International program to improve decay data for transactinium nuclides

To help meet an identified need for precise decay data, in 1977 the IAEA organized an international Coordinated Research Program (CRP) to measure and evaluate half-lives and γ- and α-emission probabilities for selected transactinium nuclides of importance for reactor technology. The CRP goals were (1) to determine a list of data that needed improvement, (2) to encourage new measurements, and (3) to evaluate the available data. All three phases of this work are now complete. Our participation in this effort has involved the measurement of γ-ray emission probabilities for ^232,233,235U, ^{238,239,240,241}Pu, ²²⁹Th and ²³³Pa, as well as participating in the data evaluation. The γ-emission probabilities were determined from the measurement of γ-emission rates with the goal of obtaining uncertainties of ≤ 1%. γ-measurements were made on calibrated Ge detectors. These calibrations were done by standard methods, generally involving measurements at ∼ 60 γ-ray energies from 14 to 2700 keV. The efficiency-calibration functions were assigned uncertainties ranging from 2% below 50 keV to 0.50% from 400 to 1400 keV. The determination of the decay rates of the various sources involved several techniques. The ²³⁸Pu, ²³⁹Pu and ²⁴⁰Pu samples were calibrated by gross α-emission-rate measurements at NBS. The ²³⁵U sample was taken from an NBS-calibrated spike solution. The ²⁴¹Pu and ²³³U samples were calibrated by isotope-dilution mass spectrometry based on spikes of the calibrated ²³⁹Pu, ²⁴⁰Pu and ²³⁵U materials. Some of our results are given, together with a comparison of some present and previous results.     

Determination of the isotope composition and content of U and Pu in environmental samples on the ultrasmall level by isotope dilution mass spectrometry

A procedure was developed for isolation and determination of the isotope composition and content of U and Pu on the ultrasmall level in environmental samples of technogenic origin, characterized by a small mass (up to 0.l g) and complex macrocomposition. The procedure is based on isotope dilution and mass-spectrometric measurement of the isotope ratios (IDMS). Subnanogram quantities of U and Pu were isolated using a modification of resin bead technique, involving sorption on a limited number of anion exchanger beads and allowing, after desorption, analysis of the solutions containing the selectively isolated nanogram quantities of U or 10^–12–10^–15 g of Pu. The measurements were carried out on thermal ionization mass spectrometers manufactured in Ukraine and Russia with a modernized ion registration system utilizing a position-sensitive detector based on microchannel plates. Uranium was analyzed by the laser luminescence method suitable for measuring fractions of nanograms of U accurately to within 10%. This procedure, combining highly sensitive methods of isolation of ultrasmall quantities of U and Pu with the mass-spectrometric method of analysis, is applied at the Radium Institute (acting as a national laboratory of IAEA) and at the Institute of Analytical Instrument Designing, Russian Academy of Sciences, in analysis of inspection samples submitted by IAEA for monitoring the activity of nuclear facilities under the Treaty on Nonproliferation of Nuclear Weapons.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 464–470.Original Russian Text Copyright © 2004 by Stepanov, Makarova, Domkin, Pevtsova, Aleksandruk, Nikolaeva, Chubinskii-Nadezhdin, Kulikov.     

Plutonium isotopes in marine sediments and some biota from the Sudanese coast of the Red Sea

Measurements of (239+240)Pu and (238)Pu were carried out on marine biota as well as on sediments from the fringing reefs area extending towards north and south (Flamingo Bay) of PortSudan harbour. The analyses were performed using radiochemical separation and alpha spectrometry. The range of the activity concentrations in marine sediments, in mBq kg(-1) dry weight, was found to be from 5.10 to 82.00 for (239+240)Pu and from 0.89 to 8.63 for (238)Pu. Corresponding activity concentrations of (239+240)Pu and (238)Pu in sediments from the harbours at PortSudan and Sawakin were 53-301 and 8.29-28.6 (PortSudan) and 163-343 and 4.7 (Sawakin), respectively. The higher values for plutonium in marine algae suggest their suitability as an indicator species for monitoring purposes. The results obtained are generally lower than those found by other studies and show that the Red Sea environment is mildly affected by plutonium contamination. Activity ratios of plutonium isotopes confirm that the existence of plutonium in the Red Sea is mainly due to atmospheric global fallout.     

