Milan Pospíšil

Electron beam degradation of polychlorinated biphenyls

Abstract A gradual degradation of polychlorinated biphenyls (PCBs) was found under the influence of accelerated electrons (4.5 MeV) absorbed in alkaline 2-propanol solutions containing 0.3–1.0 vol.% of PCBs. A degree of dechlorination grows with increasing dose of irradiation from 2 to 100 kGy. The inhibiting effects of acetone as well as of oxygen were observed.

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.

Radiolytic dechlorination of PCBs in presence of active carbon, solid oxides, bentonite and zeolite

Abstract The influence of various solids on the radiation dechlorination of polychlorinated biphenyls using electron beam radiation was investigated. Some of the promoters exhibited a positive effect on the radiation dechlorination with a maximum at a determined amount of solids. Some of them exhibited a pronounced negative effect in dechlorination reaction.

Radiation degradation of polychlorinated biphenyls

Abstract Gradual dechlorination of the polychlorinated biphenyls (PCBs) in alkaline solutions in 2-propanol under the effect of high energy electrons (4.5 MeV) produced by electron accelerator has been studied using a flow-through apparatus of the volume of about 50 L. The dependence of both relative radiation chemical yield and the dechlorination degree on the initial concentration of OH − ions or PCBs, absorbed dose as well as on dose rate has been investigated.

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.

Radiation dechlorination of PCE in aqueous solutions under various conditions

Abstract The radiation dechlorination of tetrachloroethylene (PCE) caused by both γ - and EB (accelerated electrons)-irradiation in aqueous solutions, containing oxygen, nitrous oxide, HCO 3 − - or NO 3 − -ions, was studied. The promoting and inhibiting effects of the two firstly and lastly mentioned species were observed, respectively. The influence of pH on this process was also investigated.

Dechlorination of chloroform in aqueous solutions influenced by nitrate ions and hydrocarbonate ions

Abstract The dechlorination of aqueous solutions of chloroform with γ -radiation was studied in the presence of various concentrations of HCO 3 − - and NO 3 − -ions. The dechlorination was found to be positively influenced by HCO 3 − -ions and a pronounced negative influence of the NO 3 − -ions was observed.

Effects of genesis and ionizing radiation on the physicochemical properties and reduction reactivity of NiO-ZnO mixed oxides with hydrogen

Abstract The physicochemical properties and hydrogen reduction reactivity have been studied for two series of nickel and zinc mixed oxides of various compositions; the two series differ in the genesis of both their major components. It was found that the different absolute values of the physicochemical parameters of the mixed oxides vary with their compositions and depend on the origin of the major components. The changes in the properties of the samples in both series can be correlated with their reduction reactivity as seen by isothermal thermogravimetry in the temperature range 260–500 ° C. Only the series containing zinc oxide in interaction with strongly non-stoichiometric nickel oxide appears to be sensitive to pre-irradiation by γ rays (328 kGy and 3.7 MGy doses) and accelerated electrons (500 kGy dose). The negative effect (a decrease in the rate of reduction) in the region of excess nickel oxide reverses to a positive one (acceleration of reduction) with increasing zinc oxide content, forming a separate phase of the mixed system.

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.

Reduction reactivity of CuO-Cr2O3 mixed oxides with hydrogen and the effect of gamma pre-irradiation

Abstract The physico-chemical properties and parameters of CuO-Cr 2 O 3 mixed oxides as well as their reactivity toward reduction with hydrogen have been investigated by means of various methods (X-ray analysis, electron spectroscopy for chemical analysis (ESCA), DTA, IR spectroscopy and scanning electron microscopy). A series of mixed oxides of various compositions in the range 0–100% of each component were prepared by calcinating the mass of coprecipitated basic carbonates in air. The reduction kinetics were studied by isothermal thermogravimetry in the temperature range 180–470 ° C. The effect of the origin of the oxides on the reactivity of the oxide system during its hydrogen reduction was proved by comparing its properties with those of a previously studied series of analogous mixed oxides, which were prepared from different precursors. The pre-irradiation of the system by 60 Co γ radiation results in a positive kinetic effect (an increase in the reduction rate) if the lowest dose applied is 2.57 × 10 6 Gy. The magnitude of the radiation effect is greatly dependent on the composition of the mixed oxides.