Fast method for the determination of radiostrontium and plutonium isotopes in food samples

Rapid radioanalytical methods are important in the case of a radiological emergency and for the defence against nuclear hazards, especially for pure alpha and beta emitters like ^239/240Pu and ⁸⁹Sr/⁹⁰Sr. A new fast method was developed with an overall analysis time altogether around 11 h, for only strontium isotopes about 7 h. The method combines two extraction chromatography resins, DGA- and Sr-resin, to separate mainly strontium and plutonium. A broad variety of food samples with different fat, carbohydrate and protein contents were tested and successfully analysed. The yields obtained were typically around 95% and 70% for ⁹⁰Sr and ²⁴²Pu.

     

Determination of137Cs,90Sr and fallout Pu in the volcanic soil of Korea

The cumulative depositions of¹³⁷Cs,⁹⁰Sr and fallout Pu in the volcanic ash soil of Korea were determined. The average accumulated depositions of¹³⁷Cs,⁹⁰Sr and fallout Pu in the volcanic soil were much higher than those in other forest sites of Korea. From depth profiles, it was found that¹³⁷Cs,⁹⁰Sr and^239,240Pu in the volcanic soil are more mobile than those in other forest sites of Korea, and that the downward movement of⁹⁰Sr is faster than¹³⁷Cs and^239,240Pu. A significant correlation was found between the concentration of¹³⁷Cs and those of⁹⁰Sr and^239,240Pu. The activity ratios of²³⁸Pu/^239,240Pu and²⁴¹Pu/^239,240Pu in soils are close to those observed in the cumulative deposit from the global fallout of nuclear weapon testings.     

Analytical Methods for the Determination of 90Sr and 239,240Pu in Environmental Samples

Artificial long-lived radionuclides such as ⁹⁰Sr and ^239,240Pu have been long released into the environment by human nuclear activities, which have a profound impact on the ecological environment. It is of great significance to monitor the concentration of these radionuclides for environmental safety. This paper summarizes and critically discusses the separation and measurement methods for ultra-trace determination of ⁹⁰Sr, ²³⁹Pu, and ²⁴⁰Pu in the environment. After selecting the measurement method, it is necessary to consider the decontamination of the interference from matrix elements and the key elements, and this involves the choice of the separation method. Measurement methods include both radiometric methods and non-radiometric methods. Radiometric methods, including alpha spectroscopy, liquid scintillation spectrometry, etc., are commonly used methods for measuring ^239+240Pu and ⁹⁰Sr. Mass spectrometry, as the representative of non-radiometric measurement methods, has been regarded as the most promising analytical method due to its high absolute sensitivity, low detection limit, and relatively short sample-analysis time. Through the comparison of various measurement methods, the future development trend of radionuclide measurement is prospected in this review. The fully automatic and rapid analysis method is a highlight. The new mass spectrometer with ultra-high sensitivity shows strong analytical capabilities for extremely low concentrations of ⁹⁰Sr, ²³⁹Pu, and ²⁴⁰Pu, and it is expected to develop determination methods with higher sensitivity and lower detection limit.     

Deposition of90Sr and plutonium isotopes derived from the Chernobyl accident in Japan

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (^239,240Pu,²³⁸Pu,²⁴¹Pu and⁹⁰Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of⁹⁰Sr differed from that of volatile radionuclides such as¹³¹I and¹³⁷Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of⁹⁰Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher²⁴¹Pu deposition in most of the stations, as well as high²³⁸Pu/^239,240Pu activity ratios were observed. The²⁴¹Pu/²³⁸Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than¹³⁷Cs.     

