Determination of 90Sr, 238Pu, 239,240Pu, 241Pu, and 241Am in soils of chernobyl region using various sample preparation techniques

Radiochemical analysis is made of soddy-podzolic sandy and peaty gley soils collected from the Chernobyl zone. Radionuclides were separated by extraction chromatography or ion exchange, and then determined using an α-ray spectrometer and liquid scintillation and proportional gas counters. Leaching from the preliminarily calcined sample with 8 M HNO₃ does not ensure 100% recovery of radionuclides from peaty gley soil.     

Radiochemical determination of 241Am and Pu(alpha) in environmental materials

Americium-241 and plutonium determinations will become of greater importance over the coming decades as 137Cs and 241Pu decay. The impact of 137Cs on environmental chronology has been great, but its potency is waning as it decays and diffuses. Having 241Am and Pu as unequivocal markers for the 1963 weapon fallout maximum is important for short time scale environmental work, but a fast and reliable procedure is required for their separation. The developed method described here begins by digesting samples using a lithium borate fusion although an aqua regia leachate is also effective in many instances. Isolation of the Am and Pu is then achieved using a combination of extraction chromatography and conventional anion exchange chromatography. The whole procedure has been optimized, validated, and assessed for safety. The straightforwardness of this technique permits the analysis of large numbers of samples and makes 241Am-based techniques for high-resolution sediment accumulation rate studies attractive. In addition, the technique can be employed for the sequential measurement of Pu and Am in environmental surveillance programs, potentially reducing analytical costs and turnround times.     

Twenty-year follow-up of a Pu/Am inhalation case

In 1983 a technician inhaled a mixture of Pu/Am aerosols in an accidental situation in the hotlab of Paul Scherrer Institute (PSI). This case is of interest for long-term follow-up since the technician was relatively young (26 y) at the time of intake, no chelating agent was used to alter retention and excretion and the inhaled activity was rather high ( approximately 20 kBq of alpha emitters). The results obtained from periodic lung counts, urinary and faecal excretions as well as from some bone and liver measurements up to the year 2003 are presented. The measurements were mainly made at PSI but also at FZK Karlsruhe, Germany, and PNNL Hanford, USA. The evaluation and dose estimation of this case was done by several institutions, such as FZK, PNNL and NRPB in addition to PSI. Elements of the case were used in international biokinetic model validation programs by EURADOS/EULEP and IAEA and the (241)Am data are given as example in Annex E of the ICRP 'Guide for the Practical Application of the ICRP Human Respiratory Tract Model'. An overview is given on the various results obtained by the different institutions using their models and methods for interpretation of the measured data. While estimation of intake varies by more than an order of magnitude, final estimation of effective committed dose varies only in the range of 0.5-1.5 Sv.     

Joint determination of 238Pu, 239, 240Pu, 241Pu, and 90Sr in soil

A procedure for determination of ²³⁸Pu, ^{239, 240}Pu, ²⁴¹Pu, and ⁹⁰Sr in soil is reported. ²⁴¹Pu was determined by liquid scintillation counting in the same Pu sample that was obtained from the initial soil sample by coprecipitation with neodymium fluoride and used for α-spectrometric measurements. ⁹⁰Sr was determined by the carbonate method after ion-exchange separation of plutonium. The ⁹⁰Sr activity in the sample was estimated using two measurements of the Cherenkov radiation of ⁹⁰Y, the first made just after separation of ⁹⁰Sr from ⁹⁰Y. This technique allows monitoring of ⁹⁰Y accumulation, excluding contributions from foreign radionuclides. Original Russian Text & V.N. Zabrodskii, Yu.I. Bondar’, A.S. Komarovskaya, V.N. Kalinin, 2006, published in Radiokhimiya, 2006, Vol. 48, No. 1, pp. 87–91.     

