Production of <Superscript>41</Superscript>Ar and <Superscript>79</Superscript>Kr gaseous radiotracers for industrial applications

Radiotracers are extensively used in many industries for trouble shooting and optimization of process parameters leading to considerable savings in time and huge economic benefits. In chemical and petrochemical industries different gases and vapours flowing in the conversion reactors play a major role in the final production. Gaseous radiotracers are ideal to study hydrodynamics of gas phases in process vessels. ⁴¹Ar and ⁷⁹Kr are the preferred gaseous radiotracers for such studies. Owing to the increase in demand from Indian industries for gas phase radiotracers, efforts have been made to produce ⁴¹Ar and ⁷⁹Kr indigenously by irradiation of ⁴⁰Ar and enriched ⁷⁸Kr gaseous targets in research reactors. Prequalification of the containers used, safety aspects concerning accidental rupture and mandatory tests necessary for irradiation of gaseous targets in the reactors have been studied. The paper describes some of the important safety aspects involved and the results of trial irradiations on the production of ⁴¹Ar and ⁷⁹Kr radiotracers. Standardization of suitable assay protocols for their regular production and supply for applications in industries is also described.     

Adsorption of <Superscript>125</Superscript>Sb on alumina and titania surfaces

Adsorption of long-lived ¹²⁵Sb radioisotope (T _1/2 = 2.75 y) on alumina (Al₂O₃) and titania (TiO₂) has been studied at different pH. Both the oxides have good adsorption capability for the ¹²⁵Sb radioisotopes but the TiO₂ is much superior. Adsorption kinetics of ¹²⁵Sb radioisotopes on TiO₂ surface and desorption of ¹²⁵Sb radioisotopes from TiO₂ surface in acidic and alkaline media have also been studied. The ¹²⁵Sb-TiO₂ phase has been subjected to γ-irradiation and found to be radiation stable against antimony release.     

<Superscript>226</Superscript>Ra and <Superscript>228</Superscript>Ra determination in environmental samples by alpha-particle spectrometry

A complete methodology for ²²⁶Ra and ²²⁸Ra determination by alpha-particle spectrometry in environmental samples is being applied in our laboratory using ²²⁵Ra as an isotopic tracer. This methodology can be considered highly suitable for the determination of these nuclides when very low absolute limits of detection need to be achieved. The ²²⁶Ra determination can be performed at any time after the isolation of the radium isotopes from the analyzed samples while the ²²⁸Ra determination needs to be carried out at least six months later through the measurement of one of its grand-daughters. The method has been validated by its application to samples with known concentrations of these Ra nuclides, and by comparison with other radiometric methods.     

Production cross section of <Superscript>236</Superscript>Th in the interaction of <Superscript>238</Superscript>U with 60 MeV/u <Superscript>18</Superscript>O ions

The neutron-rich target-like isotope ²³⁶Th has been produced in the ²³⁸U-2p multinucleon transfer reaction between a 60 MeV/u ¹⁸O beam and natural ²³⁸U targets. The activities of thorium were determined after radiochemical separation of Th from the mixture of uranium and reaction products. The ²³⁶Th isotope was identified by the characteristic γ-rays of 642.2, 687.6 and 229.6 keV. The production cross section of ²³⁶Th was determined to be 250±50 μb.     

<Superscript>234</Superscript>U/<Superscript>235</Superscript>U activity ratios as a probe for the <Superscript>238</Superscript>U/<Superscript>235</Superscript>U half-life ratio

High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in ²³⁵U. Besides the ²³⁵U peaks, separate peaks belonging to impurity traces of ²³⁴U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of the half-lives of ²³⁸U and ²³⁵U was determined via the activity ratio of ²³⁴U and ²³⁵U in the materials. As an intermediate link, the ²³⁴U/²³⁸U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting half-life ratio T _1/2(²³⁸U)/T _1/2(²³⁵U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al.     

Low level detection of <Superscript>135</Superscript>Cs and <Superscript>137</Superscript>Cs in environmental samples by ICP-MS

The measurement of fission product cesium isotopes ¹³⁵Cs and ¹³⁷Cs at low femtogram (fg) 10⁻¹⁵ levels in ground water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is reported. To eliminate the natural barium isobaric interference on the cesium isotopes, in-line chromatographic separation of the cesium from barium was performed followed by high sensitivity ICP-MS analysis. A high efficiency desolvating nebulizer system was employed to maximize ICP-MS sensitivity ~10 cps/fg. The three sigma detection limit for ¹³⁵Cs was 2 fg/mL (0.1 μBq/mL) and for ¹³⁷Cs 0.9 fg/mL (0.0027 Bq/mL) measured from the standard with analysis time of less than 30 min/sample. Cesium detection and 135/137 isotope ratio measurement at very low femtogram levels using this method in a spiked ground water matrix is also demonstrated.     