Scaling model for prediction of radionuclide activity in contaminated soils using a regression triplet technique

A scaling model was built to calculate the activity of alpha emitting radionuclides in contaminated soil in the lysimeter field. Linear regression can be applied for the evaluation of radioactivity measurement data. Activities of the radionuclides ²⁴¹Am, ²³⁸Pu, ^239,240Pu and ⁹⁰Sr obtained by experiments from real contaminated soils of the experimental lysimeter placed in a nuclear power plant (NPP) in Slovakia were evaluated using linear regression models with the method of least squares. A suitable scaling model for monitoring the ²⁴¹Am, ²³⁸Pu, ^239,240Pu alpha radionuclide activity was built using the regression triplet analysis and regression diagnostics. A regular designed scaling model opens the possibilities of longtime activity monitoring of these radionuclides, thus decreasing the number of necessary radiochemical analyses. The Fisher-Snedecor test, however, confirmed that the regression model for ⁹⁰Sr activity monitoring by ²⁴¹Am, ^239,240Pu activity determination in contaminated soils can not be recommended.     

Retrospective determination of 238Pu, 239,240Pu and 90Sr activities in the outer bark of Norway spruce (Picea abies (L.) Karst.) collected at various sites in the Czech Republic

The activity concentrations of ²³⁸Pu, ^239,240Pu and ⁹⁰Sr were determined in 25 archived spruce outer bark samples collected in coniferous forests across the Czech Republic in 1995. At three sampling sites the radionuclide activity concentrations were determined in forest soil. Data was provided on the cumulative deposition and vertical distribution of ²³⁸Pu, ^239,240Pu and ⁹⁰Sr in forest soil. The median activity concentration of ²³⁸Pu in the spruce bark samples was 0.009 Bq kg^?1. The median activity concentration of ^239,240Pu was 0.212 Bq kg^?1, and the median activity concentration of ⁹⁰Sr was 10.6 Bq kg^?1. The radionuclide activity concentration distribution was not significantly explained by the local long-term (1961–2000) mean annual precipitation totals, by site elevation, by bark acidity, by soil moisture and soil texture. The activity concentrations of the radionuclides in bark were found to be higher than or comparable with the published and measured figures for radionuclide activity concentrations in cultivated and uncultivated soils (0–20 cm layer) in the Czech Republic and abroad. The activity concentration ratio of ⁹⁰Sr/^239,240Pu in the investigated spruce bark samples was higher than in the relevant soil samples. We assume that the crucial radioactive contamination loads in bark occurred in the first half of the 1960s, when the concentration of the investigated radionuclides in the air was highest. Spruce trunk bark has preserved relatively high activity concentrations of these radionuclides. The mechanism governing the long-term radionuclide activity concentrations in outer bark proportional to the local radioactive fallout rates is not correctly known. Our results indicate the suitability of spruce bark for use as an effective monitor of radioactive plume fallout loads even several decades after the contamination episode.     

Rapid determination of 239,240Pu, 238Pu, 241Am and 90Sr in radioactive waste using combined SPE sorbents AnaLig? Pu02, AnaLig? Sr01 and TRU? Resin

A rapid separation method has been developed which allows measurement of plutonium, americium and strontium isotopes in the radioactive sludge from Nuclear power plant A1 Jaslovske Bohunice (NPP A1) with high chemical recoveries and effective removal of matrix interferences. This method uses different commercial products stacked AnaLig^? Pu02, AnaLig^? Sr01 and TRU^? Resin cartridges from IBC Advanced Technologies and Eichrom Technologies. The method allows the rapid separation of plutonium, strontium and americium using a single multi-stage column in the vacuum box (cartridge technology) with rapid flow rates to minimize sample separation time. The ^239,240Pu, ²³⁸Pu and ²⁴¹Am were determined by alpha spectroscopy, ⁹⁰Sr was counted on TRICARB 2900 TR by Cerenkov counting of its progeny ⁹⁰Y.     

Study of 137Cs, 90Sr, 239,240Pu, 238Pu and 241Am behavior in the Chernobyl soil

The vertical distribution of ¹³⁷Cs, ⁹⁰Sr, ^239,240Pu, ²³⁸Pu and ²⁴¹Am was determined in soil samples collected from the Chernobyl exclusion zone in 1994. The results show very close distribution profiles for all radionuclides, with about 90% of the total activity of each nuclide lying between the surface and the fourth centimeter. Sequential extraction methods were used to determine the association of radionuclides in soil. The data on vertical distribution of radionuclide species were used to calculate their vertical migration parameters.     

