Syntheses, Structures, and Spectroscopic Properties of Plutonium and Americium Phosphites and the Redetermination of the Ionic Radii of Pu(III) and Am(III)

A series of isotypic rare earth phosphites (RE = Ce(III), Pr(III), Nd(III), Pu(III), or Am(III)) with the general formulas RE(2)(HPO(3))(3)(H(2)O) along with a Pu(IV) phosphite, Pu[(HPO(3))(2)(H(2)O)(2)], have been prepared hydrothermally via reactions of RECl(3) with phosphorous acid. The structure of RE(2)(HPO(3))(3)(H(2)O) features a face-sharing interaction of eight- and nine-coordinate rare earth polyhedra. By use of the crystallographic data from the isotypic series along with data from previously reported isotypic series, the ionic radii for higher coordinate Pu(III) and Am(III) were calculated. The (VIII)Pu(III) radius was calculated as 1.112 ± 0.004 ?, and the (IX)Pu(III) radius was calculated to be 1.165 ± 0.002 ?. The (VIII)Am(III) radius was calculated as 1.108 ± 0.004 ?, and the (IX)Am(III) radius was calculated as 1.162 ± 0.002 ?.     

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.     

Determination of plutonium,americium and curium in environmental meterials

A sequential radiochemical scheme for the separation of Pu and Am (along with Cm) from environmental materials is given. Optimum conditions for coprecipitation of these elements on bismuth phosphate and the influence of Fe and Th content of the sample on the recovery of Am were studied. Internal tracers²⁴²Pu and²⁴³Am were used as tracers for Pu and Am, respectively, and estimates were made by alpha-spectrometry. Average recoveries obtained from sea water were 85% and 77% for Pu and Am, respectively. Lower recoveries (<50%) were obtained for Am in sediments. Work carried out as part of the International Atomic Energy Agency Research Contract 1954/RB/RI.     

Quantum chemical calculations of the redox potential of the Pu(VII)/Pu(VIII) couple

The redox potential of the Pu(VII)/Pu(VIII) couple was studied by density functional theory calculations. The spin-orbit effect was corrected at the CASSCF level. The redox potential (relative to the standard hydrogen potential) of the Pu(VII)/Pu(VIII) couple in alkaline solution was found to vary from 4.36 to 1.06 V depending on the number of Pu-O oxo bonds, coordination numbers, and coordination modes. The redox potential drops substantially as the number of Pu-O oxo bonds increases. Pu(VIII) may be synthesized in strong alkaline solution assuming that both Pu(VII) and Pu(VIII) exist in penta-oxo form, Pu (VII)O 5OH (4-) and Pu (VIII)O 5OH (3-), respectively. The Mulliken population of Pu in Pu(VII) and Pu(VIII) complexes are very similar, suggesting that the spin-orbit effect is rather small in Pu(VII) complexes and that when Pu(VII) is oxidized to Pu(VIII) the electron is stripped mainly from the ligand. Consequently, Pu(VIII) is in an unstable oxidation state and easily reduced back to Pu(VII) by the solvent water molecules. In acidic medium, the Pu(VII)/Pu(VIII) redox potential is too high to get the Pu(VIII) valence state.     

Simultaneous determination of plutonium and americium in soils by extraction chromatography

A radiochemical method is described for the determination of²³⁸Pu,^239(240)Pu and²⁴¹Am in a single soil sample. Plutonium is separated from a HNO₃ leaching solution by a Microthene-TNOA column; amcricium is coprecipitated by oxalic acid, decontaminated from polonium by a TNOA-column in HCl medium, separated from the rare earth elements by a Microthene-HDEHP column, eluted with a 0.07M DTPA+1M lactic acid solution and finally purified by a PMBP-TOPO extraction. The method supplies a good decontamination of Am and Pu from natural alpha emitters; starting from 50 g soil, the average yields were 75.1±13.4% for plutonium and 57.7±10.8% for Am.^239(240)Pu,²³⁸Pu and²⁴¹Am concentrations (mBq/kg) in three different kinds of soil were the following: 255, 10.4, 81.3 (uncultivated soils); 236, 11.6, 76.7 (cultivated soils); 46, 1.9, 19.8 (river sediment). The average ratios²³⁸Pu to^239(240)Pu and²⁴¹Am to^239(240)Pu were 0.044 and 0.350, respectively.     