Pu and Am Distribution in the System Soil-Water-Carboxylic Resin

Dynamics of Pu and Am distribution between components of the system soil-water-carboxylic resin is studied for soils with various absorbing (clay-humus) complexes. The fractional composition of organic components of the aqueous phase of the system and TUE content in the fractions were examined to elucidate the Pu and Am speciation in the solution. The Pu and Am concentrations in the aqueous phase strongly depend on the content and composition of the soil humus matter. Transuranic elements are associated essentially with the humic acid fractions, this trend being more pronounced for Pu. In the system with increased humus content, TUE occur in the solution as complexes with humus substances, and in the system with lower humus content, as hydrolyzed species. The features of sorption processes occurring on the clayhumus complex of the soil were judged from the sorption isotherms of the radionuclides on a resin. Sorption on the resin is controlled by the Pu and Am speciation in the solution.     

Consequences of 241Am α-decay in some solid matrices

The valence states of “hot” ²³⁷Np atoms arising from α-decay of ²⁴¹Am atoms incorporated in quenched melts of alkali metal nitrates or sorbed on ion-exchange materials were studied by emission Mössbauer spectroscopy.     

Determination of water in NIST reference material for mineral oils

The accuracy of the reference concentrations of moisture in electrical insulating oil RM 8506 and lubricating oil RM 8507 (both of mineral type) and specified by the National Institute of Standards and Technology (NIST) as containing 39.7 and 76.8 ppm (w/w) water, respectively, has recently been the subject of debate in this journal. To shed some further light on this controversy, we report in this correspondence results for these oils obtained by two additional methods, one based on specially designed reagents for diaphragm-free Karl Fischer (KF) coulometry and the other based on the concept of stripping at elevated temperature/continuous KF coulometry. A positive interference effect was shown to take place for RM 8506 when the direct coulometric method was used. If the results are corrected for this, the values including six different procedures varied in the range 13.5-15.6 ppm (w/w). For RM 8507, all values were between 42.5 and 47.2 ppm (w/w), which means that the values recommended by NIST for both reference oils using volumetric titration are about twice as high as those obtained with the other techniques. A possible explanation for this discrepancy is presented.     

241Am as a metabolic tracer for inhaled plutonium nitrate in external chest counting

The plutonium (Pu) treated in the nuclear fuel cycle is usually accompanied by 241Am produced from 241Pu by beta disintegration, which emits gamma rays of 60 keV with the emission rate of 0.36, being more penetrating than the L X rays from Pu. The 241Am could imprve the detection limit of chest counting of Pu, if it was being used as a metabolic tracer for Pu in lungs. Young adult male Wistar rats were exposed to polydisperse aerosols of Pu(NO3)4 with 0.6 microm in activity median aerodynamic diameter. They were periodically killed and the radioactivity of 241Am was cleared from the lungs at almost the same rate as the Pu at least for half a year post-inhalation, which proved the validity of 241Am as a metabolic tracer for inhaled Pu nitrate in external chest counting.     

Study on migration behaviour of 237Np and 241Am in near-surface environments

Laboratory-scale experiments were performed to investigate migration behaviour of (237)Np and (241)Am, which were deposited onto the ground surface from spent fuel reprocessing facilities. Migration experiments by column method were conducted for a sandy soil and a reddish soil by varying the volume of eluting solution. There seemed to be two chemical species of (237)Np in the sandy soil column: one is cationic and the other is particulate form. The particulates moved without significant interaction with the sandy soil. The sorption of cationic (237)Np was controlled by both a reversible ion-exchange reaction and irreversible reactions. Most of (241)Am was formed into rather large particulates and trapped in the sandy soil column. The (237)Np and (241)Am loaded into the reddish soil column moved deeper with increasing eluting volume. The sorption was mainly controlled by ion-exchange reaction. The migration behaviour might be evaluated by the distribution coefficient.     

