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.     

Radiological responses of different types of Egyptian Mediterranean coastal sediments

The aim of this study was to identify gamma self-absorption correction factors for different types of Egyptian Mediterranean coastal sediments. Self-absorption corrections based on direct transmission through different thicknesses of the most dominant sediment species have been tested against point sources with gamma-ray energies of ²⁴¹Am, ¹³⁷Cs and ⁶⁰Co with 2% uncertainties. Black sand samples from the Rashid branch of the Nile River quantitatively absorbed the low energy of ²⁴¹Am through a thickness of 5 cm. In decreasing order of gamma energy self-absorption of ²⁴¹Am, the samples under investigation ranked black sand, Matrouh sand, Sidi Gaber sand, shells, Salloum sand, and clay. Empirical self-absorption correction formulas were also deduced. Chemical analyses such as pH, CaCO₃, total dissolved solids, Ca²⁺, Mg²⁺, CO₃^2?, HCO₃^? and total Fe²⁺ have been carried out for the sediments. The relationships between self absorption corrections and the other chemical parameters of the sediments were also examined.     

Preliminary investigation on biosorption mechanism of 241Am by Rhizopus arrhizus

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. Encouraging biosorption of ²⁴¹Am from aqueous solutions by free or immobilized Rhizopus arrhizus (R. arrhizus) has been observed in our experiments. In this study, the preliminary evaluation on the mechanism was further explored via chemical or biological modification of R. arrhizus using europium as a substitute for americium. The results indicated that in approximately 48 hours R. arrhizus was able for efficient adsorption of ²⁴¹Am. The pH value of solutions decreased gradually with the uptake of ²⁴¹Am by R. arrhizus, implying that H⁺ was released from R. arrhizus via ion-exchange. The biosorption of ²⁴¹Am by the decomposed cell wall of R. arrhizus was as efficient as by the intact fungus. The adsorption ratio for ²⁴¹Am by deacylated R. arrhizus dropped, implying that carboxyl functional groups of R. arrhizus play an important role in the biosorption of ²⁴¹Am. Most of the investigated acidic ions have no significant influence on the adsorption of ²⁴¹Am, while saturated EDTA can strongly inhibit the biosorption of ²⁴¹Am by R. arrhizus. When the concentrations of coexistent Eu³⁺, Nd³⁺ were 300 times more than that of ²⁴¹Am, the adsorption ratios would decrease to about 86% from more than 99%. It could be noted by transmission electron microscope (TEM) analysis that the adsorbed Eu is scattered almost in the whole fungus, while Rutherford backscattering spectrometry (RBS) indicated that Ca in R. arrhizus have been replaced by Eu via ion-exchange. The change of the absorption peak structure in the IR spectra implied that there was complexation between metals and microorganism. The results implied that the adsorption mechanism of ²⁴¹Am by R. arrhizus is very complicated involved ion-exchange, complexation process as well as nonspecific adsorption in the cell wall by static electricity.     

Sorption of 241Am by Aspergillus nigerspore and hyphae

Biosorption of ²⁴¹Am by a fungus A. niger, including the spore and hyphae, was investigated. The preliminary results showed that the adsorption of ²⁴¹Am by the microorganism was efficient. More than 96% of the total ²⁴¹Am could be removed from ²⁴¹Am solutions of 5.6-111 MBq/l (C _o) by spore and hyphaeof A. niger, with adsorbed ²⁴¹Am metal (Q) of 7.2-142.4 MBq/g biomass, and 5.2-106.5 MBq/g, respectively. The biosorption equilibrium was achieved within 1 hour and the optimum pH range was pH 1-3. No obvious effects on ²⁴¹Am adsorption by the fungus were observed at 10-45 °C, or in solutions containing Au³⁺ or Ag⁺, even 2000 times above the ²⁴¹Am concentration. The ²⁴¹Am biosorption by the fungus obeys the Freundlich adsorption equation. There was no significant difference between the adsorption behavior of A. nigerspore and hyphae. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

A partial body counter for incorporated low level actinides

A new partial body counter has been installed and calibrated at the Institute of Radiation Hygiene of the Federal Office for Radiation Protection, Munich, Bavaria. The system is especially designed for radionuclides emitting low energy photons such as²⁴¹ Am and²¹⁰Pb. In addition, thorium, uranium and daughter products,⁶⁰Co,¹³⁷Cs and⁴⁰K can be detected. The main components of the system are a shielding chamber, 4 high purity low-energy germanium detectors with beryllium windows and the corresponding electronics and software. A LLNL Realistic Phantom is used to calibrate the system. Inactive organs and organs loaded with a known amount of²⁴¹Am (right lung, left lung, liver) are available to quantify the response of each detector separately. Detector efficiencies are given as function of chest wall thickness (1.7 to 3.4 cm). Lower limits of detection for²⁴¹Am using a measurement time of 3600 seconds are 6, 7 and 7 Bq for right lung, left lung and liver, respectively. In order to estimate skeleton activities, a skull phantom loaded with²⁴¹Am is available. For one detector, the lower limit of detection for the skull is 2 Bq.     