Study of the interferences in the determination of Pu, Am and Cm in radioactive waste by extraction chromatography

This paper describes the experimental studies carried out to determine (238)Pu, (239/40)Pu, (241)Pu, (241)Am, (242)Cm and (244)Cm in samples from nuclear power plants (mainly spent ion exchange resins and evaporator concentrates) using an organophosphorus compound immobilized on an inert support. These materials are commercially available under the name TRU Resin (for Transuranium Specific) from Eichrom Industries, Darien, IL. An attempt is made to develop a rapid, accurate method of analysis, with minimum waste generation. Standard solutions of Pu and Am and one sample of spent ion exchange resin that contains fission, activation products, Pu, Am and Cm were analyzed to study the separation factors and interferences in the measurement of Pu, Am and Cm isotopes.     

A Rapid Fecal Bioassay Method for Pu/Am

Fecal radiobioassay is a sensitive tool to estimate intake of radionuclides, especially for insoluble or poorly absorbed actinides. To increase efficiency and reduce turnaround time, improvements were introduced in the sample digestion step of a fecal bioassay method to rapidly detect Pu and Am. The acid- and microwave-digestion of the spiked fecal samples (5–10 g) were effectively completed in 1 h. The turnaround time for the sample analysis was minimized to 6 h. The average recoveries for Pu and Am were 35% and 60% for artificial fecal samples, respectively. Much better recoveries for Pu and Am were obtained for natural fecal samples. Observed relative biases for Pu and Am were marginally in the range of -0.25 to +0.50. The relative precision values for both radionuclides were, however, within the performance index of 0.4. This rapid fecal method is a potential candidate for an acceptable quantitative radiobioassay and screening method for the suspected Pu/Am exposures.     

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%.     

Age determination of single plutonium particles after chemical separation

Age determination of single plutonium particles was demonstrated using five particles of the standard reference material, NBS 947 (Plutonium Isotopic Standard. National Bureau of Standards, Washington, D.C. 20234, August 19, 1982, currently distributed as NBL CRM-137) and the radioactive decay of ²⁴¹Pu into ²⁴¹Am. The elemental ratio of Am/Pu in Pu particles found on a carbon planchet was measured by wavelength dispersive X-ray spectrometry (WDX) coupled to a scanning electron microscope (SEM). After the WDX measurement, each plutonium particle, with an average size of a few μm, was picked up and relocated to a silicon wafer inside the SEM chamber using a micromanipulator. The silicon wafer was then transferred to a quartz tube for dissolution in an acid solution prior to chemical separation. After the Pu was chemically separated from Am and U, the isotopic ratios of Pu (²⁴⁰Pu/²³⁹Pu, ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu) were measured with a thermal ionization mass spectrometer (TIMS) for the calculation of Pu age. The age of particles determined in this study was in good agreement with the expected age (35.9 a) of NBS 947 within the measurement uncertainty.     

Radioanalytical approach to determine 238Pu, 239+240Pu, 241Pu and 241Am in soils

The simultaneous determination of multiple actinide isotopes in samples where total quantity is limited can sometimes present a unique challenge for radioanalytical chemists. In this study, re-determination of ²³⁸Pu, ^239+240Pu, and ²⁴¹Am for soils collected and analyzed approximately three decades ago was the goal, along with direct determination of ²⁴¹Pu. The soils had been collected in the early 1970’s from a shallow land burial site for radioactive wastes called the Subsurface Disposal Area (SDA) at the Idaho National Lab (INL), analyzed for ²³⁸Pu, ^239+240Pu, and ²⁴¹Am, and any remaining soils after analysis had been archived and stored. We designed an approach to reanalyze the ²³⁸Pu, ^239+240Pu, and ²⁴¹Am and determine for the first time ²⁴¹Pu using a combination of traditional and new radioanalytical methodologies. The methods used are described, along with estimates of the limits of detection for gamma-and alpha-spectrometry, and liquid scintillation counting. Comparison of our results to the earlier work documents the ingrowth of ²⁴¹Am from ²⁴¹Pu, and demonstrates that the total amount of ²⁴¹Am activity in these soil samples is greater than would be expected due to ingrowth from ²⁴¹Pu decay.     