A Method for Determining the Isotope Composition of U, Pu, Am, and Cm in "Hot" Particles and Spent Nuclear Fuel

A method was proposed for determining the content of ^234-238U, ^238-242Pu, ^241-243Am, and ^242-244Cm in "hot" fuel particles and spent nuclear fuel. The method is based on high-precision measurement of the -activity in the sample and calculation of the relative contributions of individual nuclides or radionuclide groups to the total activity. Partitioning of U, Pu, Am, and Cm was carried out by ion-exchange chromatography. The contents of ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ^239+240Pu, ²⁴²Pu, ²⁴¹Am, ^242mAm, ²⁴³Am, ²⁴²Cm, and ²⁴⁴Cm in "hot" particles sampled in the Chernobyl area were reported. The applicability of the method proposed to determining the radionuclide composition of spent nuclear fuel was discussed.     

高放废物中^238Pu,^240Pu,^242Pu在聚变—裂变混合堆内的嬗变研究

从中子学角度研究了高放废物中２３８Ｐｕ、２４０Ｐｕ、２４２Ｐｕ在聚变一裂变混合堆内擅变的可行性。选取２３３Ｕ做中子增殖剂，对四个不同燃料组分的快谱包层进行了设计，利用输运一燃耗程序ＢＩＤＥＡＹ对所选方案进行了计算分析，结果表明：用２３３Ｕ做中子增殖剂，在聚变一裂变混合堆快谱包层内擅变２３８Ｐｕ、２４０Ｐｕ、２４２Ｐｕ是安全可行的。     

Determination of Pu isotopes and 241Am in a reference fallout material using SF-ICP-MS

This paper reports on the characterisation of activities of Pu and (241)Am, and Pu isotopic composition in a reference fallout material prepared by the Meteorological Research Institute (MRI), Japan, from samples collected at 14 stations throughout Japan in 1963-1979. The acid leaching and total digestion were used to compare whether there is difference in Pu and (241)Am activities and Pu isotopic composition between these two methods. The results of activities of (239+240)Pu and (241)Pu, and Pu isotopic composition have been reported in the previous work (Sci. Total Environ. 2010, 408, 1139-1144). In this study, the (241)Am activity and (241)Am/(239+240)Pu activity ratio in the reference fallout material are reported, and the usefulness of Pu atom ratios and (241)Am/(239+240)Pu activity ratio for source identification is discussed.     

Ultratrace and isotope analysis of long-lived radionuclides by inductively coupled plasma quadrupole mass spectrometry using a direct injection high efficiency nebulizer

The direct injection high efficiency nebulizer (DIHEN) was explored for the ultrasensitive determination of long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U, (239)Pu, and (241)Am) and for precise isotope analysis by inductively coupled plasma mass spectrometry (ICPMS). The DIHEN was used at low solution uptake rates (1-100 μL/min) without a spray chamber. Optimal sensitivity (e.g., (238)U, 230 MHz/ppm; (230)Th, 190 MHz/ppm; and (239)Pu, 184 MHz/ppm) was achieved at low nebulizer gas flow rates (0.16 L/min), high rf power (1450 W), and low solution uptake rates (100 μL/min). The optimum parameters varied slightly for the two DIHENs tested. The detection limits of long-lived radionuclides in aqueous solutions varied from 0.012 to 0.11 ng/L. The sensitivity of the DIHEN was improved by a factor of 3 to 5 compared with that of a microconcentric nebulizer (MicroMist used with a minicyclonic spray chamber at a solution uptake rate of 85 μL/min) and a factor of 1.5 to 4 compared with that of a conventional nebulizer (cross-flow used with a Scott type spray chamber at a solution uptake rate of 1 mL/min). The precision of the DIHEN ranged from 0.5 to 1.7% RSD (N = 3) for all measurements at the 10 ng/L concentration level (～3 pg sample size). The sensitivity decreased to 10 MHz/ppm at a solution uptake rate of 1 μL/min. The precision was about 5% RSD at a sample size of 30 fg for each long-lived radionuclide by the DIHEN-ICPMS method. The oxide to atom ratios were less than 0.05 (except ThO(+)/Th(+) ) and decreased under the optimum conditions in the following sequence: ThO(+)/Th(+) > UO(+)/U(+) > NpO(+)/Np(+) > PuO(+)/Pu(+) > AmO(+)/Am(+) > RaO(+)/Ra(+). Atomic and oxide ions were used as analyte ions for ultratrace and isotope analyses of long-lived radionuclides in environmental and radioactive waste samples. The analytical methods developed were applied to the determination of long-lived radionuclides and isotope ratio measurements in different radioactive waste and environmental samples using the DIHEN in combination with quadrupole ICPMS. For instance, the (240)Pu/(239)Pu isotope ratio was measured in a radioactive waste sample at a plutonium concentration of 12 ng/L. This demonstrates a main advantage of DIHEN-ICPMS compared with α-spectrometry, which cannot be used to selectively determine (239)Pu and (240)Pu because of similar α energies (5.244 and 5.255 MeV, respectively).     

