Determination of <Superscript>241</Superscript>Am/<Superscript>243</Superscript>Am ratios

Determination of ²⁴¹Am/²⁴³Am ratios is required for vanous purposes including assay of Am by isotope dilution techniques. Alpha-spectrometry on electrodeposited sources is a preferred technique for this determination. However, there is an inherent problem of tail contribution which necessitates the use of suitable algorithms to account for the same. Recently, in the frame of a Coordinated Research Program (CRP) of the International Atomic Energy Agency (IAEA), WinALPHA software has been developed which is a combination of an asymmetrical Gaussian for the main part of the peak and a low energy function. Therefore, it was of interest to compare the use of this algorithm with the routinely used method, in our laboratory, based on geometric progression (G. P.) decrease. Since, there are no reference materials available commercially for ²⁴¹Am/²⁴³Am ratios, synthetic mixtures covening a wide range (0.3 to 2.0) of ²⁴¹Am/²⁴³Am α-activity ratios were used and un-ignited electrodeposited sources were prepared for α-spectrometry. The α-spectra obtained using PIPS detector, were evaluated using the two algonthms The ²⁴¹Am/²⁴³Am α-activity ratios obtained were also compared with those determined by thermal ionization mass spectrometry (TIMS). An agreement of about 1% was obtained in the ²⁴¹Am/²⁴³Am ratios determined by the two methods and also by using the two algorithms for α-spectrum evaluation.     

Separation and determination of <Superscript>241</Superscript>Am in urine samples from radiation workers using PC88-A and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of ²⁴¹Am isotope in urine samples using Extraction Chromatography (EC) and ²⁴³Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.     

Biosorption of <Superscript>241</Superscript>Am by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>: Preliminary investigation on mechanism

As an important radioisotope in nuclear industry and other fields, ²⁴¹Am is one of the most serious contamination concerns due to its high radiation toxicity and long half-life. The encouraging biosorption of ²⁴¹Am from aqueous solutions by free or immobilized Saccharomyces cerevisiae (S. cerevisiae) has been observed in our previous experiments. In this study, the preliminary evaluation on mechanism was further explored via chemical or biological modification of S. cerevisiae, and using europium as a substitute for americium. The results indicated that the culture times of more than 16 hours for S. cerevisiae was suitable and the efficient adsorption of ²⁴¹Am by the S. cerevisiae was able to achieve. The pH value in solutions decreased gradually with the uptake of ²⁴¹Am in the S. cerevisiae, implying that H⁺ released from S. cerevisiae via ion-exchange. The biosorption of ²⁴¹Am by the decomposed cell wall, protoplasm or cell membrane of S. cerevisiae was same efficient as by the intact fungus. However, the adsorption ratio for ²⁴¹Am by the deproteinized or deacylated S. cerevisiae dropped obviously, implying that protein or carboxyl functional groups of S. cerevisiaece play an important role in the biosorption of ²⁴¹Am. Most of the investigated acidic ions have no significant influence on the ²⁴¹Am adsorption, while the saturated EDTA can strong inhibit the biosorption of ²⁴¹Am on S. cerevisiae. When the concentrations of coexistent Eu³⁺, Nd³⁺ were 100 times more than that of ²⁴¹Am, the adsorption ratios would decrease to 65% from more than 95%. It could be noted by transmission electron microscope (TEM) analysis that the adsorbed Eu is almost scattered in the whole fungus, while Rutherford backscattering spectrometry (RBS) analysis indicated that Ca in S. cerevisiae have been replaced by Eu via ion-exchange. All the results implied that the adsorption mechanism of ²⁴¹Am on S. cerevisiae is very complicated and at least involved in ion exchange, complexation process as well as well as nonspecific adsorption in cell wall because of static electricity.     

Modified <Emphasis Type="Italic">Rhizopus arrhizus</Emphasis> biomass for sorption of <Superscript>241</Superscript>Am and other radionuclides

The improvement and the refinement of non-viable Rhizopus arrhizus biomass were investigated via immobilization. Immobilization was carried out by using sodium alginate/CaCl₂ solution and formaldehyde/HCl cross-linking with dead Rhizopus arrhizus biomass and were used for the sorption of radionuclides from low level effluent wastes. The sodium alginate/CaCl₂ immobilized biomass (ratio 1:2) showed about 86% sorption for ²⁴¹Am activity but due to its soft nature and tendency to undergo distortion in shape, is unsuitable for practical applications. The biomass cross-linked with 15% formaldehyde/0.1 M HCl solution has a relatively high mechanical strength and rigidity. It was showing a sorption of >99% for ²⁴¹Am activity and has the sorption capacity of ~65 mg/g for americium and uranium. Hence, it can be utilized for the removal of radionuclides from radioactive waste effluents.     

