZnO:Ga scintillating powder into the scintillating organic matrix. The powder was prepared by photo-induced precipitation with subsequent calcination in air and Ar/H2 atmospheres. The composite was subsequently prepared by mixing the ZnO:Ga powder into the polystyrene (10 wt% fraction of ZnO:Ga) and press compacted to the 1 mm thick pellet. Luminescent spectral and kinetic characteristics of ZnO:Ga were preserved. Radioluminescence spectra corresponded purely to the ZnO:Ga scintillating phase and emission of polystyrene at 300-350 nm was absent. These features suggest the presence of non-radiative energy transfer from polystyrene host towards the ZnO:Ga scintillating phase which is confirmed by the measurement of X-ray excited scintillation decay with picosecond time resolution. It shows an ultrafast rise time below the time resolution of the experiment (18 ps) and a single-exponential decay with the decay time around 500 ps.

Radiation formation of colloidal silver particles in aqueous systems.

This paper reports on the formation of silver nanoparticles initiated by gamma and UV radiation in various aqueous solutions. Inorganic precursors were used for radiation and/or photochemical reduction of Ag(+) ions to a metallic form. The influence of various parameters on the nucleation and formation of colloid particles was studied. Attention was also focused on the composition of the irradiated solution. Aliphatic alcohols were used as scavengers of OH radicals and other oxidizing species. The influence of the stabilizers on the formation and stability of the nanoparticles was studied.

Products of radiation removal of lead from aqueous solutions.

The influence of typical *OH radical scavengers as potassium formate and isopropanol on the radiation-induced removal of lead was individually studied. The lead can be completely removed from aqueous solutions containing 1x10(-2) mol/L of formate already at the dose of 2.5 kGy. With increasing concentration of formate (5x10(-5)-1x10(-2) mol/L) increases the amount of Pb(formate)(+) species in the solution before irradiation. The radiation product is metallic lead at low concentration of formate to PbCO(3) at higher concentration of scavenger. In the system with 10% isopropanol dominates the species Pb(2+) and the product of radiation reduction is then metallic lead.

Influence of various scavengers of •OH radicals on the radiation sensitivity of yeast and bacteria

Abstract Purpose: To quantitatively investigate the influence of various •OH (hydroxyl radical) scavengers on the radiation sensitivity of yeast and bacteria, particularly to define the relationship between the protective effect of a scavenger and its •OH scavenging efficiency. Materials and methods: In order to study the protective effect of •OH scavengers we used various concentrations of four scavengers (methanol, potassium formate, ethanol and ascorbic acid) in isotonic salt solutions. These solutions containing live yeast (Saccharomyces cerevisiae) or bacteria (Escherichia coli) were irradiated with 60Co isotope γ -radiation using two different doses and dose rates. The number of surviving cells was determined prior to and after irradiation both in suspension with and without scavengers. The surviving fractions after irradiation with and without the scavenger were evaluated. Results and conclusions: The main results of the paper were: The surviving fraction increased approximately linearly within the measured interval with increasing concentration of the scavenger. The same dependences were found for the protecting effect depending on the scavenging efficiency. The slopes of these dependences (k) were found to be characteristic for each scavenger. The k value determined the degree in which the scavenging of •OH radicals participated in the protection of living cells. The protective effects of scavengers at the same scavenging efficiency were different and unique for each scavenger. No simple relation was found between the efficiency of scavenger k and the rate constant kOH of the reactions between scavengers and •OH radicals. Our results suggest that the studied scavengers effectively protected yeast and bacteria against ionizing radiation. Although the scavenging of •OH radicals seems to be important for protection of living cells, it is clearly not the only process on which the protection is based.

Thiacalixarenes: radiation stability and Eu/Am extraction in synergistic systems with COSANs

The radiation stability of thiacalixarenes was not studied systematically, yet. This paper focuses on the stability of two thiacalix[4]arene molecules dissolved in 1,2-dichloroethane or cyclohexanone towards irradiation from 60Co source or linear electron accelerator. The determination of thiacalixarene residual concentration using HPLC method was compared with the assessment of the change in the extraction efficiency, i.e. the change of the distribution ratios of americium and europium in solvent extraction experiments with COSAN molecules. Extraction properties of synergistic mixtures containing irradiated and non-irradiated thiacalixarenes were compared. It was shown that irradiation significantly negatively influences extraction properties of the mixtures.

Impact of accelerated electrons on activating process and foaming potential of sludge

Abstract The process of activation is an important part of wastewater treatment technology. It can be affected in many ways, not least by using radiation. The paper describes effects of pre-irradiation of small part of biomass on activated sludge process. It has been shown, that relatively low dose of accelerated electrons can positively affect many parameters of the system.

Degradation of phospholipids under different types of irradiation and varying oxygen saturation

The effects of different types of radiation on the formation of peroxide forms of 2-dioleoyl-sn-glycero-3-phosphocholine were studied under various conditions. For the irradiation, an aqueous solution of small unilamellar vesicles was prepared. Variations in parameters such as the dose rate and molecular oxygen saturation levels were evaluated. Our study suggests that the mechanism of the peroxides formation process remains unchanged under irradiation by accelerated electrons, gamma and accelerated protons. The values of radiation chemical yields of the peroxidic form depend on the type of radiation, dose rate, and the saturation of molecular oxygen. The level of oxygen saturation strongly affects the values of radiation chemical yields as well, as the dissolved oxygen is an important agent participating in peroxidation and it is a source of free radicals during the radiolysis. The values of radiation chemical yields strongly suggest that the mechanism of radiation-induced peroxidation of phosphatidylcholines does not proceed via chain reaction.Graphical Abstract

Determination of the survival of yeast and bacteria under the influence of gamma or UV radiation in the presence of some scavengers of OH radicals

Two new methods for quantitative determination of the role of scavengers of OH radicals in the radiation protection of various microorganisms were studied. The yeast and bacteria were irradiated with gamma or UVC radiations having quite different effect on living cells. Both methods based on the counting of colonies arising from surviving cells proved to be able to describe quantitatively the protective effect of scavengers. The described method may be helpful for study of the radiation protection of cells, radiation stability of DNA or the permeability of the cell membrane.

Radiation and chemical stability of calix[4]arene derivatives as prospective liquid-liquid extractants

Abstract Radiation and chemical stabilities of CMPO-functionalised calix[4]arenes, promising ligands for extraction of actinides and lanthanides, were studied both in solution and in the solid state. A comparison of the results showed that the degradation of ligands under radiolytic conditions proceeds indirectly via interactions with the solvent. The radiation stabilities in chloroform and 1-octanol were systematically studied using model compounds, and the main degradation product under extraction conditions (organic phase/conc. HNO3) was characterised.