Yield Tracer Research Articles

Envirogeochemical exploration for "NORM" wastes: quadrupole inductively coupled plasma mass spectrometric measurements of thorium and uranium isotopes

Naturally occurring radioactive material consists of 238U, 235U and 232Th and series daughters; it is released into the environment from many anthropogenic sources. The use of quadrupole ICP-MS is well-suited to site investigations of releases of naturally occurring radioactive material through measurements of the ratios 232Th∶230Th, 230Th∶238U and 234U∶238U. Each ratio measurement may potentially indicate the contrast between the geochemical background and the affected environment. 232Th∶230Th was measured in samples prepared by fusion or selective extraction; Th was concentrated using TRU-Spec extraction resin and isotopic measurements were made with 5–10 µg Th. The precision is ≈1% (2σmean) and 10% for 232Th∶230Th of 1 000 and 100 000–200 000, respectively. Thorium isotopic measurements were applied to studies of accumulation of 230Th in phosphate-fertilized lawns. The ratio 230Th∶238U was determined via combining separate measurements of 230Th∶232Th and 232Th∶235U or 232Th∶238U; a 230Th∶238U precision of 1–2% (2σmean) is reported for a phosphate fertilizer sample. This 230Th∶238U measurement scheme requires no synthetic yield tracers, and is applied to studies of deposition of U mill tailings in an affected river basin. The ratio 234U∶238U was determined in natural waters following a two-stage extraction with Chelex 20 and UTEVA resins; a precision of ≈0.3–0.5% (2σmean) is attained for sample concentrates containing 15–25 µg U. 234U∶238U measurements are useful in distinguishing between dissolved U from natural weathering versus mining/milling sources.

Determination of polonium-210 in phosphoric acid

Polonium-210 in phosphoric acid has been recognized as a significant source of alpha contamination of processed Si-wafers for memory devices of computer. In the present work, a convenient method was developed for the determination of trace210Po in phosphoric acid of high purity. For the determination,209Po was used as a yield tracer. The present method consists of (1) addition of the tracer to 5 ml aliquot of phosphoric acid sample, (2) pH adjustment (to 2) of the sample solution to make up electrolytic solution, (3) electrodeposition for the simultaneous achievement of Po separation and preparation of counting source on stainless-steel disc, and (4) alpha-ray spectrometry. By the developed method, more than 95% of Po was separated from phosphoric acid sample onto counting disc. The minimum detectable radioactivity of210Po in 5 ml of phosphoric acid was about 0.03 mBq by counting the electrodeposited alpha-activity for 10 days under a counting efficiency of ≈30%.

A dual radiotracer speciation technique with emphasis on probing of artefacts: a case study for technetium and spinach ( Spinacia oleracea L.)

Speciation is required for obtaining information on chemical reactivity, toxicity and bioavailability of an element. In this work, a novel analytical speciation methodology, using a dual radiotracer technique is described. The approach is illustrated with the speciation of 99 Tc , a pure β −-emitter, in spinach plants. The actual leaf concentration of two technetium species, i.e. 99 TcO − 4 and 99 TcX (plant-formed Tc species), is determined as a function of incubation time with 99 TcO − 4 in the substrate. Addition of 95 m TcO − 4 or 99 m TcO − 4 , both containing a γ-emitting radioisotope of technetium, to the substrate allows easy radiotracing, while addition of 99 m TcO − 4 or 95 m TcX yield tracers during the analytical homogenisation procedure makes it possible to correct for procedural losses and redox conversions. For TcO − 4 significant procedural losses were observed, while for TcX procedural recovery was nearly quantitative. Significant procedural conversions of TcO − 4 or TcX were not observed. Speciation of other elements might benefit from this novel methodology.