Application of the multiple isotope material basis set (MIMBS) method of isotope identification to low energy gamma emitters

The multiple isotope material basis set (MIMBS) method for isotope identification combines the material basis set (MBS) model of gamma spectrum attenuation with ordinary response function fitting to identify shielded gamma-emitting isotopes, using low and medium resolution gamma detectors such as NaI and LaBr₃. Although MIMBS has been shown to outperform conventional isotope identification algorithms that do not correct for attenuation effects, it has difficulty identifying low energy emitters such as ⁵⁷Co or ²⁴¹Am. In this article we examine the use of optimized multiple attenuator thicknesses in generating basis spectra for each isotope to obtain better modeling of the low energy spectrum while simultaneously extending the range of the model to thicker attenuators. The effectiveness of the multiple thickness MIMBS algorithm in improving isotope identification rates compared with the original MIMBS method is demonstrated with analyses of simulated gamma spectra. The identification rates obtained with the MIMBS methods are compared to those obtained using the commercial peak-based ScintiVision NaI analysis software.     

The separation of241Am from bones by coprecipitation with bismuth phosphate

The conditions of²⁴¹Am separation from bone by coprecipitation with BiPO₄ were studied. It was found that by coprecipitation with BiPO₄ ²⁴¹Am can be separated with high yield from different amount of bone. The main condition of the achievement of a high yield is a low Fe/III/ concentration in solution at americium coprecipitation.     

Separation of241Am from urine and feces by coprecipitation with BiPO4

The conditions of²⁴¹Am separation from urine and feces by coprecipitation with BiPO₄ were studied. It was found that by coprecipitation with BiPO₄ ²⁴¹Am can be separated with high yield from urine. The yield of separation from feces is diminished due to the presence of Fe.     

Kinetics of americium and europium extraction by tert-butylthiacalix[4]arene from alkaline media

Kinetics of ¹⁵²Eu and ²⁴¹Am extraction by nitrogen-bearing alkyl amino phenol oligomer YaRB and tert-butylthiacalix[4]arene TCA from carbonate-alkaline media was studied. Both extractants efficiently extract americium and europium in pH interval 12–14. The maximum of americium extraction is located at the lower values of pH, compared with europium. YaRB extracts americium and europium faster than TCA, and at the same time, americium is extracted faster than europium by both extractants. In general, thiacalixarene TCA is regarded as more efficient extractant than alkyl amino phenol oligomer YaRB.

     

Determination of 241Am in Environmental Samples: A Review

The determination of ²⁴¹Am in the environment is of importance in monitoring its release and assessing its environmental impact and radiological risk. This paper aims to give an overview about the recent developments and the state-of-art analytical methods for ²⁴¹Am determination in environmental samples. Thorough discussions are given in this paper covering a wide range of aspects, including sample pre-treatment and pre-concentration methods, chemical separation techniques, source preparation, radiometric and mass spectrometric measurement techniques, speciation analyses, and tracer applications. The paper focuses on some hyphenated separation methods based on different chromatographic resins, which have been developed to achieve high analytical efficiency and sample throughput for the determination of ²⁴¹Am. The performances of different radiometric and mass spectrometric measurement techniques for ²⁴¹Am are evaluated and compared. Tracer applications of ²⁴¹Am in the environment, including speciation analyses of ²⁴¹Am, and applications in nuclear forensics are also discussed.     

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene

Polypropylenimine dendrimer (DAB‐Am‐32, generation 4.0) was converted into a macroinitiator DAB‐Am‐32‐Cl via reaction with 2‐chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH₂)₃₂‐polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB‐Am‐32‐Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, ¹H NMR, and ¹³C NMR. The structure of poly(propylene imine)(NH₂)₃₂‐polystyrene was characterized by FT‐IR spectrum and ¹H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH₂)₃₂‐polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30–80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB‐Am‐32‐Cl, the number‐average diameter (D_n), weight‐average diameter (D_w) were both increased gradually. With enhancing the surfactant concentration, the measured D_h of the nanoparticles decreased, while the polydispersity increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892–2904, 2009     

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.     

