Comparison of the TriCarb and Hidex 300 SL technique using measurements of (241)Pu and (90)Sr on various samples.

Soil and radioactive slurries were analyzed for the presence of beta emitting (241)Pu and (90)Sr. The comparison study between two different LSC apparatus, TriCarb 2200/2550 and Hidex 300 SL, shows good agreement for the quench corrected (241)Pu activity concentrations. The (90)Sr activity concentrations of most soil samples were in agreement, and were confirmed by the recommended IAEA-375 value. The Hidex 300 SL is an excellent apparatus to measure pure ß-emitters of routine samples.

Determination of (210)Pb and (226)Ra/(228)Ra in continental water using HIDEX 300SL LS-spectrometer with TDCR efficiency tracing and optimized α/ß-discrimination.

An analytical method for determination of (210)Pb, (226)Ra and (228)Ra is presented based on adsorption on 3M Empore RadDiscs, and measurement applying liquid scintillation spectrometry (LSC) after elution. The LSC measurement was performed with optimized α/ß-discrimination and isotope standardization using the triple to double coincidence ratio (TDCR). The consistency of measurement results between radioactive parent-daughter pairs (210)Pb/(210)Bi, (226)Ra/(222)Rn and (228)Ra/(228)Ac was checked in long-term counting experiments and the influence ofinterference of in-growing daughters from (226)Ra into the ß-spectrum of (228)Ra+(228)Ac was studied as well. Recommendations for optimized LSC (228)Ra measurement besides presence of (226)Ra are given.

Determination of 241Pu in nuclear waste slurries: a comparative study using LSC and ICP-MS.

(241)Pu was determined in slurry samples from a nuclear reactor decommissioning project at the Paul Scherrer Institute (Switzerland). To validate the results, the (241)Pu activities of five samples were determined by LSC (TriCarb and Quantulus) and ICP-MS, with each instrument at a different laboratory. In lack of certified reference materials for (241)Pu, the methods were further validated using the (241)Pu information values of two reference sediments (IAEA-300 and IAEA-384). Excellent agreement with the results was found between LSC and ICP-MS in the nuclear waste slurries and the reference sediments.

Separation techniques for low-level determination of actinides in soil samples.

The separation methods for soil samples applied at PSI are based on extraction chromatography and ion exchange. After sample leaching, the actinides are pre-concentrated via precipitation using oxalic acid. Besides the classical separation methods applying the extraction chromatographic resins U/TEVA (for U, Th), TRU (Pu, Am), new methods were recently implemented to increase the radiochemical recovery of particularly trivalent Am and Cm. These methods do not require initial reduction of Pu(IV) to Pu(III) but stabilize Pu on the tetravalent oxidation state using a mixture of NaNO(2)/H(2)O(2) in strong acidic medium. The Pu-fraction is then fixed along with Th onto Dowex AG 1-X2 anion exchanger resin. Th is eluted via complexation with 10M HCl, Pu via reduction with HI. The fractions of Am+Cm and U are loaded onto DGA resin. This resin shows extraordinary high distribution coefficients (k'-values) exceeding 10(4) (for Am) in strong nitric acid medium. The separation between U and Am is obtained quantitatively by decreasing the HNO(3) concentration from 3 to 0.25 M (stripping of the U-fraction) while Am can be easily eluted thereafter using 0.25 M HCl as complexation compound.

Separation of 90Sr from radioactive waste matrices--microwave versus fusion decomposition.