Transuranium elements in liquid radioactive wastes from the Shelter

The volume activity of ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239+240Pu, ²⁴¹Am, and ²⁴⁴Cm in water taken from unorganized water accumulations on lower marks of the Shelter was determined. Separate water accumulations are characterized by their specific radionuclide activity ratios ²³⁸Pu/^239+240Pu, ²⁴¹Am/^239+240Pu, and ²⁴⁴Cm/²⁴¹Am. The activity ratios ²⁴¹Am/^239+240Pu and ²⁴⁴Cm/^239+240Pu in the water accumulations are 5–10 times higher than in the irradiated fuel of the 4th Unit of the Chernobyl NPP and in lava-like fuel-containing materials.     

An analysis of a puncture wound case with medical intervention

A worker noted a small wound to his thumb when leaving a work site that was undergoing decontamination because of past operations with plutonium (Pu) and americium (Am). Direct surveys of the wound site confirmed the presence of contamination. The chelating agent Ca-DTPA was administered via a nebuliser within an hour after discovery of the wound. External measurements were made of the wound site and wound dressings; 24-h urinary excretion data were collected periodically and the Pu and Am urine content was determined. Zn-DTPA was administered on three occasions. The ICRP Pu systemic model was modified to consider the enhanced urinary excretion following administration of the chelating agents. The analysis indicated that the wound resulted in an initial deposition of 400 Bq 238Pu, 2240 Bq (239/240)Pu and 1060 Bq 241Am. About 70% of the initial wound activity was removed by surgical procedures and less than 1% of the wound activity was removed by chelation therapy. This paper compares the observed urinary excretion data with that indicated by a simulation of the kinetics of the transfer from the wound site and the kinetics of the chelating agent and Pu.     

Individual monitoring of internal exposure at the shelter object

The paper describes how the programme of individual monitoring (IM) of internal exposure (IE) at Shelter object (SO) was designed and what results were obtained in the framework of the programme for 5 y. The main dose-forming factors of IE at SO are intakes of radionuclides of transuranium elements, (90)Sr and (137)Cs. During designing the IM of IE programme, the contribution of each radionuclide was estimated for different types of works and intake paths. The different types of direct and indirect biophysical measurements that could be used for the purposes of IM of IE were analysed. The control of (239+240)Pu content in faecal samples was chosen as a basic type of control of IE. 'Dose per unit content' functions were used for the justification of the IM of IE programme; also, they were used for the assessment of doses of personnel at SO.     