Vertical profiles of 239,240Pu and 241Am in two sphagnum mosses of Italian peat

During the last two years the Urbino University and the Padua ICTIMA CNR collaborated on a special radioecological program having the aim to study the Pu and Am retention behaviour in Sphagnum peat in the Alps region (northern Italy). 239,240Pu, 238Pu and 241Am were separated and determined by extraction chromatography, electroplating and alpha spectrometry; 242Pu and 243Am were used as the yield tracers. The paper summarizes the results dealing with the vertical profiles of the radionuclides in Sphagnum compactum and S. nemoreum. Several 1–2 cm high sections were obtained and dated by 210Pb determination. Typical concentration peaks for Pu and Am were found at a depth corresponding to the early 1960s which is the period characterized by the maximum nuclear weapon tests.

Pulse time interval analysis (TIA) combined with liquid scintillation counting for the determination of environmental α-nuclides: Preparation and utilization of225Ra as a yield tracer

Time interval analysis (TIA), which has been verified to be suitable for the selective extraction of correlated successive α-decay events within a liquid scintillator, was further developed by combining pulse shape discrimination technique and simple chemical analysis. A β-emitter nuclide,225Ra, which is suitable for the use as a yield tracer belonging to Np-decay series, was also found to be detectable by the TIA-method after a certain standing period when the radium-extractant (RADAEX) was added small amounts of HDEHP [di (2-ethylhexyl) phosphoric acid], which was proved to keep the equilibrium state between Ra and its descendants. The present counting system (TIA analysis incorporated α-LSC/PSD) has been verified to be applicable to the simultaneous determination of three (including Th, Ac, and Np) decay series, if the chemical purification of radium fraction was applied to the environmental samples using an extractive scintillator in addition to utilization of an α-peak itself at lowest energy for the determination of226Ra in uranium decay series. This radioanalytical method was practically applied to the determination of natural radionuclides belonging to three decay series in environmental samples and compared to the alpha-spectrometric results using a Si-surface barrier detector (SSB).

A fast method for the simultaneous determination of 230Th, 234U and 235U with isotope dilution sector field ICP-MS

A double focussing sector field ICP-MS with its variable resolution capability was used for the simultaneous measurement of Th and U isotopes to calculate excess 230Th and total U content in marine sediments. The necessary separation and concentration of Th and U from major and minor elements in the sediment samples was achieved by acid digestion followed by anion exchange. ICP-MS measurements were performed using a resolution of R = 4430 resulting in an abundance sensitivity of 230/232 = 5 × 10–7 which is small enough for the quantification of sediments with 230Th/232Th ratios as low as 10–6. Using a microconcentric nebulizer (MCN-100), the lowest sample volume required for a single measurement was less than 200 µl. Analysis time was 80 s per sample. 229Th and 236U were used for quantification and as yield tracers. The overall uncertainty introduced by the entire separation procedure and the ICP-MS analyses was about 5% (95% confidence interval). The precision of each individual measurement was within 3% (2s).

Concentration and speciation of plutonium, americium, uranium, thorium, potassium and 137Cs in a venice canal sediment sample

A sequential extraction method consisting of six operationally-defined fractions has been developed for determining the geochemical partitioning of natural (U, Th, 40K) and antropogenic (Pu, Am, 137Cs) radionuclides in a 40–50 cm deep sediment sample collected in a Venice canal. Extraction chromatography with Microthene-TOPO (U, Th), Microthene-TNOA (Pu) and Microthene-HDEHP (Am) column was used for the chemical separation of a single radionuclide; the final recoveries were calculated by adding 236U, 229Th, 242Pu and 243Am as the yield tracers. After electrodeposition the alpha spectrometry was carried out. 137Cs and 40K were measured by gamma spectrometry. The total concentrations in the wet sample (Bq/kgd), obtained by a complete disgregation of the matrix by wet and dry treatment, were the following: 239+240Pu=1.03±0.07, 238Pu=0.022±0.005, 241Am=0.337±0.027, 137Cs=9.78±0.78, 238U=28.84±1.62, 232Th=21.42±1.93, 40K=376.05±12.78. The mean ratio 238Pu/239+240Pu (0.02) shows a contamination due essentially to fall-out and U and Th alpha spectra indicate the natural origin of two elements. The absence of 134Cs in the sample proves that at 40–50 cm depth the sediment was not affected by the Chernobyl fall-out. As far as the speciation is concerned the following fractions were considered: water soluble, carbonates, Fe−Mn oxides, organic matter, acid soluble, residue. Pu (∼67%) an Am (∼95%) were present principally in the carbonate fraction; U was more distributed and about 30% and 45% appeared in the carbonate fraction and in the residue respectively; the majority of Th was present in the residue (∼60%); 40K was totally present in the residue; finally 137Cs was found mostly in the acid soluble fraction (∼53%) and in the residue (∼47%). Some stable elements (Fe, Mn, Al, Ti, Ca, Pb, Ba) were also determined in the different fractions to get more information about the chemical association of the single radionuclides.

