Band 102, Heft 8

Excitation functions, thin- and thick-target yields for the 181−186g Re and 187 W radionuclides were measured by the activation stacked-foil thecnique on natural tungsten foils for deuteron energies up to 18.0 MeV. These cross sections were validated by comparing the experimental results for thick-target yields with those calculated by integration of the thin-target yields. It was found that the maximum 186g Re content by irradiation of natural tungsten is about 55%, a higher value compared with the one found for proton beam, but not sufficient to use natural tungsten for medical purposes yet. Thus, in order to have a higher specific activity A S of 186g Re, the use of enriched 186 W target is necessary. Therefore the irradiation of a thick target of enriched 186 W by accelerated deuterons was studied and the results for the production of 186g Re were compared with those obtained from the irradiation of the same target by accelerated protons. It was found that the deuteron irradiation is preferable for three reasons: larger yield, less contamination by tantalum radioisotopes and smaller required amount of the target, which simplify the separation of the 186g Re from the target itself.

A method is proposed for production of polonium-210 via the 209 Bi( α , 3 n ) 210 At nuclear reaction. Bombardment of a bismuth-209 target was performed with a 37 MeV alpha-particle beam that leads to the production of astatine-210 ( T 1/2  = 8.1 h), which decays to polonium-210. It is purified from the bismuth target matrix by employing liquid–liquid extraction using tributyl phosphate (TBP) in para -xylene from 7 M hydrochloric acid. Back extraction of polonium-210 was performed by 9 M nitric acid. This method allows to purify a tracer amount of Po-210 (2.6 · 10 – 13  mol) from macroscopic amount of Bi (2.8 · 10 – 2  mol).

Controlled-potential coulometry is an assay method for determining the quantity of a given element from the measurement of a quantity of electricity. This method has the advantage of not being related to a chemical standard, having an extremely high trueness and reproducibility, and using low sample amounts. Nowadays, equipments intended to carry out coulometry with high trueness (typically uncertainties close to 0.1%) is seldom encountered. In order to arrive to such low uncertainties, the whole process, from the preparation of the sample test to thestorage of the material had to be refined. The qualification of the method was carried out thanks to the use of EQRAIN standard solutions. The coulometric proportioning of plutonium coming from pure solutions (without interfering elements) was extended to the proportioning of plutonium in the presence of uranium, which makes the technique not only a method of choice for standard solution certification but also appropriate for carrying out precise analyses assessments of different processes used in nuclear medium.

Understanding the effect of soil parameters (pH, Eh and organic and inorganic ligands availability) on uranium mobility under different geochemical conditions is fundamental for reliable prediction of its behaviour and fate in the environment. In this study, the impact of total and available phosphorus content, humus and acidity of Serbian agricultural soils on the content of total and available uranium were evaluated by Response Surface Methodology (RSM), second order polynomial regression models (SOPs) and artificial neural networks (ANNs). The performance of ANNs was compared with the performance of SOPs and experimental results. SOPs showed high coefficients of determination (0.785–0.956), while ANN model performed high prediction accuracy: 0.8893–0.904. According to the results, total and available uranium content in the soil were mostly affected by pH, statistically significant at p  < 0.05 level. For the same responses the total phosphorus was found to be also very influential, statistically significant at p  < 0.05 and p  < 0.10 levels. The impact of available phosphourus and humus was much more influential on total and available uranium content, compared to total phosphorus content. Proposed chemometric approach will be very helpful in preserving the natural resources and practical application for risk assessment modeling of uranium environmental pathways.

The solubility of Ba(SeO 4 , SO 4 ) precipitates was determined as a function of the BaSeO 4 mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/steady state conditions in this system are reached in ≤ 65 days. Pitzer's ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with log  10 [Ba] ranging from − 3.6 to −5.9 mol kg – 1 , log  10 [SeO 4 ] ranging from − 3.6 to −5.2 mol kg – 1 , and log  10 [SO 4 ] ranging from − 4.0 to −5.3 mol kg – 1 can be explained with the formation of an ideal BaSeO 4 solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO 4 (s) (log  10 K ○ sp  =− 9.5 instead of − 10.05 for barite) that controls the sulfate concentrations. In these experiments the BaSO 4 component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO 4 solid solution phase and less-crystalline BaSO 4 (s) phase are in equilibrium with each other in the entire range of BaSeO 4 mole fractions investigated in this study.

The suitability of different porous materials (stainless steel, VYCOR ® glass, Al 2 O 3 and PEEK) for use as confining filters in diffusion experiments was evaluated by measuring the effective diffusion coefficients ( D e ) of neutral (HTO) and ionic solutes (Na + , Cs + , Sr 2+ , Cl – , SeO 4 2− ) in the materials in through-diffusion experiments. For stainless steel filters, the D e values of the target solutes correlated satisfactorily with their bulk diffusion coefficient in water ( D w ); thus, the diffusion process in the stainless steel filters was primarily controlled by the diffusivity of the solvated ions. For the remaining materials, the D e and D w values were also correlated for the target solutes, and the geometric factors were in the sequence: VYCOR ® glass < Al 2 O 3 < PEEK. Stainless steel and VYCOR ® glass were the most appropriate materials because of their high D e values, but a specific interaction of caesium with VYCOR ® glass was hypothesised because the D e values obtained for this solute were slightly higher than expected.

