Gamma-spectrum of241Am

The γ-ray spectrum of²⁴¹Am was reinvestigated by using intense sources. A purified solution source was used to make sure that the γ-lines presents in the spectrum come from the α-decay of²⁴¹Am. The γ-spectrometer consists of 40% relative efficiency HPGe detector and 8192-channel ADC. Out of 137 γ-lines that are presents in the spectrum 46 are new.     

The Formation of Analytical and Background Signals in Radioisotope X-ray Fluorescence Analysis Using a 241Am Radioactive Source and a Si(Li) Detector

Reasons for the appearance of a background signal in the relatively soft x-ray range (2–15 keV) upon fluorescence excitation with the ²⁴¹Am radioisotope are discussed. Mathematical models are proposed for the interaction of the radiation of the radioactive source with the sample and the Si(Li) detector, capable of describing the appearance of the analytical and background signals. It was shown that processes occurring in the Si(Li) detector should be taken into account to explain and calculate the background signal in this range. The results of calculations agree well with the experimental data obtained using an ²⁴¹Am radiation source for fluorescence excitation.     

Comparison of alpha-spectrometry and alpha/gamma ratio method for the determination of americium in plutonium bearing fuel materials

Determination of americium is one of the requirements of chemical quality assurance of plutonium bearing fuel materials. Alpha-spectrometry is generally used for the determination of ²⁴¹Am in Pu bearing fuels since the efficiency of semiconductor detector used for alpha-spectrometry is independent of the alpha-particle energy in the 4 to 8 MeV range. However, this method has limitations for Pu samples containing extremely small or very large amounts of ²⁴¹Am. Thus an alternative methodology based on alpha/gamma (α/γ) activity ratio was developed and tested using different samples. The method is based on the determination of total γ-activity (of 60 keV peak) of an aliquot of the solution and the total α-activity present in the aliquot. The method is fast as it does not involve chemical separation of Pu and Am as required in the alpha-spectrometric method. Data obtained on synthetic and real life samples demonstrates the usefulness of the developed alpha/gamma ratio method for the determination of ²⁴¹Am in Pu bearing fuel samples.     

Assessments on energy and efficiency calibration of an alpha spectrometry system using standard sources

Studies and evaluations of the main parameters of a high resolution multi-chamber alpha spectrometer and its full calibration using standard sources of ²⁴¹Am, ²³³U and ²⁴⁴Cm are presented for the validation of the complex method of characterization of an alpha spectrometer dedicated for alpha radioactive concentration measurements of various environmental samples. The resolution and efficiency were determined at all possible source-detector distances for all eight solid state ORTEC ULTRA-AS detectors. In addition, the solid angles associated to different measurement geometries and the repeatability of the results were assessed. A detailed inter-comparison of the results was performed drawing important conclusions regarding the quality of the alpha detector response to the alpha radiation of the standard sources used in measurements.     

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.     

A gamma monitoring technique for estimating plutonium contamination around nuclear weapons facilities

The objectives of this study were to establish a ratio for²⁴¹Am to²³⁹Pu in soil at the Rocky Flats Plant and to compare²⁴¹Am concentrations obtained using in-situ and laboratory gamma spectroscopy measurements to concentrations determined with radiochemical analysis and alpha spectroscopy. Soil samples were collected for radiochemical and laboratory gamma spectroscopy analysis from vertical profiles in 3 cm layers to a depth of 21 cm at predetermined locations along transects oriented in the direction of prevailing winds. The origin for the transects was the center of the 903 Pad at the Rocky Flats Plant, which is believed to be the source for most of the²⁴¹Am and²³⁹Pu contamination. A 100 minute in-situ gamma spectroscopy measurement was made at each soil sample location with a portable HPGe detector. Soil samples were dried, passed through a 2 mm sieve, mixed, and split in two fractions. One fraction was analyzed radiochemically for²⁴¹Am and²³⁹Pu and the second was analyzed using laboratory gamma spectroscopy. The median ratio of²⁴¹Am to²³⁹Pu activities, which appears to be independent of soil depth and distance from suspected sources, was 0.17. There is a strong correlation between²⁴¹Am and²³⁹Pu concentrations determined using radiochemical analysis with alpha spectroscopy and concentrations determined with laboratory gamma spectroscopy. Results from in-situ gamma spectroscopy measurements were also correlated with the radiochemical analyses but exhibited greater variability than laboratory measurements. This on-going investigation has demonstrated that it is possible to indirectly measure²³⁹Pu concentrations in soil if the ratio of²⁴¹Am to²³⁹Pu can be established. The results indicate that judicious use of a combination of radiochemical analyses with laboratory and in-situ gamma spectroscopy measurements may provide a cost-effective approach for characterization of large sites where²⁴¹Am and²³⁹Pu contamination occur.     