Americium(III) sorption from multicomponent solutions by macrocyclic polyester-based sorbents

Americium sorption by crown-ether-impregnated polymeric sorbents from nitric acid solutions and multicomponent nitrate solutions that model process solutions was studied. Sorption of ballast elements by the unimpregnated Porolas-T support was studied. The sorption coefficients K _d of these elements on Porolas-T do not exceed 0.01. Sorption of the same elements by crown-ether-impregnated sorbents was also studied. Dicyclohexano-18-crown-6 (DCH18C6) and its alkyl derivatives were used. Sorption coefficients were determined for all ballast elements. At the final stage of the study, ²⁴¹Am sorption coefficients of from multi-component solutions were determined. The data obtained signify the utility of crown-ether-impregnated sorbents for recovering ²⁴¹Am from multicomponent technological solutions.     

Contribution of an interlaboratory comparison to the certification of the STAM/IRMM-0243 243Am reference material

Following the expression of the need for an americium (Am) standard and particularly for one with a certified americium-243 (²⁴³Am) content, the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA)/Direction de l’Energie Nucléaire of Marcoule and the European Commission Joint Research Center in Geel carried out a collaborative project for the production of a certified reference material enriched in ²⁴³Am. CEA’s Commission d’ETAblissement des Méthodes d’Analyse organized an interlaboratory comparison on this material prior to the issuing of its certificate. The usefulness of an interlaboratory comparison to assess the measurement capabilities in the field and to confirm the provisional certified values for the amount contents of ²⁴³Am, ²⁴¹Am, total Am, the isotopic composition and the molar mass of Am has been demonstrated. Furthermore this interlaboratory comparison enabled to derive an indicative value for the n(^242mAm)/n(²⁴³Am) isotope amount ratio.

     

Design of experiments in 241Am alpha source preparation by electrodeposition: an approach to process optimization

This work describes a procedure to improve the quality of an ²⁴¹Am alpha source obtained by means of electrodeposition. The technique of design of experiments (DoE) was applied in order to perform a multivariate analysis of the experimental variable effects taking into consideration the following: i—amperage, d—cathode–anode distance, t—time and PP—polishing process. A 3⁴⁻² fractional design was employed using four experimental factors, three levels per factor, and three response variables were studied: H_area = electrodeposited active area, %R = activity recovery percentage, and Δ_1/2 = width at half-height. Thanks to this simple design, 9 experiments were enough, done in triplicate, to discern how Δ_1/2 and %R are modified when experimental factors change. Additionally, this work provides tools to perform effect statistical analysis of experimental factors, and to pose linear models applying significant terms. The models obtained were validated by analysis of variance and they were of help to verify the choice of significant factors by means of DoE and to approximate to the optimization of the preparation method of a ²⁴¹Am alpha source by means of contour plots of Δ_1/2 and %R.

     

Removal of 90Sr and 241Am from concentrated Hanford chelate-bearing waste by precipitation with strontium nitrate and sodium permanganate

The Hanford Nuclear Site, near Richland, Washington, is developing a method to simultaneously remove chelated ⁹⁰Sr and ²⁴¹Am from the liquid phase of high-level nuclear waste using sodium permanganate and cold strontium nitrate. This method has been reported previously for treating diluted waste in the Hanford Waste Treatment and Immobilization facility (WTP) that is currently under construction. This method had not been verified previously for treating the more concentrated waste as it sits in the tank farm. There are a number of logistical advantages to performing this process in the tank farm. Therefore, the present study was undertaken to compare the removal of ⁹⁰Sr and ²⁴¹Am in diluted waste (WTP conditions) and more concentrated waste (tank farm conditions). Both diluted and more concentrated waste from Hanford tank AN-107 was treated with 3.0 M Sr(NO₃)₂ and 3.8 M NaMnO₄, at a constant cold chemical to radionuclide ratio. The amount of ⁹⁰Sr and ²⁴¹Am removed was monitored through alpha and beta counting. The removal of ⁹⁰Sr was essentially identical at both levels of dilution. The removal of ²⁴¹Am was slightly better in the diluted sample than in the tank farm sample, but the difference was not large (77 % versus 67 % removed). These results indicate that it is reasonable to expect this ⁹⁰Sr and ²⁴¹Am removal process can be employed in the tank farm.     

Rotational isomerism—XII Rotamer energies and 3JHF and 4JHH couplings in 1-chloro-2-bromo-2-fluoropropane (1)

The complete analysis of the NMR spectrum of CH₂Cl.CFBr.CH₃ in CCl₄ and acetone is given. The long range ⁴J_HH couplings in this molecule differ considerably and surprisingly are both positive. An analysis of the solvent dependence of the couplings enables the rotamer couplings and energies to be obtained. The rotamer energies and their variation with solvent are in accord with quantitative predictions and results from similar halogenated ethanes. The values of the ⁴J_HH couplings can be rationalised in terms of substituent electronegativity effects.     

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.