Adsorption and migration of <Superscript>241</Superscript>Am in aerated zone soil

As an important radioisotope in nuclear industry and other fields, ²⁴¹ Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful reference for disposal of ²⁴¹Am waste with low-medium radioactivity, the adsorption and migration behavior of ²⁴¹Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that more than 98% of the total ²⁴¹Am could be adsorbed from ²⁴¹Am solution of 0.32·10⁻⁷−1.1·10⁻⁷ mol/l by the soil at pH 4–9. The adsorption of ²⁴¹Am on the soil was a pH-dependent process at pH<4, but for pH>4, the adsorption rate of ²⁴¹Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption of ²⁴¹Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of ²⁴¹Am and adsorption capacities of ²⁴¹Am can be described by the Freundlich adsorption equation. Adsorption of ²⁴¹Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated EDTA solution, C₂O₄ ²⁻ and CO₃ ²⁻. It was also noted that the adsorption rate of ²⁴¹Am drops in solutions containing Eu³⁺ or Nd³⁺, even 0.5 times above the ²⁴¹Am concentration. A migration distance of 8 mm for ²⁴¹Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient sorbent for ²⁴¹Am and can inhibit the migration of ²⁴¹Am.     

Purification and separation of <Superscript>239+240</Superscript>Pu and <Superscript>241</Superscript>Am in biological samples by anion-exchange and extraction chromatography for high resolution alpha-spectrometry analyses

Many biological samples (urines and faeces) have been analyzed by means of chromatographic extraction columns, utilizing two different resins (AG 1-X2 resin chloride and TRU), in order to detect the possible internal contamination of ^239+240Pu and ²⁴¹Am for some workers of a reprocessing nuclear plant in the decommissioning phase. The results obtained show on one hand the great suitability of the first resin for the determination of plutonium, and on the other, the great selectivity of the second one for the determination of americium.     

Behavior and distribution of <Superscript>239+240</Superscript>Pu and <Superscript>241</Superscript>Am in the east coast of Peninsular Malaysia marine environment

The present distributions of ^239+240Pu, ²⁴¹Am and activity ratio of ²⁴¹Am/^239+240Pu in surface seawater of the Peninsular Malaysia east coast were studied. The surface seawater samples were collected at 30 identified stations during the expedition conducted in 2008. ^239+240Pu activity concentrations in surface seawater of the studied area were in the range of 2.33 ± 0.20–7.95 ± 0.68 mBq/m³, meanwhile ²⁴¹Am activity concentrations ranged from MDA to 1.90 ± 0.23 mBq/m³. The calculated activity ratios of ²⁴¹Am/^239+240Pu were varied and disperse distributed with the ranged of 0.12–0.53. The relationships between anthropogenic radionuclide and oceanographic parameters such as turbidity and salinity were examined. The linearly relationships between ^239+240Pu and oceanographic parameters are important for better understanding of its transport processes and behavior in the east coast of Peninsular Malaysia marine environment. Thus, the differ of distribution of ^239+240Pu, ²⁴¹Am and ²⁴¹Am/^239+240Pu in the studied area mainly due to high affinity of ^239+240Pu to associate with sinking particles, mobility nature of ²⁴¹Am, degree of particle reactive of both anthropogenic radionuclides, scavenging and removal process; and others.     

Study of the <Superscript>241</Superscript>Am(n,2n)<Superscript>240</Superscript>Am reaction cross section in the energy range of <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> = 8.8−11.1 MeV

The measurement of the cross section of the reaction ²⁴¹Am(n,2n)²⁴⁰Am has been performed at neutron energies from 8.8 to 11.1 MeV, implementing the activation technique. The neutron beam was produced at the TANDEM accelerator of NCSR “Demokritos” by the ²H(d,n)³He reaction, using a deuterium gas target. During the 5-day long irradiation, the neutron beam fluctuations were monitored in 100 seconds intervals by a BF₃ counter connected with a multiscaling unit. The radioactive target consisted of a 37 GBq ²⁴¹Am source enclosed in a Pb container. A natural Au foil, a ²⁷Al foil and a ⁹³Nb foil were used as reference materials for the neutron flux determination. After the end of the irradiation the activity induced at the target and the reference foils, was measured off-line by a 56% HPGe detector.     