Low level Pu and Am estimation in liquid waste from nuclear reactor

Estimation of very low amount up to pico-gram of Am and Pu in the liquid waste of U–Pu fuel cycle of the irradiated U fuel from the nuclear reactor has been carried out using combined method of α- and γ-ray spectrometric techniques. ²⁴¹Am was estimated by γ-ray spectrometry from a plancheted source. In spite of the same α energy of 5.49 MeV for ²⁴¹Am and ²³⁸Pu, the amount ²³⁸Pu was estimated by α spectrometry from the same plancheted source after subtracting amount of the ²⁴¹Am obtained from γ-ray spectrometry. The amount of Am and Pu obtained by this technique is found to be superior compared to other techniques even in the presence of Th, U and fission products.     

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.     

Simultaneous determination of 152Eu and 241Am in liquid solution by liquid scintillation counting

¹⁵²Eu and ²⁴¹Am are the most frequently used radiotracers in the separation studies on trivalent minor actinides and lanthanides. In almost all those studies, the determination of ¹⁵²Eu and ²⁴¹Am has been based on measuring their γ radiation by using a NaI(Tl) scintillation detector and/or a germanium detector. In this study, based on measuring the β particles and mono-energy electrons from ¹⁵²Eu and the α particles from ²⁴¹Am, we provide a new option to simultaneously determine the radioactivities of ¹⁵²Eu and ²⁴¹Am by liquid scintillation counting (LSC) with the aid of α/β discrimination. If the count rate ratio of ²⁴¹Am to ¹⁵²Eu is within the range of 100:1–1:100, the radioactivities of ¹⁵²Eu and ²⁴¹Am in mixed samples can be simultaneously determined by LSC with the errors less than 5 %. In addition, the interferences of ²⁴¹Am on Eu are divided into two parts: inside and outside the ²⁴¹Am region of interest. Only if the count rate ratio of ²⁴¹Am to Eu is more than 10:1, should the latter interference be in consideration.     

Studies on the age determination of trace plutonium

An isotope dilution multicollector inductive coupled plasma mass spectrometry (ID-MC-ICP-MS) method for determining age of trace Pu through measuring ²⁴¹Pu/²⁴¹Am, ²⁴⁰Pu/²³⁶U ratio was established. At the same time, other two methods-α-spectrometry combined with MC-ICP-MS and liquid scintillator combined with α-spectrometry through measuring ²⁴¹Pu/²⁴¹Am ratio to determine the age of trace Pu were also studied. The techniques were explored for the age determination of nanogram grade Pu sample on the basis of Pu/Am, Pu/U separation. The ages of two Pu samples—one with known and the other with unknown age—were determined by the three methods. The determined ages by the three methods were all in agreement with the reference value. The established methods for determining the age of trace Pu could be adopted in the verification activities of nuclear safeguards and nuclear arms control.     

Standardization of calibration procedures for quantification of gross alpha and gross beta activities using liquid scintillation counter

Simultaneous measurement of gross alpha and gross beta activities by liquid scintillation counting technique using LKB Wallac Quantulus 1220 liquid scintillation counter (LSC) equipped with Pulse Shape Analyzer (PSA) is described. Three sets of pure alpha and pure beta standards simulating the activity concentration values of real samples in terms of α/β activity ratios were used to calibrate the LSC. Calibration methodology for the Quantulus 1220 with respect to the above measurements using ²⁴¹Am and ⁹⁰Sr/⁹⁰Y standards of respective activity concentrations of ~25 dpm and ~10⁴ dpm is described in detail. Also highlighted the need to calibrate the LSC using another set of ²⁴¹Am and ⁹⁰Sr/⁹⁰Y standards of low and high activity concentrations respectively. The practicability and working performance of these calibration plots was checked by the validation trials with test samples spiked with ²⁴¹Am and ⁹⁰Sr/⁹⁰Y covering range of α/β activity ratios from 1:1 to 1:50.     

The determination of Br,Ag and I in pharmaceuticals using X-ray fluorescence excited by gamma sources

The possibility of using γ-radiation sources for the X-ray fluorescence analysis of Br, Ag, and I was studied on model samples. The results were applied for the determination of these elements in pharmaceutical products. The optimum channel range was selected and the accuracies obtainable with various types of radiation sources were compared. For routine analysis of pharmaceutical products and other substances of similar composition, the most suitable radiation sources are:¹²⁵I for the determination of low concentration of bromine;¹⁵³Gd for the determination of silver; and²⁴¹Am for that of iodine.     

Isotopic composition of plutonium immissions in Austria after the Chernobyl accident

Alpha-spectrometric Pu determinations in aerosol samples collected after the Chernobyl accident in Austria show a²³⁸Pu/²³⁹ (240)Pu ratio in the range of 0.33–0.76 with a most reliable value of 0.47. From²⁴¹Am measurements in old Pu preparations and air filter analyses also²⁴¹Pu activities have been calculated. The ratio²⁴¹Pu/^{239 (240)}Pu during the main contamination period is 74.6±5.7, when maximum²⁴¹Pu concentrations in air achieved 4.5–6.0 mBq/m³.     