Production and chemical separation of <Superscript>48</Superscript>V

Summary Vanadium-48 was produced with an activity of 222 MBq (6 mCi) by the ^natTi(d,xn)⁴⁸V nuclear reactions in the U-120 cyclotron. The energy of the irradiating beam was 13 MeV, its intensity 5 μA, and the metallic Ti target dimension 11’11 mm² (0.1 mm thickness). For target cooling, circulated water in target backside was used. After 3 cooling days, only ⁴⁸V and some ⁴⁶Sc (T_1/2 = 83.8 d), produced by the side nuclear reaction ⁴⁸Ti(d,α)⁴⁶Sc were found in the target. For production of the radiotracer of ⁴⁸V and for the preparation of source for standardization of ⁴⁸V by 4πβ-γ coincidence, the Ti target was dissolved either in HF or in H₂SO₄. For both dissolving methods an ion-exchange separation procedure was developed.     

Extraction chromatography for the separation of <Superscript>239</Superscript>Np from <Superscript>243</Superscript>Am

Summary An extraction chromatography method was developed for the separation of 239Np from ²⁴³Am in nitric acid solution. A sorbent based on aliphatic quaternary amine Aliquat-336 and hydrophobized silica gel was prepared. ²³⁹Np reduced to the oxidation state(IV) with ferrous sulfamate in 2M or 6M HNO₃ sorbs on the prepared silica gel column. After washing with 0.1M ferrous sulfamate in 2.5M HNO₃, ²³⁹Np is eluted with 0.1M HNO₃ containing 0.02M HF. The separation of ²⁴³Am from ²³⁹Np is very effective. The purity of ²³⁹Np was found to be better than 99.5%. The proposed ²³⁹Np milking procedure is suitable for the preparation of ²³⁹Np tracer that can be used for the determination of ²³⁷Np radiochemical yield.     

Preparation of <Superscript>26</Superscript>Al, <Superscript>59</Superscript>Ni, <Superscript>44</Superscript>Ti, <Superscript>53</Superscript>Mn and <Superscript>60</Superscript>Fe from a proton irradiated copper beam dump

The station for pions cancer therapy was operated at PSI from 1980 to 1992. After a cooling time of 12 years it’s made of copper beam dump was cut and samples were taken for analytical purposes. The sampling collected about 500 g of high active copper chips that can be used for separation of exotic radionuclides. The analyses by gamma spectrometry, LSC and AMS showed main nuclides present to be ⁶⁰Co, ⁵⁴Mn, ²²Na, ⁶⁵Zn, ²⁶Al, ⁵³Mn, ⁵⁹Ni, ⁶³Ni, ⁵⁵Fe and ⁶⁰Fe and ⁴⁴Ti with a daughter nuclide ⁴⁴Sc. In the frame of ERAWAST project a procedure combining selective precipitation and ion exchange for the separation of the rare radionuclides from the copper beam dump was developed. The proposed separation procedure is easy for remote controlled implementation in a hot cell. The ion exchange separation of Ni, Al, Mg, Ti and Fe was complete and high decontamination factors for copper and cobalt were achieved. Based on the developed procedure a remotely controlled system for separation of exotic radionuclides from the copper chips was set up. The full scale system was installed in a hot cell where high activity levels can be handled. In order to evaluate the reliability and functionality of the system extensive tests have been done. During the test period 13.86 g in total of the proton irradiated copper beam dump were processed for separation of ²⁶Al, ⁵⁹Ni, ⁵³Mn, ⁴⁴Ti and ⁶⁰Fe. The results showed that the system was operational and the radionuclide separation was selective with high chemical yield. The procedure manages as well the generated liquid wastes containing high level of ⁶⁰Co activity.     