Attempt to reduce <Superscript>239</Superscript>Pu and <Superscript>241</Superscript>Am uptake by wheat plantlets by application of inorganic fertilizers

Inorganic fertilizers are applied to reduce plant uptake of anthropogenic radionuclides, but scarce data are available for ²³⁹Pu and ²⁴¹Am. Wheat plantlets were grown in laboratory on limited amount of soil with ²³⁹Pu, ²⁴¹Am and different application rates of NPK and diammonium phosphate (DAP). As rates increased, the uptake of ²³⁹Pu and ²⁴¹Am to the whole plantlet also increased. It was higher for DAP than for NPK, (higher supply of P₂O₅ and NH₄ ⁺). Root content was higher than shoots for all experiences, suggesting low mobility within the plantlet. Root content increased with fertilizer rate, but practically no effect in shoots.     

Determination of <Superscript>241</Superscript>Am in urine using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS)

Quantification of ²⁴¹Am in urine at low levels is important for assessment of individuals’ or populations’ accidental, environmental, or terrorism-related internal contamination, but no convenient, precise method has been established to rapidly determine these low levels. Here we report a new analytical method to measure ²⁴¹Am as developed and validated at the Centers for Disease Control and Prevention (CDC) by means of the selective retention of Am from urine directly on DGA resin, followed by SF-ICP-MS detection. The method provides rapid results with a limit of detection (LOD) of 0.22 pg/L (0.028 Bq/L), which is lower than 1/3 of the C/P CDG for ²⁴¹Am at 5 days post-exposure. The results obtained by this method closely agree with CDC values as measured by liquid scintillation counting, and with National Institute of Standards Technology (NIST) Certified Reference Materials (CRM) target values.     

<Superscript>241</Superscript>Pu in the environment: insight into the understudied isotope of plutonium

Studies of plutonium in the environment have focused on the α-emitting isotopes ²³⁸Pu, ²³⁹Pu and ²⁴⁰Pu, often overlooking the β-emitting isotope ²⁴¹Pu  because of its relatively short half-life (14.4 years). Here, we summarize sources of  ²⁴¹Pu and discuss its distribution and behavior in the environment. In the short term, ²⁴¹Pu, the largest contributor to the total plutonium radioactivity whereas in the long term its decay products, ²⁴¹Am and ²³⁷Np, are the major contributors as some 46% of current total ²⁴¹Am is attributable to ²⁴¹Pu decay. In this context, understanding the fate and transport of ²⁴¹Pu is crucial to assessing long-term radiological dose.     

Determination of plutonium and <Superscript>90</Superscript>Sr in air particulate samples

Within the surveillance program of the gaseous effluents coming from the nuclear reprocessing plant EUREX of ENEA (Italian National Agency for New Technologies Energy and Environment, CR Saluggia) in the North of Italy, the content of some radionuclides is continuously monitored. The so-called 1AW high-activity liquid waste (HLLW) is the aqueous raffinate of the first cycle of PUREX extraction process which was the starting point of the reprocessing activity of some MTR and CANDU spent fuel elements. Nowadays, 1AW-HLLW is stored in five tanks placed inside the EUREX plant site. This paper describes the sampling and radioanalytical methods employed to determine the activities of ²⁴¹Am, plutonium isotopes and ⁹⁰Sr in the total suspended particulate material (TSP) of the 1AW tank primary ventilation air circuit.     