Artificial radioactive contamination of sediments along the Romanian sector of the Danube river and the Black Sea coast

The concentrations of⁹⁰Sr,²³⁸Pu,^239,240Pu and²⁴¹Am were determined in 12 sediment samples, collected from the bed of the Romanian sector of the Danube river and the Black Sea coast during 1996–1997. The samples were dissolved using a microwave digestion technique which left the refractory part of the samples undissolved. Part of the samples were also dissolved totally by alkaline fusion. The results obtained after radiochemical separations and measurement of the radionuclides by the two dissolution methods were compared recommending the optimum method. The radioactive contamination of the investigated sector in 1996–1997 is compared with the results obtained for the same locations in 1994–1995 reported in previous papers.     

The IAEA Proficiency Test on Evaluation of Methods for 90Sr Measurement in a Mineral Matrix; Preliminary Evaluation of Sources of Bias and Measurement Uncertainties

The results from numerous intercomparison exercises and proficiency tests indicate that the measurement of ⁹⁰Sr in solid environmental matrices poses a problem to many analysts. The causes of the observed scatter of analytical results are not well understood and therefore difficult to remedy. In order to assess the effect of various analytical operations and measurement routines on the quality of the ⁹⁰Sr data, the IAEA's Analytical Control Services have organised a proficiency test using a mineral sample spiked at three different levels with known amounts of ⁹⁰Sr. This proficiency test generated considerable interest from the radioanalytical community as a total of 192 sets of samples were distributed to 158 radioanalytical laboratories world-wide. The reported data were evaluated with respect to their relative bias against the reference value and with respect to their reported overall uncertainty. The major sources of bias leading to overestimated values are ineffective purification procedures, high background values and a lack of statistical control over background values. The major sources of bias leading to an underestimation are overestimated recovery factors in part due to failure to correct for stable Sr in the sample and possibly failure to correct for quenching in liquid scintillation counting. Preliminary results for a small randomly selected group of laboratories are presented.     

Geochemical studies on the Chernobyl radioactivity in environmental samples

Artificial radionuclides in deposition and airborne dust samples in 1986 were measured at Tsukuba and 11 stations in Japan. In May 1986, the Chernobyl radioactivity was observed in rain and air samples in Japan. The Chernobyl-derived Pu isotopes, which are characterized by higher²³⁸Pu/^239,240Pu (85) and²⁴¹Pu/²³⁸Pu (0.5) activity ratios than those of the nuclear test-derived Pu and⁹⁰Sr, were detected in deposition and airborne dust samples in Japan, as well as volatile radionuclides such as¹³¹I and¹³⁷Cs. However, the activities of Pu isotopes and⁹⁰Sr observed in Japan were about two and three orders of magnitude lower than those expected from the activity ratios in the total release at Chernobyl, which means that the residence time of Pu in the air was shorter than that of¹³⁷Cs. In order to understand the fractionation between the Chernobyl radionuclides we studied about individual wet and dry deposition. The results suggest that this cause is due to the difference of the particle size of radionuclide-bearing particles, which may be related to the release process of Chernobyl radionuclides.     

The NIST natural-matrix radionuclide standard reference material program for ocean studies