Systematic radiochemical separation for the determination of <Superscript>99</Superscript>Tc, <Superscript>90</Superscript>Sr, <Superscript>94</Superscript>Nb, <Superscript>55</Superscript>Fe and <Superscript>59,63</Superscript>Ni in low and intermediate radioactive waste samples

A simple and rapid separation procedure was systemized for the determination of ⁹⁹Tc, ⁹⁰Sr, ⁹⁴Nb, ⁵⁵Fe and ^59,63Ni in low and intermediate level radioactive wastes. The integrated procedure involves precipitation, anion exchange and extraction chromatography for the separation and purification of individual radionuclide from sample matrix elements and from other radionuclides. After separating Re (as a surrogate of ⁹⁹Tc) on an anion change resin column, Sr, Nb, Fe and Ni were sequentially separated as follows; Sr was separated as Sr (Ca-oxalate) co-precipitates from Nb, Fe and Ni followed by purification using Sr-Spec extraction chromatographic resin. Nb was separated from Fe and Ni by anion exchange chromatography. Fe was separated from Ni by anion exchange chromatography. Ni was separated as Ni-dimethylglyoxime precipitates after the removal of ^134,137Cs and ^110mAg by Cs-phosphotungstate and AgCl precipitation, respectively. Finally, the radionuclide sources were prepared by precipitation for their radioactivity measurements. The reliability of the procedure was evaluated by measuring the recovery of chemical carriers added to a synthetic radioactive waste solution.     

Sequential separation of <Superscript>99</Superscript>Tc, <Superscript>94</Superscript>Nb, <Superscript>55</Superscript>Fe, <Superscript>90</Superscript>Sr and <Superscript>59/63</Superscript>Ni from radioactive wastes

A sequential separation procedure has been developed for the determination of ⁹⁹Tc, ⁹⁴Nb, ⁵⁵Fe, ⁹⁰Sr and ^59/63Ni in various radioactive wastes generated from nuclear power plants. Ion exchange and extraction chromatography were adopted for individual separation of the radionuclides. Precipitation was supplementarily utilized for both purification of the individual radionuclides and preparation of the radionuclide sources for use in a radioactivity measurement. The chromatographic separation behavior of the radionuclides both from the sample matrix metals and from one another was investigated using stable metals, Re (as a surrogate of ⁹⁹Tc), Nb, Fe, Sr and Ni. The validity of the procedure for reliability and applicability was evaluated by measuring the recovery of the metal carriers added to synthetic radioactive waste solutions. The recoveries by the chromatographic separation were in the range of 84.8 to 102.2% with 2s of less than 8.6%, the recoveries by the precipitation being in the range of 84.3 to 97.3% with 2s of less than 10.9%.     

Disequilibrium of dissolved <Superscript>234</Superscript>U/<Superscript>238</Superscript>U and <Superscript>210</Superscript>Po/<Superscript>210</Superscript>Pb in Greek rivers

For the first time, a radiological study for the dissolved ²³⁸U, ²³⁴U, ²¹⁰Pb and ²¹⁰Po was held in major Greek rivers across the country. ²³⁴U/²³⁸U activity ratios are above one in all samples and ²¹⁰Po/²¹⁰Pb activity ratios are respectively below the unit indicating the disequilibrium in the samples. Quite satisfactory correlations were observed among ²³⁴U and ²³⁸U as well as among ²¹⁰Po and ²¹⁰Pb values. Uranium isotopes were separated by ion exchange and electroplated on stainless steel plates. ²¹⁰Po was spontaneously deposited on nickel plates, while ²¹⁰Pb was indirectly determined through the ingrowth of ²¹⁰Po. The sources were measured by a-spectrometry.     

Production of monoenergetic MeV-range neutrons by <Superscript>3</Superscript>H(p,n)<Superscript>3</Superscript>He reaction

Monochromatic MeV-energy neutron source for secondary reaction was developed utilizing tritium embedded titanium (Ti-³H) thin film via ³H(p,n)³He reaction. We have measured the neutron energies and the energy spread by resonance reactions of ¹²C(n,tot) and ²⁸Si(n,tot). The available energy was within the range from 0.6 to 2.6 MeV. Energy spread was 1.6% at energy of 2.077 MeV. The flux in the beam direction was determined to be 3.76·10⁷ n/s/sr by irradiating ¹⁹⁷Au by about 2 MeV neutrons. This source was shown to be useful for measurements of nuclear data by measuring the total cross sections of neutrons on Fe and comparing these data to the data of ENDF-6.     

Determination of <Superscript>3</Superscript>H, <Superscript>226</Superscript>Ra, <Superscript>222</Superscript>Rn and <Superscript>238</Superscript>U in Austrian ground- and drinking water

Screening measurements for ³H, ²²⁶Ra, ²²²Rn and ²³⁸U in ground water were performed within a ground- and drinking water project in Austria. The aim of this project is to get an overview of the distribution of natural radionuclide activity concentration levels in ground water bodies. In some cases this water is used for drinking water abstraction. In this paper methods and results of the screening measurements are presented. Regions with high activity concentrations were identified and in these regions further investigation for ²²⁸Ra, ²¹⁰Pb and ²¹⁰Po will be conducted.     