Development of Decay Energy Spectroscopy for Radionuclide Analysis Using Cryogenic 4π Measurements

We report the recent progress in the development of decay energy spectroscopy for radionuclide analysis using a metallic magnetic calorimeter. In the present analysis, sample radionuclides were completely enclosed by a 4π steradian absorber. The use of a 4π absorber composed of gold foil guarantees that the total energy associated with radioactive decay is converted into thermal energy in the absorber. A paramagnetic temperature sensor was attached to the absorber to accurately measure the temperature change due to radioactive decay. The plutonium isotopes ²³⁸Pu, ²³⁹Pu, and ²⁴⁰Pu were readily identified in the decay energy spectrum because each isotope creates a single peak at its characteristic Q value. Two clear peaks were observed for ²³⁹Pu and ²⁴⁰Pu, and a 6.3?keV FWHM was obtained. The energy resolution of the method was affected by the low-energy tail of the spectrum at the left-hand side of the peaks. A 4.1?keV FWHM of a Gaussian fit was obtained for the right-hand side of the peak. Slow heat release to the absorber due to heat flow mechanisms is discussed to explain the low-energy tailing effect.     

Development of a precision spectrophotometric method with internal referencing for determination of metals in nuclear materials: II. Analysis of plutonium in the presence of uranium

Two versions of a spectrophotometric method with internal referencing were developed for determination of the Pu content at U: Pu ratios of 40: 1, 20: 1, and 1: 1. Precision determination of Pu(VI) with a relative root-mean-square deviation (RRMSD) ≤ 0.2% from intrinsic absorption is possible without separation of U with the use of calibration solutions containing U. Under the same conditions, microgram amounts of Pu(IV) in the presence of U (U: Pu = 20: 1) can be determined with an organic reagent, carboxyarsenazo, with RRMSD of 0.3–0.5%. Both versions were successfully applied to analysis of large size dried (LSD) spikes containing 40 mg of U and 2 mg of Pu. All the measurements were carried out on a two-channel spectrophotometric analyzer.     

Using speciated isotope dilution with GC-inductively coupled plasma MS to determine and unravel the artificial formation of monomethylmercury in certified reference sediments

Speciated isotope-dilution mass spectrometry (SID-MS) is claimed to be an absolute method; however, it has been found to be affected by artifact monomethylmercury (MMHg) formation in sediments. The determination of MMHg in sediments was carried out by SID-MS after open-focused microwave extraction. The extracted mercury species were then ethylated and separated by capillary gas chromatography (CGC). Isotope ratios (peak area ratios at different masses) were measured by on-line ICP-MS detection of the CGC-separated compounds. Reproducibility of 202Hg/201Hg isotope ratio measurements were 0.60% for MeEtHg and 0.69% for Et2Hg; for 202Hg/199Hg, 0.43 and 0.46%, respectively, were determined. The absolute detection limits for CGC-ICPMS measurements were better than 26 fg for 202Hg, 20 fg for 201Hg, and 24 fg for 199Hg. For the direct determination of MMHg in sediment reference materials (CRM 580, IAEA 356, and IAEA 405), higher values than the certified were always found. Systematic experiments were carried out to localize the sources of the unintentional abiotic methylmercury formation during analysis. Different spiking and derivatization procedures (either ethylation, propylation, or derivatization by Grignard reagents) were tested. In addition, isotopically enriched inorganic mercury was spiked. The amount of inorganic mercury initially present in the sample was found to be the critical factor that should be known and carefully controlled. A simple solvent extraction technique involving no critical cleanup steps was applied in order to reduce high Hg2+ amounts. The method was applied to the determination of MMHg in sediment reference material IAEA-405 with satisfactory results after organic solvent extraction. The limitations of applicability of the proposed method are evaluated as related to inorganic mercury, organic carbon, and sulfur contents. The results obtained confirmed that available sediment reference materials are adequate to achieve traceable mercury speciation analysis and to detect potential sources of MMHg artifact formation.     

Technical basis for using nose swab bioassay data for early internal dose assessment

One of the challenges to the dose assessment team in response to an inhalation incident in the workplace is to provide the occupational physicians, operational radiation protection personnel and line managers with early estimates of radionuclide intakes so that appropriate consequence management and mitigation can be done. For radionuclides such as Pu, where in vivo counting is not adequately sensitive, other techniques such as the measurement of removable radionuclide from the nasal airway passages can be used. At Los Alamos National Laboratory (LANL), nose swabs of the ET1 region have been used routinely as a first response to airborne Pu releases in the workplace, as well as for other radionuclides. This paper presents the results of analysing over 15 years of nose swab data, comparing these with dose assessments performed using the Bayesian methods developed at LANL. The results provide empirical support for using nose swab data for early dose assessments. For Pu, a rule of thumb is a dose factor of 0.8 mSv Bq(-1), assuming a linear relationship between nasal swab activity and committed effective dose equivalent. However, this value is specific to the methods and models used at LANL, and should not be applied directly without considering possible differences in measurement and calculation methods.     