In 1977, the Low-level Working Group of the International Committee on Radionuclide Metrology met in Boston, MA (USA) to define the characteristics of a new set of environmental radioactivity reference materials. These reference materials were to provide the radiochemist with the same analytical challenges faced when assaying environmental samples. It was decided that radionuclide bearing natural materials should be collected from sites where there had been sufficient time for natural processes to redistribute the various chemically different species of the radionuclides. Over the succeeding years, the National Institute of Standards and Technology (NIST), in cooperation with other highly experienced laboratories, certified and issued a number of these as low-level radioactivity Standard Reference Materials (SRMs) for fission and activation product and actinide concentrations. The experience of certifying these SRMs has given NIST the opportunity to compare radioanalytical methods and learn of their limitations. NIST convened an international workshop in 1994 to define the natural-matrix radionuclide SRM needs for ocean studies. The highest priorities proposed at the workshop were for sediment, shellfish, seaweed, fish flesh and water matrix SRMs certified for mBq per sample concentrations of ⁹⁰ Sr, ¹³⁷ Cs and ²³⁹ Pu + ²⁴⁰ Pu. The most recent low-level environmental radionuclide SRM issued by NIST, Ocean Sediment (SRM 4357) has certified and uncertified values for the following 22 radionuclides: ⁴⁰ K, ⁹⁰ Sr, ¹²⁹ I, ¹³⁷ Cs, ¹⁵⁵ Eu, ²¹⁰ Pb, ²¹⁰ Po, ²¹² Pb, ²¹⁴ Bi, ²²⁶ Ra, ²²⁸ Ra, ²²⁸ Th, ²³⁰ Th, ²³² Th, ²³⁴ U, ²³⁵ U, ²³⁷ Np, ²³⁸ U, ²³⁸ Pu, ²³⁹ Pu + ²⁴⁰ Pu, and ²⁴¹ Am. The uncertainties for a number of the certified radionuclides are non-symmetrical and relatively large because of the non-normal distribution of reported values. NIST is continuing its efforts to provide the ocean studies community with additional natural matrix radionuclide SRMs. The freeze-dried shellfish flesh matrix has been prepared and recently sent to participating laboratories for analysis and we anticipate receiving radioanalytical results in 2000. The research and development work at NIST produce well characterized SRMs that provide the world's environment-studies community with an important foundation component for radionuclide metrology.     

Depth profiles of long lived radionuclides in Chernobyl soils sampled around 10 years after the accident

Depth profiles of the long-lived radionuclides, ¹³⁷Cs, ⁹⁰Sr, Pu isotopes and ²⁴¹Am were examined in undisturbed sandy, peaty and Podsol soils in the Chernobyl 30 km exclusion zone sampled around 10 years after the accident. Two Podsol soils, which have different radioactive deposition characteristics, have also been examined. Activity ratios of ^239,240Pu/¹³⁷Cs, ⁹⁰Sr/¹³⁷Cs, and ²⁴¹Am/¹³⁷Cs in the 0-1 cm layer of the two Podsol soils differed very much. Speciation of the radionuclides by sequential selective extraction was examined in the soils. Depth profiles of the soils have been analyzed according to the speciation results and soil characteristics.     

Artificial radioactive contamination of sediment samples along the Romanian sector of the Danube river and the Black Sea coast

The concentrations of¹³⁷Cs were determined by in 11 sediment samples, collected along the Romanian sector of the Danube river and the Black Sea coast during 1994 γ-ray spectrometry. The concentrations of⁹⁰Sr in the same sediment samples were determined by β-counting of the⁹⁰Y oxalate, precipitated after strontium separation using a strontium extraction chromatography column. The concentration distributions of¹³⁷Cs and⁹⁰Sr are compared with the²³⁸Pu and^239,240Pu concentration distributions in the same samples, reported in a previous paper. The accumulation potential of¹³⁷Cs,⁹⁰Sr and plutonium isotopes in the river and sea sediments analysed is discussed.     

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.     

Adaptation of a radioanalytical method for strontium-90 to different kinds of environmental samples and its application for the investigation of some samples in the Riyadh region

A relatively simple and rapid radioanalytical method, limited to milk, is adapted for investigating soil, biological and water samples for⁹⁰Sr. The method is based on a selective separation and successive counting of equilibrium quantities of its daughter 90Y, which can be extracted by tributyl phosphate from nitrate medium and stripped by conc. ammonia solution. 90Y is separated from possible iron and measured by Cerenkov counting. The procedure is thoroughly tested with certified reference materials and used lately for determining⁹⁰Sr in some environmental samples in the Riyadh region. The results obtained are given and discussed.     