Recovery of americium from analytical solid waste containing large amounts of uranium,plutonium and silver

Trace metallic impurity analysis by spectroscopic techniques is one of the important steps of chemical quality control of nuclear fuel materials. Depending on the burn-up and the storage time of the fuel, there is an accumulation of ²⁴¹Am in plutonium based fuel materials due to β decay of ²⁴¹Pu. In this paper, attempts were made to develop a method for separation of ²⁴¹Am from 1.2 kg of analytical solid waste containing 70% U, 23% Pu, 5% Ag and 1–2% C as major constituents along with other minor constituents generated during trace metal assay of plutonium based fuel samples by d. c. arc carrier distillation atomic emission spectrometry. A combination of ion exchange, solvent extraction and precipitation methods were carried out to separate ~45 mg of ²⁴¹Am as Am(NO₃)₃ from 15 L of the analytical waste solution. Dowex 1×4 ion exchange chromatographic method was used for separation of Pu whereas 30% TBP–kerosene was utilized for separation of U. Am was separated from other impurities by fluoride precipitation followed by conversion to nitrate. The recovery of Pu from ion exchange chromatographic separation step was ~93% while the cumulative recovery of Am after separation process was found to be ~90%.     

Precision and accuracy in the determination of plutionium-239 /uranium-233, americium-241/ uranium-233 and curium-244 /uranium-233 alpha activity ratios by alpha spectrometry

Determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios is required when using²³³U as a tracer for the determination of plutonium, americium and curium by alpha spectrometry. Precision and accuracy in the determination of these alpha activity ratios was evaluated by preparing synthetic mixtures from solutions of enriched isotopes of²³⁹Pu,²⁴¹Am,²⁴⁴Cm and²³³U. Separate synthetic mixtures were prepared for each of the three alpha activity ratios. The sources from the synthetic mixtures were prepared by direct evaporation method using tetra ethylene glycol /TEG/ as a spreading agent, alpha spectra were recorded by employing solid state silicon surface barrier detectors coupled to a 4 K analyzer and the alpha spectra were evaluated by a method based on the geometric progression decrease for the far tail of the spectrum. Large area detector /i.e. 450 mm²/ was observed to reduce the effect of nonhomogeneous distribution, if any, of the two elements present in the source. Precision and accuracy of about 1% is demonstrated for the determination of²³⁹Pu/²³³U,²⁴¹Am/²³³U and²⁴⁴Cm/²³³U alpha activity ratios using large area silicon surface barrier detector.     

Alpha spectrum evaluation method for the simultaneous determination of plutonium,americium and curium

A method based on the geometric progression decrease of the counts in the far tail of the alpha spectrum is described for the simultaneous determination of plutonium, americium and curium by alpha spectrometry. For evaluating the precision and accuracy, synthetic mixtures were prepared from solutions of enriched isotopes and sources were prepared by direct evaporation method using tetraethylene glycol /TEG/ as a spreading agent and electropolished stainless steel discs as the backing material. Precision and accuracy of about 1% is demonstrated in the determination of²⁴⁴Cm/²³⁹Pu,²⁴¹Am/²³⁹Pu,²⁴⁴Cm/²³³U,²⁴¹Am/²³³U and²³⁹Pu/²³³U alpha activity ratios using a 450 mm² silicon surface barrier detector.     

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.     

Radiochemical determination of the yields of transuranium nuclides produced from natural uranium irradiated in a reactor

Transuranium nuclides were produced by irradiating a pellet of natural uranium sulfide in the Japan Material Testing Reactor (JMTR). After irradiation, a successive separation of uranium, plutonium, americium and curium was carried out. The fractional concentrations of the nuclides²³⁸Pu,²³⁹Pu,²⁴⁰Pu,²⁴¹Am,²⁴³Am,²⁴²Cm and²⁴⁴Cm were determined by α-ray spectrometry, and those of²⁴¹Pu and^242mAm were estimated from the build-up of α-emitting daughters,²⁴¹Am and²⁴²Cm, respectively. As the yield of²⁴²Pu was too slight to be detected by α-counting, the neutron activation analysis of the plutonium fraction based on the²⁴²Pu(n, γ)²⁴³Pu reaction was carried out by γ-ray spectrometry, and it was shown that a few pg of²⁴²Pu could be determined. A burn-up of²³⁵U was also estimated by neutron activation analysis. The experimental results are compared with the calculated ones.     

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.     

Interference from uranium in neutron activation analysis or rare-earths in silicate rocks

A direct nondestructive method of analysis for²⁴¹Am utilizing photon counting and self-absorption correction factors is presented. The method gives favorable agreement for samples analyzed by radiochemical separation procedures and alpha particle spectrometry. The comparison was made over a range of approximately five orders of magnitude of²⁴¹Am concentrations. The method is reliable and relatively simple. Sensitivity for a ∼5-g sample and a counting intervals of 60 000 s is ∼0.2 pCi/g with an uncertainty of ±22%, which decreases to ±11% for increased counting intervals of 150 000 s and an increased sample size of ∼20 g.