Soil Contamination with Fuel Component of Chernobyl Radioactive Fallout

Radionuclide activity ratios in the fuel component of the Chernobyl fallout are reestimated on the basis of new experimental data, and maps of the density of contamination of the Chernobyl 30-km zone with ¹⁵⁴Eu, ²³⁸Pu, ^239+240Pu, and ²⁴¹Am as of January 1, 2000 are compiled. The total radionuclide inventories in the top 30-cm horizon of the soil of the 30-km zone (minus the NPP service area, cooling pond, and radioactive waste disposal sites) on January 1, 2000 were estimated to be (Bq): ⁹⁰Sr 7.7×10^{1 4}, ¹³⁷Cs 2.8×10^{1 5}, ¹⁵⁴Eu 1.4 × 10^{1 3}, ²³⁸Pu 7.2 × 10^{1 2}, ^239+240Pu 1.5 × 10^{1 3}, and ²⁴¹Am 1.8 × 10^{1 3}, which makes up to 0.4-0.5% of the total amount of these radionuclides produced in the 4th block of CNPP. This value is lower by a factor of 3 than that generally accepted so far. The radionuclide inventories in other objects of the 30-km zone and beyond it are also estimated. The total amounts of radionuclides fallen out with fuel particles beyond the NPP service area are reestimated. The resulting value (1.5±0.5% of the total produced in the reactor by the accident time) is lower by half as compared to the previous estimates. Two thirds of these amounts are found on the Ukrainian territory.     

Determination of pu isotopes in seawater by an on-line sequential injection technique with sector field inductively coupled plasma mass spectrometry

An on-line sequential injection (SI) system combined with sector field inductively coupled plasma mass spectrometry was developed for the determination of ultratrace level 239Pu and 240Pu in seawater. The potential of this method is the substantial reduction of a sample volume and rapidity in the determination of Pu isotopes. A chemical purification and preconcentration of Pu isotopes were accomplished by the on-line SI system with two microcolumns of solid-phase extraction resins, Sr-Spec and TEVA-Spec. The MCN-6000 microconcentric nebulizer was used as a sample introduction system because of low interference effect and good sample utilization. With this method, it was possible to analyze ultratrace levels of Pu isotopes in only 5 L of surface seawater with an analysis speed of 4 h/sample. The precision of the measurement for the 239Pu and 240Pu was less than 3.4 (n = 7) and 5% (n = 7) for 5 L of seawater. The detection limits for 239Pu and 240Pu were 0.64 (1.5 microBq/mL) and 0.19 fg/mL (1.6 microBq/mL), respectively. The accuracy of this method was verified by using the reference seawater (IAEA-381) as well as by the comparison with the a-spectrometry.     

Assessment of the internal dose of 241Am in bone by in vivo measurements of activity deposited in knee

In case of chronic exposure or long time after an acute intake of (241)Am as a consequence of an incident, the assessment of internal dose might be realised by estimating the total activity content of this element in the skeleton. For this purpose, a new methodology has been developed at the Whole Body Counting Laboratory of CIEMAT. In vivo measurements of this bone-seeker radionuclide in the knee are performed using four low energy germanium detectors inside a shielded room. The sensitivity study of this technique resulted in a minimum detectable activity of 7 Bq, for a counting time of 1800 s. Extrapolation to the total activity in the bone has been carried out by taking into account that the bone content of the knee calibration phantom is equivalent to 10.7% of the whole skeleton mass. The results of in vivo measurements of population and the procedure for internal dose evaluation are presented here.     