Radioactive waste (slurry) from a detention pond deriving from two research reactors and several inactive and active drain outlets at the Paul Scherrer Institute are the basis for the current (90)Sr investigation. For decomposition, a microwave method was applied, where 1g of dry-ashed slurry was partially dissolved (HNO(3) (65%)/H(2)O(2) (30%); v:v=8:2). In this slurry we obtained an (90)Sr activity of 5.3+/-0.2 Bq/g in solution. In a second run, we applied a borate-fusion (Li metaborate/Li tetraborate (80:20 w/w%) dissolving 1g of dry-ashed "Si-free" slurry at 1100 degrees C in a muffle furnace. We achieved an (90)Sr activity of (7.8+/-0.3)Bq/g, yet observing BaSO(4) precipitation during the chromatographical separation of Sr. An alkali fusion using Na(2)CO(3) was done using the Bunsen burner and the muffle furnace for 20 min at 1000 degrees C, in combination. During formation of the hot glass, the surplus of Na(2)CO(3), produced Na(2)SO(4) and BaCO(3) in solid form. The hot glass was dissolved in deionised water, removing thus the SO(4)(2-) ions. Dissolving the residue directly in HNO(3), solves Ba as Ba(NO(3))(2) and thus we achieved over 80% of the (133)Ba activity in the solution, as measured by gamma-spectrometry. (85)Sr tracer of 88.0%+/-3.3% was recovered, yielding on average in (7.4+/-0.3)Bq/g of (90)Sr activity. The increase of 2.1-2.5 Bq/g of (90)Sr activity achieved with the alkali fusion, and the Li metaborate/Li tetraborate 80:20 w/w% fusion, respectively, clearly shows that some Sr must have been present as SrSO(4) in the slurry.

Radioisotope contaminations from releases of the Tomsk-Seversk nuclear facility (Siberia, Russia).

Soils have been sampled in the vicinity of the Tomsk-Seversk facility (Siberia, Russia) that allows us to measure radioactive contaminations due to atmospheric and aquatic releases. Indeed soils exhibit large inventories of man-made fission products including 137Cs (ranging from 33,000 to 68,500 Bq m(-2)) and actinides such as plutonium (i.e. 239+240Pu from 420 to 5900 Bq m(-2)) or 241Am (160-1220 Bq m(-2)). Among all sampling sites, the bank of the Romashka channel exhibits the highest radioisotope concentrations. At this site, some short half-life gamma emitters were detected as well indicating recent aquatic discharge in the channel. In comparison, soils that underwent atmospheric depositions like peat and forest soils exhibit lower activities of actinides and 137Cs. Soil activities are too high to be related solely to global fallout and thus the source of plutonium must be discharges from the Siberian Chemical Combine (SCC) plant. This is confirmed by plutonium isotopic ratios measured by ICP-MS; the low 241Pu/239Pu and 240Pu/239Pu atomic ratios with respect to global fallout ratio or civil nuclear fuel are consistent with weapons grade signatures. Up to now, the influence of Tomsk-Seversk plutonium discharges was speculated in the Ob River and its estuary. Isotopic data from the present study show that plutonium measured in SCC probably constitutes a significant source of plutonium in the aquatic environment, together with plutonium from global fallout and other contaminated sites including Tomsk, Mayak (Russia) and Semipalatinsk (Republic of Kazakhstan). It is estimated that the proportion of plutonium from SCC source can reach 45% for 239Pu and 60% for 241Pu in the sediments.

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 241Am 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.

A high-resolution abrasive method for determining diffusion profiles of sorbing radionuclides in dense argillaceous rocks.

