Volume 101, Issue 7

Electrochemistry of U(VI)/U(IV) couple in 1 M H 2 SO 4 was studied on bare and SWCNT modified gold (Au) electrodes by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The gold electrode modified with single-walled carbon nanotubes (SWCNTs-Au) was characterized by scanning electron microscopy (SEM). Electrocatalysis of U(VI)/U(IV) redox reaction was observed on SWCNT-Au. The lower charge transfer resistance at SWCNT-Au promoted the rate of electron transfer reaction of U(VI)/U(IV) couple. These results are interesting to develop electroanalytical methodologies for uranium determination using SWCNT modified electrodes. To the best of our knowledge, this is the first study on the electrocatalysis of uranium on SWCNT modified electrode.

The aim of the work was to determine 241 Pu activities in different components (water, plankton and fish) of the southern Baltic Sea ecosystem. Measurement of 241 Pu in the samples was done indirectly by determining the increment in 241 Am from the decay of the β -emitting 241 Pu in samples collected 10–15 years after the Chernobyl accident. Enhanced levels of 241 Pu were observed in all analyzed Baltic samples. The highest 241 Pu concentrations in fish were found in Perciformes : benthic round goby ( 0.863 ± 0.066 mBq/g ww ) and pelagic perch ( 0.666 ± 0.001 mBq/g ww ). Plutonium is also non-uniformly distributed in the organs and tissues of the analyzed fish; especially pelagic herring and cod as well as benthic flounder. Most of 241 Pu in flounder, herring and cod is located in soft tissues, especially digestive organs (stomach, intestine, liver). The annual individual effective doses calculated on the basis of 241 Pu concentrations in fish indicated that the impact of the consumption of 241 Pu containing Baltic fish on the annual effective dose for a statistical inhabitant of Poland was very small.

Acid-base batch titration data up to 75 ºC were used to constrain a temperature-dependent 1-p K basic Stern model of the surface protonation reactions of goethite. Experimental data for the temperature dependence of pH PZC (as determined using the two-term Van't Hoff extrapolation) yielded a negative value of −44.9 kJ/mol for the surface protonation enthalpy, and therefore a shift of the zero point of charge towards lower pH values with increasing temperature. Batch titrations at selenate concentrations of between 10 and 100 μM showed an increased degree of adsorption in the acidic pH range, which appeared to be sensitive to the ionic strength of the solution. The selenate adsorption edges shifted towards more acidic pH values with increasing temperature. A 1-p K charge distribution multi-site surface complexation (CD-MUSIC) model was applied, assuming the formation of an outer-spheric surface complex together with an inner-spheric one, in agreement with published spectroscopic information. The temperature behaviour of the intrinsic equilibrium constants were well represented by a linear Van't Hoff log K vs . 1/ T plot, from which negative enthalpy values could be derived for both adsorption reactions. The adsorption of the selenate was therefore exothermic and became weaker with increasing temperature. The bidentate inner-spheric complex was more sensitive to rises in temperature (−70 kJ/mol), compared to the outer-spheric complex (−36 kJ/mol). The latter ultimately became the dominating adsorption process at the highest temperature studied.

The adsorption interactions of thallium and its compounds with gold and quartz surfaces were investigated. Carrier-free amounts of thallium were produced in nuclear fusion reactions of alpha particles with thick gold targets. The method chosen for the studies was gas thermochromatography and varying the redox potential of the carrier gases. It was observed that thallium is extremely sensitive to trace amounts of oxygen and water, and can even be oxidized by the hydroxyl groups located on the quartz surface. The experiments on a quartz surface with O 2 , He, H 2 gas in addition with water revealed the formation and deposition of only one thallium species – TlOH. The adsorption enthalpy was determined to be Δ H SiO 2 ads (TlOH) = −134 ± 5 kJ mol −1 . A series of experiments using gold as stationary surface and different carrier gases resulted in the detection of two thallium species – metallic Tl (H 2 as carrier gas) and TlOH (O 2 , O 2 +H 2 O and H 2 +H 2 O as pure carrier gas or carrier gas mixture) with Δ H Au ads (Tl) = −270 ± 10 kJ mol − and Δ H Au ads (TlOH) = −146 ± 3 kJ mol −1 . These data demonstrate a weak interaction of TlOH with both quartz and gold surfaces. The data represent important information for the design of future experiments with the heavier homologue of Tl in group 13 of the periodic table – element 113 (E113).