Fast source preparation for alpha-spectrometry of uranium and transuranium isotopes

A very fast and simple source preparation procedure for α-spectrometry, especially for the Large-Area Grid Ionization Chamber, has been developed. It is based on two liquid-liquid extractions and direct evaporation of the extractants, containing the uranium and transuranium isotopes, on the counting dishes. From the sample two thin-layer counting sources are prepared to take into account the α-spectrometric interference of the nuclides234U−237Np and238Pu−241Am, where one counting source contains the U- and Pu-isotopes and the other one the Np- and Am-isotopes. The chemical yields are in the range of 95 and 98% so that no yield tracers are necessary. Starting with the dissolved sample, the two counting sources can be prepared in only about 1 hour. A second even faster preparation version, with only one counting source, has been devised, if discrimination of the interfering nuclides mentioned above is dispensed with. This version can also be used for gross α-activity measurements in a liquid scintillation counter. With the preparation procedures described here the sample volume is limited to 1 ml. Therefore it is preferably applied to medium-active samples from nuclear power plant waste stream, but it can also be used for low-level environmental samples after suitable preconcentration procedures.

Simultaneous determination of environmental α-radionuclides using liquid scintillation counting combined with time interval analysis (TIA) and pulse shape discrimination (PSD)

Some improvements of the detection sensitivity in pulse time interval analysis (TIA) based on selective extraction of successively α-α correlated decay events within millisecond order from random or background events, were established by the utilization of PSD, to reject β/γ-pulses from α-ones and a simple chemical procedure of radium separation, together with the use of well resolved scintillator. By applying the PSD, the contribution of β-decay events was completely eliminated in both the α-spectra and the TIA distribution curves as well as the improvement into clear energy resolution and the enhancement of detection sensitivity for the TIA. As a result, the TIA and α-spectrometric analysis of226Ra-extract showed the existence of223Ra (Ac-series) and β/α-correlated events with correlated life (due to 0.16 ms due to214Bi(β)→214Po(α)→) along with a singly well resolved α-peak to be useful for the determination of226Ra (U-series). The difference of half-lives (145 and 1.78 ms) due to216Po and215Po (direct daughters of224Ra for Th-series and223Ra for Ac-series, respectively) was also proven for the possibility of the simultaneous determination of both correlated events by using the TIA/PSD combined with chemical separation and liquid scintillation counting method. Finally, the simultaneous determination of three natural decay series, which include U-, Th- and Ac-series nuclides, have been conveniently carried out for some environmental samples using the present method combined with225Ra yield tracer (Np-series).

Determination of 234Th in Marine Samples by Liquid Scintillation Spectrometry

A liquid scintillation spectrometry method for the determination of (234)Th in seawater with (230)Th as the yield tracer has been developed and validated. (234)Th is separated from the dissolved phase by an Fe(OH)(3) precipitation and is then purified using ion exchange chromatography. The counting source is prepared by taking the sample to dryness in a vial, redissolving in acid, and mixing with a scintillation cocktail. The instrument employed has a relatively low background (11 cpm) and the ability to separate α from β activity on the basis of pulse shapes. The (234)Th + (234m)Pa counting efficiency is 50% over the counting window employed. The limit of detection, using the above parameters, a 20 L sample, and a 400 min count is found to be 0.04 dpm L(-)(1). It was also demonstrated that less advanced instruments, without α/β separation, can also be used effectively.