Monitoring the environmental contamination of Kara Sea and shallow bays of Novaya Zemlya

The distribution of ¹³⁷Cs and ^239,240Pu in various ecosystems of the Kara Sea as well as speciation of these radionuclides has been studied to assess their potential mobility. In bottom sediment and seawater samples collected in Abrosimov, Tsivolky, Stepovoy, and Sedov Bays and on the coast of Novaya Zemlya, the content of anthropogenic radionuclides ¹³⁷Cs and ^239,240Pu does not exceed the values typical of the offshore zone in the Kara Sea (in sea water: 1.0–3.7 Bq/m³ for ¹³⁷Cs and 50–90 mBq/m³ for ^239,240Pu; in bottom sediments: 0.5–18.3 Bq/kg for ¹³⁷Cs and 4.3–7.3 Bq/kg for ^239,240Pu). The present monitoring study is important for the development of a long-term forecast for the dynamics of environmental contamination in the shallow bays of Novaya Zemlya.     

Enzymatic degradation of large vegetation samples for the simultaneous determination of129I,actinides and strontium

A radiochemical procedure is given for the simultaneous determination of low levels of¹²⁹I, actinides (Pu, Am, Cm) and⁹⁰Sr in vegetation samples. It is shown that grass samples up to 5 kg fresh weight can be wet ashed conveniently by hydrogen peroxide under alkaline conditions, subsequent to an initial enzymatic disintegration. After purification of the iodine fraction,¹²⁹I is determined by neutron activation analysis. Using alpha spectrometry,²³⁸Pu and^239,240Pu are determined in the plutonium fraction, and²⁴¹Am,²⁴²Cm, and²⁴⁴Cm in the americium/curium fraction. The⁹⁰Sr is determined after separation by beta counting its decay product⁹⁰Y.     

Rapid determination of 239,240Pu, 238Pu, 241Am and 90Sr in high contaminated samples waste using combined SPE sorbents AnaLig® Pu-02, AnaLig® Sr-01 and DGA® Resin

A rapid separation method has been developed which allows measurement of plutonium, americium and strontium isotopes in the high active sample from CBRN Training and Testing Centre in Zemianske Kostolany (Slovakia) with high chemical recoveries and effective removal of matrix interferences. This method uses different commercial products stacked AnaLig^® Pu-02, AnaLig^® Sr-01 and DGA^® Resin cartridges from IBC Advanced Technologies and Eichrom Technologies. The method allows rapid separation of plutonium, strontium and americium using a single multi-stage column in the vacuum box (cartridge technology) with rapid flow rates to minimize sample separation time. The ^239,240Pu, ²³⁸Pu and ²⁴¹Am were determined by alpha spectroscopy, ⁹⁰Sr was counted on TRICARB 2900 TR by Cerenkov counting of its progeny ⁹⁰Y.     

Certified reference material for radionuclides in seawater IAEA-381 (Irish Sea Water)

A certified reference material (CRM) for radionuclides in seawater, IAEA-381 (Irish Sea Water), is described and the results of certification are presented. The material has been certified for nine radionuclides (⁴⁰K, ⁹⁰Sr, ¹³⁷Cs, ²³⁷Np, ²³⁸Pu, ²³⁹Pu,²⁴⁰Pu, ^239,240Pu and ²⁴¹Am). Information on massic activities with the corresponding 95% confidence intervals are given for eight radionuclides (³H, ¹²⁵Sb, ²³⁴U, ²³⁵U, ²³⁶U, ²³⁸U, ²⁴¹Pu and ²⁴⁴Cm). Less reported radionuclides include ⁶⁰Co, ⁹⁹Tc, and ²⁴²Pu. The CRM may be used for quality assurance/quality control of the analysis of radionuclides in environmental water samples, for the development and validation of analytical methods and for training purposes. The material is available from the IAEA in 5 kg units.