Chemical resolution of Pu+ from U+ and Am+ using a band-pass reaction cell inductively coupled plasma mass spectrometer

Determination of the concentration and distribution of the Pu and Am isotopes is hindered by the isobaric overlaps between the elements themselves and U, generally requiring time-consuming chemical separation of the elements. A method is described in which chemical resolution of the elemental ions is obtained through ion-molecule reactions in a reaction cell of an ICPMS instrument. The reactions of "natural" U(+), (242)Pu(+), and (243)Am(+) with ethylene, carbon dioxide, and nitric oxide are reported. Since the net sensitivities to the isotopes of an element are similar, chemical resolution is inferred when one isobaric element reacts rapidly with a given gas and the isobar (or in this instance surrogate isotope) is unreactive or slowly reactive. Chemical resolution of the m/z 238 isotopes of U and Pu can be obtained using ethylene as a reaction gas, but little improvement in the resolution of the m/z 239 isobars is obtained. However, high efficiency of reaction of U(+) and UH(+) with CO(2), and nonreaction of Pu(+), allows the sub-ppt determination of (239)Pu, (240)Pu, and (242)Pu (single ppt for (238)Pu) in the presence of 7 orders of magnitude excess U matrix without prior chemical separation. Similarly, oxidation of Pu(+) by NO, and nonreaction of Am(+), permit chemical resolution of the isobars of Pu and Am over 2-3 orders of magnitude relative concentration. The method provides the potential for analysis of the actinides with reduced sample matrix separation.     

Evaluation of committed effective doses from internal contamination of 241Am using experimentally determined parameters of the contaminant

Internal contamination of workers with 241Am has occurred a few times since the beginning of the 1970s, mainly in the workplace where radionuclide sources were produced, and later on, also during liquidation of radioactive waste. Contamination in workers was measured in vivo and bioassay was performed. Solubility of aerosol in lungs was studied by in vitro dissolution test with a simulant solution of the extracellular airway lining fluids. Model calculation for the estimation of intakes was done with the experimentally obtained parameters of aerosol, with modified times of intake, with scattering factors, including Types A and B errors, and with corrections on skull size for in vivo measurements. For most cases, an acceptable fit to the experimental data was obtained; for two cases with intakes taking place long time ago ( approximately 30 y), some changes in the model are necessary.     

Competitive binding of Pu and Am with bone mineral and novel chelating agents

Effective direct removal of actinides such as Pu and Am from bone in vivo has not been accomplished to date, even with the strong chelating agents CaNa3DTPA or ZnNa3DTPA. This study, using an established in vitro system, compared removal of Pu and Am bound to bone mineral by ZnNa3DTPA and 10 chelating agents designed specifically to sequester actinides, including Pu and Am. Ligands tested were tetra, hexa, and octadentate, with linear or branched backbones containing sulfocatechol [CAM(S)], hydroxycatechol [CAM(C)], hydroxipyridinone (1,2-HOPO, Me-3,2-HOPO), or hydroxamate functional groups. The wide range of Pu and Am removal exhibited by the test ligands generally agreed with their metal coordination and chemical properties. The most effective agents for Pu (100 microM concentration, 24-48 h contact) are all octadentate as follows: 3,4,3-LICAM(S) (54% unbound); 3,4,3-LICAM(C) (6.2%); 3,4,3-LI(1,2-HOPO) (3.8%); H(2,2)-(Me-3,2-HOPO) (2.2%) and DFO-(1,2-HOPO) (1.8%). The other ligands removed less than 1% of the bound Pu; and ZnNa3DTPA removed only 0.086%. The most effective ligands for Am removal (100 microM, 24-48 h contact) are as follows: octadentate H(2,2)-(Me-3,2-HOPO) (21% unbound); 3,4,3-LI(1,2-HOPO) (14.5%) and 3,4,3-LICAM(C) (5.9%); hexadentate TREN-(Me-3,2-HOPO) and TREN-(1,2-HOPO) (9.6%); and tetradentate 5-LIO(Me-3,2-HOPO) (5.2%). Am removal by ZnNa3DTPA was about 1.4%. Among the ligands presently considered for possible human use, only 3,4,3-LI(1,2-HOPO) removed potentially useful amounts of both Pu and Am from bone mineral.     