Simultaneous measurement of 226Ra and 133Ba using liquid scintillation counting with pulse shape discrimination

The simultaneous counting of 226Ra from environmental samples and 133Ba added as a yield tracer is described. A liquid scintillation counter with pulse shape discrimination was used. The 226Ra decay emissions were recorded in the α-multi-channel analyser (α-MCA) and the 133Ba emissions simultaneously recorded in the β-multi-channel analyser (β-MCA) using experimentally determined discriminator settings. The 226Ra α-decay products were counted after four weeks ingrowth with an optimum counting efficiency of 250% (2.5 cps Bq −1) and an α-background of 0.002 cps within the channels corresponding to 300–900 keV. Emissions resulting from decay of 133Ba by electron capture, and the two emissions produced by the β-decay of the 214Pb and 214Bi daughters of 226Ra were counted in the β-MCA. The 133Ba decay products were counted with an efficiency of 7% (0.07 cps Bq −1) in the channels of the β-MCA corresponding to 1–50 keV. The ratio of counts from 226Ra in these channels to the counts from 226Ra in the 300–900 keV range of the α-MCA was found experimentally to be 0.148 over a broad range of 226Ra activities. In analyses the 133Ba yield tracer was added to each sample before radiochemical separation in preparing for liquid scintillation counting. Counts in the α-MCA were used as a measure of the 226Ra activity, then this was used to estimate the 226Ra β-contribution and hence the net count rate of 133Ba. Comparison of the 133Ba count rate with the standard addition was finally used to correct the 226Ra α-count for recovery. Addition of 10 Bq of 133Ba gave counting errors of about 1%. The simultaneous counting of 133Ba and 226Ra is simpler than separate counting of the 133Ba by γ-spectrometry using Nal or Ge detectors.

Magnetic recovery of radium, lead and polonium from seawater samples after preconcentration on a magnetic adsorbent of manganese dioxide coated magnetite

Ra, Pb and Po were preconcentrated from seawater samples by addition of a magnetic adsorbent followed by mixing and collection of the adsorbent using a magnet. The magnetic adsorbent is prepared by coating micron sized magnetite particles with manganese dioxide. When yield tracers ( 133Ba for 226Ra, 208Po for 210Po and stable lead for 210Pb) were added to small seawater samples, recoveries of the tracers were better than 90% with quantitative recovery of the manganese dioxide adsorbent. For large (401) samples of ocean water, processed on board ship, recovery of the manganese dioxide adsorbent was 70–100%. Recovery of 133Ba (35%) and stable lead (80%) was adequate for measurement of 226Ra and 210Pb in the water. Recovery of 208Po was not satisfactory under the conditions used. The magnetic adsorbent of MnO 2 on magnetite is easy to prepare and allows simple and rapid processing of large water samples at sea.

Standardisation and measurement of the decay scheme data of 243Am and 239Np

243Am is of great importance as a chemical yield tracer for the radiochemical determination of 241Am in environmental and other samples. 239Np can also be used in a similar fashion for 237Np, although there are significant limitations because of the short half-life. The use of both of these radionuclides has been inhibited by the absence of accurately standardised solutions and the poor quality of the associated decay data, particularly the γ-ray emission probabilities for 239Np. Standardised solutions of 239Np alone and of an equilibrium mixture of 243Am and 239Np have been prepared, and these solutions have been used in conjunction with an intrinsic Ge spectrometer to measure the relevant γ-ray emission probabilities.

