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.     

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.     

Determination of activity ratios of <Superscript>238,239+240,241</Superscript>Pu, <Superscript>241</Superscript>Am, <Superscript>134,137</Superscript>Cs,and <Superscript>90</Superscript>Sr in Bulgarian soils

The origins of different artificial radionuclides found in soils from Northern and Southern Bulgaria was determined by measurements of their actual concentrations and respective ratios. On the basis of the measured mobility and concentrations of the investigated radionuclides in soils, it was estimated that after the Chernobyl accident the mean depositions of fresh ¹³⁷Cs were 3.0 ± 2.5 kBq/m² for Northern Bulgaria and 15 ± 7 kBq/m² for Southern Bulgaria. As a result of global fallout following atmospheric nuclear weapon tests in the 1950s, mean depositions (corrected to 1965) were calculated for Northern and Southern Bulgaria as follows: for ⁹⁰Sr—1.0 ± 0.5 and 2.3 ± 1.3 kBq/m², ²³⁸Pu—1.3 ± 0.8 and 2.8 ± 1.6 Bq/m², ^239+240Pu—15 ± 14 and 47 ± 38 Bq/m², and ²⁴¹Pu—520 ± 200 and 760 ± 260 Bq/m².     

<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 <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.     

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.     

Characterization of purified <Superscript>241</Superscript>Am for common impurities by instrumental neutron activation analysis

Americium is an important actinide element having versatile applications based on its alpha and gamma emissions. Multi-element determination of radioactive samples using ICP-AES technique may be affected by the presence of americium due to its rich emission spectra. With a view to characterize plutonium based fuels containing americium for trace metals by ICP-AES technique accurately, a high purity ²⁴¹Am (using a separation procedure developed in our laboratory) was prepared. To ascertain its chemical purity it is essential to determine its impurity contents accurately. Instrumental neutron activation analysis (INAA), being a sensitive multi-elemental technique, was employed to determine the concentrations of impurities in purified ²⁴¹Am. Detection limits for the common elements and rare earth elements have also been determined. Comparison is made with the analytical data obtained by the ICP-AES method.     

An ion chromatographic separation method for the sequential determination of <Superscript>90</Superscript>Sr, <Superscript>241</Superscript>Am and Pu isotopes in a urine sample

A radiobioassay method has been developed for the sequential determination of ⁹⁰Sr, ²⁴¹Am and Pu isotopes in a urine sample. Unlike the existing methods using multiple extraction chromatographic cartridges, this work demonstrates an application of an automated ion chromatographic (IC) system for the separation of these radionuclides on a single IC column. The method meets the bioassay performance criteria for relative bias and relative precision as recommended by ANSI/HPS N13.30-2011. The detection limits for the radionuclides are found to be satisfactory for medical intervention in case of an accidental exposure scenario. Sample preparation time is less than 11 h.     

Sensitivities and detection limits of X-ray fluorescence analysis with a 10 mCi<Superscript>241</Superscript>Am source

A method is discussed, which is preferentially used for rapid analyses. After fusion of the sample with dipotassium disulphate and dissolution of the molten mass in water, antimony is titrated with potassium bromate in hydrochloric solution without separating the matrix. 5–7% of Sb can be determined with a standard deviation of 0.04%.     

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.     

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.     

Distribution of uranium,plutonium, and <Superscript>241</Superscript>Am in soil samples from Idaho National Laboratory

Soil materials used were collected in the early 1970s at Idaho National Laboratory near the Subsurface Disposal Area (SDA). Samples from a depth of 0–4 and 4–8 cm at two different sites located on the northeast corner of the SDA perimeter were analyzed. The concentration of ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U in soil digests were measured by mass spectrometry. Uranium isotopic composition of the soil at the two sample sites and depths is compared to previously measured concentrations of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, and ²⁴¹Am. Implications for remediation of contaminated soils surrounding the SDA are discussed.     

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.     

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.     

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.     

Flux calculation in LSNAA using an <Superscript>241</Superscript>Am-Be source

The CITATION code based on neutron diffusion theory is used for flux calculation inside voluminous sample in prompt gamma activation analysis with an isotopic neutron source (²⁴¹Am-Be). The code used the specific parameters related to energy spectrum source, irradiation system materials (shielding, reflector, etc.), geometry and elemental composition of the sample. The flux distribution (thermal and fast) was calculated on three-dimensional geometry for the system: source, air, and polyethylene and water cylindrical sample of 125 liters. The thermal flux was calculated in series of points inside the sample, and agreed with the results obtained by measurements with good statistical uncertainty. The maximum thermal flux was measured at distance of 4.1 cm and calculated at 4.3 cm by the CITATION code. Beyond a depth of 7.2 cm, the ratio of thermal flux to fast flux increases up to twice and allows us the optimization of the detection system in the scope of in-situ PGNAA.     

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.     

Determining the activity of <Superscript>241</Superscript>Pu by liquid scintillation counting

Liquid scintillation counting (LSC) is one of the most widely used methods for determining the activity of ²⁴¹Pu. One of the main challenges of this counting method is the efficiency calibration of the system for the low beta energies of ²⁴¹Pu (E _max = 20.8 keV). In this paper we compare the two most frequently used methods, the CIEMAT/NIST efficiency tracing (CNET) method and the experimental quench correction curve method. Both methods proved to be reliable, and agree within their uncertainties, for the expected quenching conditions of the sources.     

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.