The diffusion of (134)Cs(+) and (22)Na(+) in Opalinus Clay (OPA) was studied by in-diffusion laboratory experiments. The diffusive tracer profiles in the rock were determined using a high-resolution abrasive peeling method. The radionuclide activities in the grinding swarf were measured directly via gamma-spectrometry. By choosing the appropriate abrasive paper, a resolution down to 15 microm can be achieved. This is important when analysing strongly sorbing radionuclides such as tri- and tetravalent actinides that show steep, shallow diffusion profiles. In this study, a resolution between 20 and 90 microm was obtained which was sufficient for a good spatial resolution of the diffusion profiles. Both the effective diffusion coefficients and the distribution coefficients of the radionuclides could be determined by applying a single reservoir with decreasing source concentration analysis for a semi-infinite case. In the case of (22)Na(+), effective diffusion coefficients of D(e)=2.0 x 10(-11)m(2)s(-1) and D(e)=1.5 x 10(-11)m(2)s(-1) for Benken (Zurcher Weinland) OPA and Mont Terri OPA, respectively, were derived. The distribution coefficients were K(d)=3.1 x 10(-4) and 0.9 x 10(-4)m(3)kg(-1), respectively. For (134)Cs(+) the effective diffusion coefficients were higher, i.e. D(e)=3.1 x 10(-11)m(2)s(-1) for OPA from Benken and D(e)=3.0 x 10(-11)m(2)s(-1) for OPA from Mont Terri. The distribution coefficients determined were K(d)=0.16 m(3)kg(-1) for Benken and 0.23 m(3)kg(-1) for Mont Terri. Comparison of the data obtained for the weakly sorbing (22)Na(+) with those from earlier through-diffusion experiments showed that there is good agreement between the two methods. In the case of (134)Cs(+) such a comparison was not possible because through-diffusion data are not available. Because through-diffusion methods cannot be applied to strongly sorbing tracers in reasonable time periods, in-diffusion combined with high-resolution abrasive peeling offers an excellent alternative for measuring the diffusion properties of strongly sorbing tracers in dense argillaceous rocks.

Fast methods for determination of antropogenic actinides and U/Th-series isotopes in aqueous samples.

Rapid and simple methods are applied at the PSI radioanalytical laboratory for determining anthropogenic actinides in waste and nuclear reactor waters (U, Pu, Am, Cm) as well as for analysis of naturally occurring alpha-emitters in continental river and ground water. Anion exchange chromatography followed by alpha-spectrometry as well as alpha/beta-LSC is applied for the reactor coolant waters. To avoid alpha-spectrum interference between 238Pu and 241Am at 5.5 MeV, the Pu-fraction is purified using anion exchange resin. Prior to the separation of the Pu-fraction, all actinides (U, Pu, Am, Cm) are adsorbed batch-wise under stirring onto Actinide Resin and subsequent decomposition of the reagent. The residue is then re-dissolved in a sulfate buffer solution for electrolytic deposition. In tabular water samples isotopes of Ra and Po are analyzed additionally via sorption onto manganese coated discs (Ra) and deposition on silver discs (Po). For counting times of 1 day and use of 0.1-1l sample aliquots, detection limits of a few mBql(-1) can be obtained easily.

Gross alpha determination in drinking water using a highly specific resin and LSC.

Some results of experiments concerning a new highly specific resin for the extraction of alpha-emitting nuclides from drinking water samples are presented. The product used during these experiments is a new extraction chromatographic resin which consists of a combination of several reagents and extractants supported on inert polymeric substrates, called "Resin" hereafter. It shows strong affinity for Actinides in the tri-, tetra- and hexavalent oxidation state, as well as for radium, even in presence of large amounts of calcium. Gross-alpha activities were determined using alpha-/beta-discrimination liquid scintillation counting (alpha-/beta-LSC) by direct measurement of the dried resin after extraction. Counting conditions were optimised accordingly. A method for the determination of alpha-emitting nuclides in drinking water was developed and tested using intercomparison and spiked drinking water samples.

Incorporation measurements in Switzerland: the approved internal dosimetry service at PSI.

The Swiss radiation protection regulation requires approval of external and internal dosimetry laboratories. The Swiss Personal Dosimetry Ordinance specifies the terms of approval, the survey methods and the standard interpretation to assess the committed effective dose. Specific information is given for 25 radionuclides concerning metabolism, methods of measurement, survey interval and interpretation of the results. On successful completion of a technical audit by an external expert, the dosimetry service of PSI was approved for internal dosimetry by the Swiss authorities by 1 January 2001. The scope of approval includes five different measuring methods for 30 radionuclides.

Determination of 228Ra, 226Ra and 224Ra in natural water via adsorption on MnO2-coated discs.