Half-life of plutonium-241: Past and present

Half-life of²⁴¹Pu is of great importance in nuclear technology. In view of large variation in the values (13–15 y) reported till 1974 in literature, efforts have been made in different laboratories to determine this half-life with high precision and accuracy. In our laboratory, it has been determined by different methods which may be classified in two categories, viz. (1) parent decay method, and (2) daughter growth method. In the parent decay method, change in isotope ratios²⁴¹Pu/²³⁹Pu,²⁴¹Pu/²⁴⁰Pu and²⁴¹Pu/²⁴²Pu was studied periodically by a thermal ionization mass spectrometer. Single as well as double ratio method was used to calculate the half-life. In the daughter growth method, the half-life was obtained in four independent ways. These were (1) alpha spectrometry taking²³⁹Pu and²⁴²Pu separately as reference isotopes and studying periodically the increase in alpha activity ratio, (2) alpha proportional counting for observing periodically the change in total alpha activity, (3) isotope dilution alpha spectrometry using²⁴³Am as a spike, (4) isotope dilution mass spectrometry using²⁴³Am as a spike. In all these methods, synthetic mixtures were prepared for achieving high precision and accuracy in different measurements. Based on the results obtained in this laboratory and the values reported by other laboratories, a half-life value of 14.4±0.1 y is recommended. The paper reviews the past history, puts forth the present status, highlights the current trends for studying the effect of chemical composition of plutonium on the half-life of²⁴¹Pu and presents the future requirements for achieving higher accuracy in the half-life of²⁴¹Pu.     

Determination of activity concentrations and activity ratios of plutonium,americium and curium isotopes in radioactive waste samples

This paper presents a rapid and quantitative radiochemical separation method for the Pu, Am and Cm isotopes with an anion exchange resin and a TRU resin. After the Pu isotopes were purified with an anion exchange resin method and the Am and Cm isotopes were purified with the TRU resin method, micro-coprecipitation method was applied for an alpha-source preparation. The activity concentrations and activity ratios for the Pu, Am and Cm isotopes in a radioactive sample were measured by radiation counting methods such as an alpha-spectrometry and a liquid scintillation counting as well as by a mass spectroscopic method such as a thermal ionization mass spectrometry.     

Extraction and stripping behavior of U–Np–Tc ternary system to TBP

Stripping of the nuclides U, Np, Pu, Am, Eu, Zr, Ru and Fe from the loaded TRUEX solvent (0.2M CMPO+1.2M TBP in dodecane) has been carried out with a potassium ferrocyanide solution. In four contacts, 98% or more of U, Pu, Am and Eu could be stripped whereas Zr and Ru recoveries were 94% and 92%, respectively. Further, the co-precipitation of Am, Pu, U and Eu on ferric ferrocyanide precipitate from the CMPO phase has shown high recovery of Am, Pu and Eu but lower for U.     

Concentration and vertical distribution of plutonium and americium in Italian mosses and lichens

The plutonium and americium concentration and vertical distribution in some Italian mosses and lichens have been determined. The^239,240Pu,²³⁸Pu and²⁴¹Am concentration ranges in tree trunk lichens 0.83–1.87, 0.052–0.154 and 0.180–0.770 Bq/kg, respectively. The corresponding values in tree mosses are higher and more scattered ranging from 0.321 to 4.96, from 0.029 to 0.171 and from 0.200 to 1.93 Bq/kg. The mean²³⁸Pu/^239,240Pu and²⁴¹Am/^239,240Pu ratios are 0.088±0.037 and 0.38±0.13 in lichens and 0.091±0.072 and 0.54±0.16 in tree mosses. The Pu and Am concentrations are relatively low in terrestrial mosses. The^239,240Pu,²³⁸Pu and²⁴¹Am vertical distributions in a terrestrial moss core (Neckera Crispa) collected near Urbino (central Italy) show an exponential decrease with the height. On the contrary the²⁴¹Am vertical distribution in another terrestrial moss core (Sphagnum Compactum) collected in the Alps (northern Italy) shows an interesting peak at 16 cm which corresponds to the deposition of fallout from the nuclear weapon tests in 1960's. The²⁴¹Am movement upward and downward in the moss core is also studied. The results show once again that both mosses and lichens are very effective accumulators of Pu and Am and that they can be used as good biological indicators of the radionuclide airbome pollution from nuclear facilities and nuclear weapon tests. They can play a very impotant role in cycling naturally or artificially enhanced radionuclides in the atmosphere over long time scales.     