<Superscript>234</Superscript>U/<Superscript>238</Superscript>U and <Superscript>235</Superscript>U/<Superscript>238</Superscript>U ratios in domestic water from the environs of Obuasi mine in Ghana

Activity concentrations of ²³⁸U, ²³⁵U and ²³⁴U were determined in different sources of drinking water at the Obuasi gold mines and its surrounding areas in Ghana. Water samples collected from the mines and its surrounding areas were analyzed using direct gamma-ray spectrometry and neutron activation analysis. The ²³⁴U/²³⁸U and ²³⁵U/²³⁸U ratios were calculated and the mean values range from 1.27 to 1.38 and from 0.044 to 0.045 respectively. The average ²³⁴U/²³⁸U ratio was from 1.27 for groundwater to 1.38 for treated water, demonstrating the lack of equilibrium. The average ²³⁵U/²³⁸U activity ratio is 0.045, indicating that only natural uranium was detected in the samples investigated.     

Measurements of <Superscript>210</Superscript>Po and <Superscript>210</Superscript>Pb in total diet samples: Estimate of dietary intakes of <Superscript>210</Superscript>Po and <Superscript>210</Superscript>Pb for Japanese

To estimate the dietary intakes of ²¹⁰Pb and ²¹⁰Po for the Japanese adults and their annual effective doses, ²¹⁰Pb and ²¹⁰Po were measured for 240 daily diet samples collected at two locations of Ishikawa Prefecture in Japan over three years by duplicate portion studies. No appreciable differences in intake rates of ²¹⁰Pb and ²¹⁰Po and their ²¹⁰Po/²¹⁰Pb ratios were seen among the years in each district, and between the two districts. The intake rates evaluated using 240 diet samples were 0.20 Bq/d/p for ²¹⁰Pb and 0.61 Bq/d/p for ²¹⁰Po as a median, respectively. Annual effective doses of ²¹⁰Pb and ²¹⁰Po for Japanese adults were estimated to be 0.050 and 0.053 mSv/y, respectively.     

Analysing of <Superscript>228</Superscript>Th, <Superscript>232</Superscript>Th, <Superscript>228</Superscript>Ra in human bone tissues for the purpose of determining the post mortal interval

The adsorption of Cs on clayey materials such as bentonite and Na-montmorillonite was studied in various electrolytic conditions (concentration and composition), various solid to liquid ratios and various pH conditions. The results obtained for these different conditions were modeled considering an exchange model associated to the surface complexation concept. Then, the same approach was considered to model the sorption of Rb, which have the same chemical behavior than Cs. Experiments were carried out for various electrolyte, pH, and Rb concentrations. The stoichiometries corresponding to the sorption of Rb on bentonite and montmorillonite were then deduced from the experimental results.     

Free Ca<Superscript>2+</Superscript> as an early intracellular biomarker of exposure of cyanobacteria to environmental pollution

Calcium functions as a versatile messenger in a wide variety of eukaryotic and prokaryotic cells. Cyanobacteria are photoautotrophs which have a great ecological impact as primary producers. Our research group has presented solid evidence of a role of calcium in the perception of environmental changes by cyanobacteria and their acclimation to these changes. We constructed a recombinant strain of the freshwater cyanobacterium Anabaena sp. PCC 7120 that constitutively expresses the calcium-binding photoprotein apoaequorin, enabling in-vivo monitoring of any fluctuation in the intracellular free calcium concentration of the cyanobacterium in response to any environmental stimulus. The “Ca²⁺ signature” is the combination of changes in all Ca²⁺ signal properties (magnitude, duration, frequency, source of the signal) produced by a specific stimulus. We recorded and analyzed the Ca²⁺ signatures generated by exposure of the cyanobacterium to different groups of environmental pollutants, for example cations, anions, organic solvents, naphthalene, and pharmaceuticals. We found that, in general, each group of tested chemicals triggered a specific calcium signature in a reproducible and dose-dependent manner. We hypothesize that these Ca²⁺ signals may be related to the cellular mechanisms of pollutant perception and ultimately to their toxic mode of action. We recorded Ca²⁺ signals triggered by binary mixtures of pollutants and a signal induced by a real wastewater sample which could be mimicked by mixing its main constituents. Because Ca²⁺ signatures were induced before toxicity was evident, we propose that intracellular free Ca²⁺ may serve as an early biomarker of exposure to environmental pollution.