Gamma radiolytic degradation of azinophos-methyl was studied in water and methanol separately, using 60 Co as a radiation source under varied experimental conditions. Solution of azinophos-methyl was prepared in pure methanol at concentration of 50  μ g ml −1 , irradiated at gamma dose of 1 to 7 kGy and high performance liquid chromatography (HPLC) coupled with diode array detector was used to monitor the extent of degradation along with numbers of degradation products. At dose of 7 kGy ≥ 99% of azinophos-methyl was degraded. The degradation occurred by interaction of CH 3 O . and H . radicals generated by the radiolysis of high purity methanol while in water by . OH radical. The degradation in water was increased by 30% than in methanol due the high oxidation potential of . OH while keeping the gamma ray dose constant at 3 kGy. The generated degradation products were identified using GC-MS and their possible transformation pathways are proposed. It is suggested that use of ionization radiations can be an effective and efficient tool for the removal of organophosphate pesticides in waste water.

An analysis of metallic elements and natural radioactivity in soils collected from two shipyards and their surroundings in Chittagong, Bangladesh is presented. The elemental concentrations of the metals Cr, Mn, Fe, Ni and Cu were obtained by PIXE analysis with a 3 MV Tandem Accelerator, and the radioactivity of 226 Ra, 232 Th and 40 K was determined using HPGe gamma-ray spectrometry. From the mean specific activities of the three radionuclides in soil samples, the radium equivalent activity, the gamma absorbed dose rate, the annual effective dose rate and the external hazard index were calculated. The study was focused on investigation of soil contamination via shipbreaking activities, if any. The somewhat higher contents of Cr, Mn, Fe, Ni and Cu in soil samples of shipyards, as compared to other locations, seem to be caused by the shipbreaking activities. The specific radioactivities as well as radium equivalent activity in soils of shipyards are also higher and thus possibly an indirect result of shipbreaking activities.

238 U, 234 U, 226 Ra, 210 Pb and 210 Po were measured in some jurak and mehassel samples collected from the local market. Jurak is a paste mixture composed of 30% tobacco, 50% molasses and 20% spices and minced fruits. Mehassel is a local trade-name of a paste mixture of unknown ratios of tobacco to spices and minced fruits. Both jurak and mehassel are used for smoking by Shisha (a pipe used for smoking and has a water filter). Just for comparison, these radionuclides were measured in some cigarette tobacco samples. In cigarette tobacco samples, the average activity concentrations were 0.32 ± 0.10, 0.51 ± 0.11, 3.6 ± 1.0, 16.1 ± 2.4 and 15.8 ± 2.2 Bq/kg for 238 U, 234 U, 226 Ra, 210 Pb and 210 Po, respectively. These values for the same isotopes were 1.01 ± 0.25, 1.04 ± 0.27, 1.2 ± 0.4, 4.4 ± 1.0 and 4.2 ± 0.9 Bq/kg in jurak samples and 0.17 ± 0.07, 0.24 ± 0.08, 1.8 ± 0.7, 7.5 ± 1.7 and 7.0 ± 1.6 Bq/kg in mehassel samples, respectively. Generally, the mean values of the results indicated that, except for uranium in jurak, the activity concentration for all the analyzed radionuclides in the different samples followed the sequence: 210 Po ≈ 210 Pb > 226 Ra ≫ 234 U > 238 U, whereas for each radionuclide, its activity concentration followed the sequence: cigarette tobacco > mehassel > jurak. Molasses contributed to the enhanced uranium content in jurak samples. The obtained results are discussed in detail.

The activity concentrations of 40 K, 226 Ra and 232 Th in the commonly used building materials collected from Xiangyang were measured using NaI (Tl) gamma spectrometer. The radioactivity values of 40 K, 226 Ra and 232 Th in the studied samples ranged from 130.5 to 1006.3, 8.4 to 164.0, and 8.7 to 145.6 Bq kg – 1 , respectively. The concentrations of these radionuclides have been compared with the typical published world values. Radium equivalent activity, external and internal hazard indexes, external and internal exposure indexes, indoor air absorbed dose rate and annual effective dose rate have been calculated to assess the potential radiological hazard associated with natural radionuclides in the studied materials. The calculated values of all the assessed indices in the analyzed building materials except for fly ash are below the internationally accepted limits indicating that these building materials can be safely used in dwellings construction and do not lead to any significant radiation exposure to occupants. Nevertheless, the annual effective dose rate values of all fly ash samples, external and internal hazard indexes values in most fly ash samples exceed the recommended values. It is, therefore, desirable to regularly monitor the natural radioactivity level of the building materials products made from fly ash.