This paper describes the utility of the electrochemical technique for the preparation of a circular planar 204 Tl source required for the calibration of beta surface contamination monitors. The electrolytic cell, the experimental set up used and the process of deposition are described. The factors that influence the electrodeposition of 204 Tl onto the circular copper substrate were investigated and a careful control has been exercised to ensure an optimum deposition of the 204 Tl activity onto the substrate. The morphology of the deposited layer was examined by SEM, AFM and EDS analyses. Sources containing ∼3.7 MBq (∼0.1 mCi) 204 Tl on a copper sheet of 20 mm diameter working area were prepared and housed in a holder. Quality control tests on the leachability, distribution of activity and stability of the source were performed to ensure compliance with regulatory safety requirements.

An attempt has been made to produce no-carrier-added (nca) 97 Ru for the first time from the 12 C-induced reaction on yttrium target. A  nat Y foil of 10 mg/cm 2 thickness was irradiated by 75 MeV 12 C beams for 3.5 h and a thick target yield of 514 kBq/μA h for 97 Ru and 338 kBq/μA h for 95 Tc was achieved. The nca 97 Ru and coproduced nca 95 Tc were then radiochemically separated from the bulk target by liquid–liquid extraction (LLX). Liquid cation exchanger di-(2-ethylhexyl)phosphoric acid (HDEHP), liquid anion exchanger trioctylamine (TOA) were used in this study. The technique offers efficient chemical separation of the products, resulting in very high separation factors.

In this study, the 166 Ho-triethylene tetramine hexa (methylene phosphonic acid) ( 166 Ho-TTHMP) complex was prepared as a bone palliation agent. The complex was successfully prepared using an in-house synthesized TTHMP ligand and [ 166 Ho]HoCl 3 . Ho-166 chloride was obtained by thermal neutron irradiation (1×10 13  n cm −2 s −1 ) of natural Ho(NO 3 ) 3 samples, followed by radiolabeling and stability studies. Biodistribution studies were also performed in wild type rats. The complex was prepared with the specific activity of 3–5 GBq/mg and a high radiochemical purity > 99%, (checked by ITLC). The 166 Ho-TTHMP complex was stable in the final preparation and in the presence of human serum (> 90%) up to 72 h. The biodistribution of 166 Ho-TTHMP in wild-type rats demonstrated significant bone uptake compared to 166 HoCl 3 up to 48 h. SPECT imaging of the radiolabeled compound was demonstrated to be in complete accordance with the biodistribution data. The major uptake was observed for long bones including thigh bones as well as skull and also knee and vertebrae. Primary properties of 166 Ho-TTHMP demonstrate that this new therapeutic agent can be a good choice for metastatic bone pains.

The gamma radiation-induced degradation of environmental pollutant methoxychlor in water was investigated. A  60 Co gamma radiation source with a dose rate of 372 Gy h −1 was used for gamma irradiation of 1 mg L −1 and 10 mg L −1 methoxychlor in water with a varied absorbed dose of 1–5 kGy. A single step clean up and pre-concentration procedure based on solid phase micro-extraction was optimized. The extent of radiolytic degradation was monitored by reversed phase HPLC-UV and GC-ECD. The trace and ultra trace level degradation products were identified using GC-MS-SPME by comparing their mass spectra with the NIST 98 m mass spectral library. Most of the generated products for 4 kGy dose are substituted chlorophenols. The reaction pathways of these substituted chlorophenols and benzophenone formation are also proposed. However, generated chlorophenols disappeared along with methoxychlor for an absorbed dose of 5 kGy. The attained degradation of methoxychlor is ∼ 95% that reflects the potential use of ionization radiation for wastewater treatment.

Twenty-nine groundwater samples, collected from Wadi Nu'man wells, were analyzed for natural radioactivity to check for compliance with the national guideline values. Gross α and gross β screening, in addition to radon ( 222 Rn) measurements, were performed for all samples. Samples of gross activity levels exceeding the national guideline values set out for drinking water were subjected to further investigation for radium and uranium isotopes using liquid scintillation counting and α -spectrometry, respectively. The results showed that the anomalous source was natural uranium. The water contains high concentrations of 222 Rn and considerable levels of natural uranium. The 222 Rn concentration ranged from 10–100 Bq/L with an average value of about 40 Bq/L. The uranium concentration, in samples of gross activity levels exceeding the national guideline value, ranged from 9 to 55 μg/L. The levels of 226 Ra and 228 Ra were below the detection limit of the counting system in all samples. The variation in the 222 Rn and uranium concentrations was found to be linked with the local lithology. The higher values were recorded in the wells of Nu'man complex aquifer, where the predominating mineral is foliated monzonite. Recommendations and advices for water management to reduce radiation exposure to users are presented.