Viliam Múčka

Energy transfer processes in PbWO4 luminescence

Abstract X-ray-excited luminescence and time-resolved UV-excited photoluminescence were employed to evidence energy transfer processes between two main emission components in PbWO 4 scintillating single crystals. It was found that energy transfer from the blue to green emission centres occurs via free-charge carriers above 150 K. This process causes a redistribution of the emitted energy in favour of the green emission component. At the same time, this process leads to the appearance of rather slow recombination decay components, mainly in the green emission component decay, which slow down the scintillator response of the PbWO 4 single crystal.

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.

Hydrogen peroxide decomposition on NiOBi2O3 mixed oxides before and after their irradiation

Abstract Some physico-chemical and catalytic properties of NiO-Bi 2 0 3 catalysts containing various amounts of components in the range 0–100 wt% of one component have been studied before and after 1-MGy-γ irradiation in air or in water using the hydrogen peroxide decomposition as a test reaction. Irradiation, when performed in water, led to a decrease in catalytic activity but did not lead to modification of the mutual influence of both components of the catalysts. The annealing of radiation effects was observed at temperatures above 50°C.

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.

Catalytic activity of nickel-zinc mixed oxides prepared in different ways and the influence of ionizing radiation

Abstract The catalytic activities and some physico-chemical properties of NiO-ZnO catalysts prepared by precipitation of mixtures of carbonates and nitrates of both metals and subsequent calcination have been tested before and after irradiation, using the decomposition of hydrogen peroxide as a test reaction. A mutual influence of both oxides and their sensitivities to ionizing radiation have been proved.

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.

Catalytic and physico-chemical properties of CuOBi2O3 mixed oxides before and after their irradiation

Abstract Some physico-chemical and catalytic properties of two-component CuOBi 2 O 3 catalysts containing various ratios of both components in the range 0–100 wt% of one component have been tested before and after γ- and electron-irradiation, using the decomposition of hydrogen peroxide as a test reaction. Irradiation led to modification of mutual influence of both components in the system accompanied by creation of radiolytically induced catalytic sites.