The application of column redox-extraction chromatography to the separation of some actinide elements

The application of a new technique to the separation of some actinide elements by means of a single reducing and extracting column is described. Tri-n-octylphosphine oxide (TOPO) was used as the extractant. The following reducing agents were supported on microporous polyethylene together with TOPO: tetrachlorohydroquinone, 2,3-dichloro-1,4-naphthahydroquinone, 2,5-di-tert-butylhydroquinone and 2,5-di-tert-pentylhydroquinone. The last compound was chosen for the separation experiments; it allowed quantitative reduction of plutonium to Pu(III) and of neptunium to Np(IV). The separations Pu(III)-Np(IV), Pu(III)-U(VI) and Am(III)-Np(IV) in 6 M hydrochloric acid were obtained.     

Pu and Am sorption to the Baltic Sea bottom sediments

Sorption of Am and Pu isotopes to bottom sediments of the Baltic Sea has been studied under natural and laboratory conditions. Data obtained from sequential extraction, sorption of Am(III), Pu(IV) and Pu(V) as well as oxidation state distribution experiments have shown that Pu(V) sorption mechanism includes a very fast Pu(V) reduction (reaction rate ≤ 2.33 × 10^?3 s^?1) to Pu(IV) by humic substances and/or by Fe(II) to Pu(IV) and partly to Pu(III). Following reduction Pu isotopes were bound to various components of bottom sediments via ion exchange and surface complexation reactions and a slow incorporation into the crystalline structure of Fe minerals. Kinetics experiments showed that the sorption of Pu(V), Pu(IV) and Am(III) to bottom sediments from natural seawater was controlled by the inert layer diffusion process.     

Accurate purification age determination of individual uranium–plutonium mixed particles

Age of individual uranium–plutonium (U/Pu) mixed particles with various U/Pu atomic ratios (1–70) were determined by inductively coupled plasma mass spectrometry. Micron-sized particles were prepared from U and Pu certified reference materials. The Pu reference was stored for 4–6 years since the last purification (July 14, 2008). The Pu purification age was obtained from the ²⁴¹Am/²⁴¹Pu ratio which was calculated from the product of three measured ratios of Pu and Am isotopes in the eluted fractions. These ratios were measured by a high-resolution inductively coupled plasma mass spectrometer equipped with a desolvation system. Femto-gram to pico-gram quantities of Am, U, and Pu in a sample solution were sequentially separated on a small anion-exchange column. The ²⁴¹Am/²⁴¹Pu ratio was accurately determined by spiking pure ²⁴³Am into the sample solution. The average determined age for the particles for the five independent U/Pu ratios was in good agreement with the expected age with high accuracy (difference age 0.27 years) and high precision (standard deviation 0.44 years). The described analytical technique can serve as an effective tool for nuclear safeguards and environmental radiochemistry.

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Figure Young (4?6 y) Pu purification age of individual U/Pu mixed micron-sized reference particles for the five independent U/Pu ratios (1?70) were determined with 0.27±0.44 y difference from the expected age. Sub pico-gram quantities of Am, U and Pu were sequentially separated a small column, and their isotope ratios were accurately measured using an ICP-MS by applying the ²⁴³Am spiking technique to the analysis and correcting the impurity and the contaminations.