Separation and purification of <Superscript>249</Superscript>Cf and <Superscript>245</Superscript>Cm

There is a need to provide radioactivity standards of the higher actinides in support of both decommissioning and remediation activities as well as routine environmental analysis. In the case ²⁴⁹Cf, this will provide a useful calibration nuclide for both α-and γ-spectrometry as well as improving knowledge of the decay scheme for this nuclide. There is anecdotal evidence to suggest that the chemical yield of americium and curium may differ in radiochemical analysis. Thus, a chemical yield tracer of ²⁴⁵Cm may help to resolve this issue and will be suitable for both, suitable for use as a chemical yield tracer for both α-particle spectrometry and mass spectrometry. An aged source of ²⁴⁹Cf was used as the source material for the separation of these two nuclides by cation-exchange, using 2-hydroxy-2-methyl-propanoic acid at controlled pH as an eluant, ²⁴⁹Cf being eluted before the ²⁴⁵Cm daughter. The purity of both nuclides was measured by γ-ray spectrometry.     

Dosage de l'americium par coulometrie a potentiel impose

A coulometric determination of americium by reduction of Am(VI) to Am(V) at a potential of + 1.3 V is proposed. The accuracy of the method was evaluated by analyzing ²⁴¹Am solutions prepared by weighing and dissolving AmO₂ of known purity. The results must be corrected by a factor of 1.017, in order to eliminate the systematic error due to autoreduction. After this correction, the relative standard deviation of the method ranged from 0.44% for américium concentrations of 3.125·l0^-3M to 0.96% for those of 1.25·10^-4M.     

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.     

Sorption behavior of Am<Superscript>3+</Superscript> on suspended pyrite

Sorption behavior of ²⁴¹Am (~10⁻⁹ M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO₄)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10⁻⁴ M CO₃ ²⁻, SO₄ ²⁻, C₂O₄ ²⁻ and PO₄ ³⁻), di- and trivalent metal ions (1 × 10⁻³ M Mg²⁺, Ca²⁺ and Nd³⁺) on sorption behavior of Am³⁺ at a fixed ionic strength (I = 0.10 M (NaClO₄)) have been studied. The sorption of ²⁴¹Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of ²⁴¹Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of ²⁴¹Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C₂O₄ ²⁻ (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on ²⁴¹Am sorption. The presence of Mg²⁺, Ca²⁺ ions showed marginal effect on the sorption profile of ²⁴¹Am; while the presence of Nd³⁺ ion suppressed its sorption significantly under the conditions of present study. The sorption of ²⁴¹Am on pyrite decreased with increased temperature indicating an exothermic process.     

Purification of americium from assorted analytical waste in hydrochloric acid medium

During the simultaneous extraction of plutonium and uranium using anion exchange chromatographic technique from analytical waste in hydrochloric acid medium, ²⁴¹Am which is invariably present in the plutonium bearing fuel samples remains in the effluent. A two step separation scheme was developed for the recovery and purification of Am from the assorted waste to facilitate the disposal of large volume of aqueous waste and the purified Am solution was utilized for spectroscopic investigation. The separation scheme involved solvent extraction using 0.1 M TODGA + 0.5 M DHOA for separation of americium from Fe, Pb, Ni and Na followed by extraction chromatographic technique using CMPO on inert support as stationary phase for separation of Ca from Am. A systematic study on the extraction behavior of Am from hydrochloric acid medium revealed that out of four extraction systems well known for actinide partitioning namely 0.1 M TODGA + 0.5 M DHOA, 1 M DMDBTDMA, 0.2 M CMPO + 1.2 M TBP and 30% TRPO, only 0.1 M TODGA + 0.5 M DHOA extracts americium from 7.5 M HCl feed acidity. A comparative study involving CMPO solvent extraction and column chromatographic technique revealed that elution of Am from column is satisfactory as compared to inefficient stripping of Am from organic phase in solvent extraction technique using 0.1 M HNO₃. The purity of the final solution was checked for 17 elements of interest and was found to be 98% pure, while the overall recovery of this two step separation scheme was found to be 95%.     

Determination of rare earth elements at trace levels in uranium process stream samples by ion-interaction chromatography

To accurately determine ²⁴¹Am by mass spectrometry, interfering elements (IEs) including Bi, Hf, Hg, Pb, Pt, Pu and Tl need to be decontaminated. In this study, the extraction behaviors of IEs in HNO₃ and HCl mediums were systematically studied for the employed extraction resins (TRU, DGA-N and DGA-B). Based on the results, chemical separation procedures were proposed. After cooperation with proper co-precipitation methods, the proposed procedures can be used to determine ²⁴¹Am in environmental samples. The results of evaluation showed that IEs in soil samples were completely removed and ²⁴¹Am was accurately determined for all proposed procedures.