A fast procedure based on sorption of Ra on MnO2 coated polyamide discs is presented for determination of radium isotopes (i.e. 228Ra, 226Ra, 224Ra) in aqueous samples. The sample discs can be used directly for low-level alpha-spectrometry without the need for further separation and preparation methods to produce planar sample sources. While the activity of alpha-emitting 224Ra and 226Ra can be determined during a first measurement, beta-emitting 228Ra is obtained via ingrowth of the progeny 228Th on the same sample disc after a standing time of about six months. Calculations are presented for optimizing the analytical accuracy as well as for predicting the sorption yield or chemical recovery of radium on the sample disc as a function of exposure time because the sorption uptake proceeds with first-order kinetics. The analyses can be carried out on small samples of 0.5-11 and, for long counting times of one week and use of high-purity silicon surface barrier detectors, a detection limit of 0.15 mBq l-1 is obtained for 226Ra. Since the half-life of 224Ra is only 3.7 d and since 228Th (as a measure for 228Ra) is built up only partially on the sample disc, a slightly higher detection limit of 0.24 mBq l-1 results for the latter isotopes. The procedure is therefore sufficiently sensitive to allow the investigation of Ra isotope relationships in aquifers at typical environmental levels.

228Ra/226Ra/224Ra and 87Sr/86Sr isotope relationships for determining interactions between ground and river water in the upper Rhine valley.

Ground and river waters of the upper Rhine valley (Alsace, France) were investigated for chemical composition of the major elements, Sr isotopes and radionuclides from the U and Th series. In particular, the isotope ratios and concentrations of Ra and Sr were used as geochemical tracers to distinguish between different types of water and their interactions. The bulk chemical analyses suggest that the surface waters in the Rhine valley can be described as mixtures between Ca-Na-HCO3-rich ground water and less mineralized slightly acidic river waters which have migrated through crystalline (mainly granitic) basement rocks of the Vosges mountains. Mixing of these waters yields positive correlation between bulk Sr, U, Ca and HCO3, indicating that carbonate-rich sediments are the main source of U and (non-radiogenic) Sr in the Rhine valley aquifers. The combination of the Ra and Sr isotope systems (228Ra/226Ra, 87Sr/86Sr) shows, however, that probably three sources contribute to the surface river waters in the upper Rhine valley, i.e. (i) a highly radiogenic crystalline component, (ii) a ground water source and, (iii) a third component from infiltrating Rhine water along the flow path of the parallel running river Ill in the northerly direction. The Sr and Ra isotope systems were also used to calculate small-scale mixing fractions of tributaries along the flow path of the Ill. Mixing ratios of non-pure end-member waters were determined using three isotope diagrams (i.e. 224Ra/226Ra vs. 228Ra/226Ra) and the results obtained with the Ra isotope system were found to be consistent with the data using Sr isotope relationships (i.e. 87Sr/86Sr vs. 1/Sr).

Separation and measurement techniques for the determination of 228Th, 230Th and 232Th in various matrices.

Three analytical techniques are presented which are used at PSI for determination of U and Th isotopes (234U, 235U, 238U, 228Th, 230Th, 232Th) in different materials, i.e. environmental samples (soils, minerals) and dental ceramics as well as in urine for in vitro monitoring of potentially exposed workers. Depending on the sample quantity available and/or required detection limits the measurements are performed either directly via gamma spectrometry or via alpha particle counting with preceding separation chemistry. The separation methods applied are based on either extraction chromatography or on sorption of U and Th on actinide selective resin. Following sample digestion, chemical yield spike additions (232U, 225Th or 225Th), chemical purification and electro-depositional source preparation, alpha particle measurement is carried out using low-level alpha spectrometry. This technique allows detection limits of less than 0.2 mBq per counting source if the assay lasts over a few days and is therefore suitable for determination of trace quantities of short-lived 225Th that can be hardly detected by means of mass spectrometric techniques.