Characterisation of a setup for mixed beam exposures of cells to 241Am alpha particles and X-rays

Exposure of humans to mixed fields of high- and low-linear energy transfer (LET) radiation occurs in many situations-for example, in urban areas with high levels of indoor radon as well as background gamma radiation, during airplane flights or certain forms of radiation therapy. From the perspective of health risk associated with exposure to mixed fields, it is important to understand the interactions between different radiation types. In most cellular investigations on mixed beams, two types of irradiations have been applied sequentially. Simultaneous irradiation is the desirable scenario but requires a dedicated irradiation facility. The authors have constructed a facility where cells can be simultaneously exposed to (241)Am alpha particles and 190-kV X-rays at 37°C. This study presents the technical details and the dosimetry of the setup, as well as validates the performance of the setup for clonogenic survival in AA8 Chinese hamster ovary cells. No significant synergistic effect was observed. The relative biological effectiveness of the alpha particles was 2.56 for 37 % and 1.90 for 10 % clonogenic survival.     

The choice of gamma spectrometer for determining the content of 241Am

An express-estimation algorithm for determining the minimum detectable activity of ²⁴¹Am is developed. Semiconductor spectrometers manufactured by the ORTEC Company (USA) and scintillation spectrometers manufactured by the Atomtekh Company (Belarus) are compared. It is proposed to use the results to estimate the suitability of the existing inventory of measuring instruments for the radiation monitoring of territory contaminated by ²⁴¹Am. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 62–66, September, 2006.     

A specific voxel phantom for in vivo measurements of 241Am in the knee

Calibration phantoms for in vivo measurements of low-energy photons should be anatomically realistic to minimise the uncertainties in the activity assessment. The calibration of the detection system can be performed using computational techniques based on numerical phantoms. The purpose of this work is to approach a numerical calibration by Monte Carlo (MC) technique of a Germanium detection system for the determination of 241Am in the knee. A specific voxel phantom was built from a computerised tomography of the calibration Spitz knee phantom. The phantom and the procedure to generate the associated input file for the MC code, namely MCNPX, have been described, as well as the characterisation of the detectors according to the manufacturer data and the energy calibration curves of the spectrometer. The detection efficiency and the pulse-height distribution have been determined for a homogeneous contamination of 241Am in bone.     

Association of 90xSr, 137Cs, 239,240Pu, 241Am,and 244Cm with Soil Absorbing Complex in Soils Typical of the Vicinity of the Chernobyl NPP

Association of the main long-lived radionuclides ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm with various components of the soil absorbing complexes from soil samples collected along the western, northwestern, and northern tracks of radioactive fallout in the vicinity of the Chernobyl NPP was studied by the sequential leaching. In the samples of the sandy soil collected in the floodplain of the Pripyat river along the northwestern radioactive track, more than 85% of ⁹⁰Sr, 55% of ^239,240Pu, and 75% of ²⁴¹Am and ²⁴⁴Cm are associated with various components of the soil absorbing complex and are potentially mobile species. In the soil samples collected along the narrow western track, 80-85% of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm are incorporated in hot particles. The degree of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²⁴¹Am, and ²⁴⁴Cm association with different components of the soil absorbing complex is a function of the radionuclide type and physicochemical features of soil.     

Effect of Contact Time of Liquid Radioactive Waste with Bed Rock of Underground Repository on Migration Behavior of 90Sr, 137Cs, 239Pu,and 241Am

Behavior of radionuclides caused by interaction of acidic waste with sandy bedrock in deep underground repositories is studied, including sorption-desorption of ⁹⁰Sr, ¹³⁷Cs, ²³⁹Pu, and ²⁴¹Am. The amount of mobile forms of radionuclides decreases with increasing contact time with bedrock, thus decreasing the migration rate of the radionuclides in the collector bed.