USTUR whole body case 0262: 33-y follow-up of PuO2 in a skin wound and associated axillary node

This whole body donation case (USTUR Registrant) involved two suspected PuO2 inhalation intakes, each indicated by a measurable Pu alpha activity in a single urine sample, followed about 1(1/2) y later by a puncture wound to the thumb while working in a Pu glovebox. The study is concerned with modelling simultaneously the biokinetics of deposition and retention in the respiratory tract and at the wound site; and the biokinetics of Pu subsequently transferred to other body organs, until the donor's death. Urine samples taken after the wound incident had readily measurable Pu alpha activity over the next 14 y, before dropping below the minimum detectable excretion rate (<0.4 mBq d(-1)). The Registrant died about 33 y after the wound intake, at the age of 71, from hepatocellular carcinoma with extensive metastases. At autopsy, all major soft tissue organs were harvested for analysis of their 238Pu, 239+240Pu and 241Am content. The amount of 239+240Pu retained at the wound site was 68 +/- 7 Bq (1 SD), measured by low-energy planar Ge spectrometry. A further 56.0 +/- 1.2 Bq was retained in an associated axillary lymph node, measured by radiochemistry. Simultaneous mathematical analysis (modelling) of all in vivo urinary excretion data, together with the measured lung, thoracic lymph node, wound, axillary lymph node and systemic tissue contents at death, yielded estimated intake amounts of 757 and 1504 Bq, respectively, for the first and second inhalation incidents, and 204 Bq for the total wound intake. The inhaled Pu material was highly insoluble, with an estimated long-term absorption rate from the lungs of 2 x 10(-5) d(-1). The Pu material deposited at the wound site was mixed: approximately 14% was rapidly absorbed, approximately 49% was absorbed at the rate of about 6 x 10(-5) d(-1), and the remainder ( approximately 37%) was absorbed extremely slowly (at the rate of about 5 x 10(-6) d(-1)). Thus, it was estimated that only approximately 40% of the Pu initially deposited in the wound had been absorbed systemically over the 33-y period until the donor's death. The biokinetic modelling also indicated that, in this individual case, some of the parameter values (rate constants) incorporated in the ICRP Publication 67 Pu model were up to a factor of 2 different from ICRP's recommended values (for reference man).     

Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour

Subjecting target metallic samples to a very short pulse (about 20 ns) of intense (GW cm⁻²) laser light generates, through a surface plasma, a high-pressure stress wave propagating to the first millimetre in depth, which is commonly called laser shock processing (LSP). The purpose of this work was to evaluate the role of this novel process on the cyclic properties of A356, Al12Si and 7075 aluminium alloys. Major contributors to the fatigue performance improvements were investigated in order to determine the optimum shock conditions. These were mainly compressive residual stress (RS) levels for which a large range of incident shock conditions was performed. We showed that stress levels were very sensitive to the laser fluence and the number of local impacts, and experimental RS measurements were found to be in good agreement with analytical modelling results. In comparison, a conventional shot peening (SP) treatment was found to lead to higher surface hardening and RS levels, but with a very detrimental roughening not observed after LSP. High cycle (10⁷) fatigue tests carried out on laser- processed, shot-peened and untreated notched samples illustrated the efficiency of LSP as a new, promising method to improve the fatigue limits σ_D of structures, especially in comparison with enhancements displayed by SP (+22% vs. +10%). According to crack detection electric measurements, fatigue performance improvements with LSP mainly occurred during the crack initiation stage.     

Determination of 240Pu/239Pu atom ratio in seawaters from the East China Sea

The (240)Pu/(239)Pu atom ratios in seawater samples on the East China Sea continental shelf were measured. These ratios for surface and bottom waters had no significant difference. They were significantly higher than the average global fallout ratio of 0.18. It was proposed that the oceanic currents are accounted for delivery of close-in Pu from the Pacific Proving Grounds (PPG) to the studied areas. The contribution of the PPG close-in fallout was calculated to be 40 % on average. The (240)Pu/(239)Pu atom ratios should provide useful background data before the expected expansion of nuclear power capacity in East and South Asian countries and for distinguishing future sources of Pu.