     

Isotopic analysis of plutonium using a combination of alpha and internal conversion electron spectroscopy

A combination alpha and conversion electron spectrometer was developed to quantify ²³⁹Pu/²⁴⁰Pu and ²³⁸Pu/²⁴¹Am isotopic ratios of plated sources. The spectrometer was constructed with a commercially available low noise passivated ion-implanted planar silicon (PIPS) detector that was cooled to 77 K with liquid nitrogen. The combination spectrometer was used to quantify alpha-particles, conversion electrons, gamma-rays and X-rays associated with the decay of various plutonium isotopes and ²⁴¹Am. Two amplifiers operated in parallel with different gains allowed for simultaneous acquisition of the lower energy region (21-60 keV) for internal conversion electrons, gamma-rays and X-rays, and the higher energy region (5050 keV-5550 keV) for alpha-particles. Energy resolutions of 2.2 keV FWHM (full-width at half maximum) for the 38.7 keV M conversion electrons and 11.2 keV for the 5499.2 keV alpha-particles from ²³⁸Pu were measured. The energy resolution combined with a spectral deconvolution method was sufficient to be able to quantify the radioactivity using the alpha-spectra as well as the electron spectra; however, quantification of the radioactivity using the internal conversion electron spectra was more problematic because of the presence of X-rays, gamma-rays, Compton scatter electrons and the number of electron peaks present. Deconvolution of the alpha-spectra yielded ²³⁹Pu and ²⁴⁰Pu activities (as % of total Pu activity), which differed from expected values by -3.0% to 5.4%. Deconvolution of an internal conversion electron spectrum of a high ²³⁹Pu and low ²⁴¹Am activity sample yielded ²³⁹Pu and ²⁴⁰Pu activities, which differed by -17.1 and -35.5% relative to the alpha-measurements, respectively. Determination of the Pu activity using the electron spectra was more problematic in samples where the ²⁴¹Am activity dominated. Determination of ²³⁸Pu and ²⁴¹Am activity by the electron spectroscopy data was also obtained and compared with the alpha-spectroscopy results. Theoretical investigation of the removal of ²⁴¹Am or use of a 400 eV electron spectrometer indicated that the internal conversion electron spectra could be used to determine the ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu/²⁴¹Am (when present) activity with and without spectral deconvolution, respectively.     

Radiochemical separation of Pu, U, Am and Sr isotopes in environmental samples using extraction chromatographic resins

This study presents a rapid and quantitative sequential radiochemical separation method for Pu, U, Am and Sr isotopes in environmental samples with extraction chromatographic resins. After radionuclides were leached from the samples with 6 M HNO₃, Pu and U isotopes were adsorbed onto the UTEVA column and Am isotopes were adsorbed onto the TRU column connected with the UTEVA column. Also, ⁹⁰Sr was adsorbed onto the Sr column connected with the TRU column. Pu and U isotopes were purified from other nuclides through the UTEVA column. In addition, Am isotopes were separated from other nuclides with the TRU column. Finally, ⁹⁰Sr was purified with the Sr resin. After α source preparation for the purified Pu, U and Am isotopes with micro-coprecipitation method, Pu, U and Am isotopes were measured using alpha spectrometry. On the other hand, ⁹⁰Sr was measured using a low level liquid scintillation counter. The radiochemical procedure for Pu, U, Am and Sr nuclides investigated in this study has been applied to environmental samples after validating the simulated samples.     

137Cs, 40K, 90Sr, 238, 239+240Pu, 241Am and 243+244Cm in forest litter and their transfer to some species of insects and plants in boreal forests: Three case studies

Results for ¹³⁷Cs, ⁴⁰K, ⁹⁰Sr, ^238,239+240Pu, ²⁴¹Am and ^243+244Cm measurements in plant, insects and forest litter samples collected at three sites in Poland are presented. New results are compared with some existing data for locations examined during previous studies. Insect samples were introduced now for the first time. Relatively high activities of ⁹⁰Sr were noticed for spruce bark beetle (Ips typographus) and those for ¹³⁷Cs, plutonium and ²⁴¹Am for forest dung beetle (Anoplotrupes stercorosus). Faster than caused by physical decay decrease of radiocesium activity was noticed for the majority of plant and litter samples. The results for ^239+240Pu for litter were similar to previous results, but the activities of ²³⁸Pu were smaller. The activity ratio between ²⁴¹Am and ^239+240Pu was found lower than expected for known proportions between global and Chernobyl fallout. Thus a kind of dynamic behavior of Pu and Am in the forest ecosystem is concluded. Transfer factors and aggregation coefficients were estimated and discussed for both plants and insects as well as between insects and the part of plants (or litter) they feed on. Many of them were never presented before.The authors are thankful to the Polish State Committee for Scientific Research for financial support of this investigation, Grant No. PG04 07520.