Metrology of plutonium for environmental measurements

Since its discovery in 1940, plutonium has become widely distributed in the world's environment by a number of routes. Due to the perceived hazard of the element, considerable resources have been devoted to the measurement of plutonium in nuclear waste, nuclear effluent, human beings and the environment. Plutonium is, however, difficult to measure because all of the commonly encountered isotopes have very low abundance γ-ray emissions making conventional absolute 4πα-γ-coincidence counting techniques impractical for the nuclides 236Pu, 238Pu, 239Pu, 240Pu, 242Pu and 244Pu. Instead, the technique of using a tracer nuclide (in this case 241Am) has been employed at the National Physical Laboratory (NPL) to standardize 239Pu and 242Pu and is applicable to the other isotopes mentioned above. 241Pu has some different problems in that it is a ß-emitter with a low (∼20 keV) end point energy and, again, no associated γ-ray. It decays to 241Am which can be measured quite easily, but to achieve calibration by ingrowth with an acceptable uncertainty could take many years. 241Pu is calibrated using liquid scintillation counting by comparison with aqueous 3H, with some corrections made for differing end point energies and β spectrum shapes. In recent years, the technique of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been applied to the field of plutonium measurement and it appears to offer advantages in the routine, high-throughput analysis of plutonium. However, work commissioned by NPL suggests that there are significant problems in the calibration of ICP-MS equipment, with large variations in the response obtained from different plutonium nuclides. In the U.K. measurement community, the most pressing need is for suitable matrix reference materials and standardized chemical yield tracers, incorporating 236Pu, 242Pu or 244Pu. Each of these have some problems in that they are difficult to produce or procure and that isotopic purity can be a problem. The questions to be asked here are; “Is there a continuing global demand for these yield tracers?” if so “Who is prepared to fund production and purification?” and “Are National Standards Laboratories prepared to take on such work?”. These questions and some possible answers will be discussed in the paper.

New radiochemical procedures for environmental actinide measurements and data quality control

Suitable separation techniques were prepared for actinide, 90St and 226Ra determinations in environmental and industrial samples. Extraction chromatography with tri-n-octyiphosphine oxide (TOPO) and di(2-ethylhexyl) phosphoric acid (HDEHP) solutions was, used. In some cases, a powder of Microthene (Microporous polyethylene) supporting solid TOPO was prepared thus obtaining a material showing better storing and column preparation features. Uranium and 226Ra were determined in phosphorites, phosphoric acid and phospbogypsam. Uranium, thorium and 226Ra were also measured in the low specific activity scales of hydrocarbon production equipment: 226Ra was found to concentrate in some parts of the plant so causing a radiation protection problem. Plutonium and 90St were measured either in some Mediterranean Sea samples or in environmental samples collected in Antarctica. Some interesting sea sediment profiles were also obtained. All the chemical methods were verified by: a) adding some yield tracers (232U, 228Th, 242pu); b) analyzing some certified samples supplied by IAEA and NIST; c) participating in some international intercomparison runs; d) using, when possible, both an analytical and a radiometric method and e) following the radioactivity decay or growth (90y and 226Ra). The determination of actinides in environmental and industrial samples is cf great importance for radiation protection purposes. Plutonium isotope measurements require a perfect separation and prolonged counts by alpha spectrometry; uranium and thorium measurements by gamma spectrometry can give rise to great errors when natural or artificial disequilibria are present or when the radionuclide concentration is low. This being stated, suitable separation techniques were prepared for the determination of the actinides by alpha spectrometry in several kinds of matrixes. 90Sr and 226Ra were also determined in some samples. Extraction chromatography 1 with tri-n-octylphosphine oxide (TOPO) and di(2-ethylhexyl) phosphoric acid (HDEHP) supported on microporous polyethylene (Microthene) was mainly used. The chemical procedures were verified by one or more of the following data quality control methods: a) by adding some yield tracers (232U, 228Th, 242pu); b) by analyzing some certified samples supplied by IAEA and NIST; c) by participating in some international intercomparison runs; d) by using, when possible, both an analytical and a radiometric method; e) by following the radioactivity decay or growth (90y and 226Ra).

The separation of 99Tc from low and medium-level radioactive wastes and its determination by inductively coupled plasma mass spectrometry

A chemical separation method has been developed for the determination of 99Tc in various types of radioactive wastes. Such a method includes (i) fusion with NaOH, (ii) extraction in a column containing methyltrioctylammonium chloride, (iii) extraction by solvent with N-benzoyl- N-phenylhydroxylamine and, (iv) measurement by inductively-coupled plasma mass spectrometry (ICP-MS). From the performance standpoint, the recovery of 99Tc, using 99mTc as a yield tracer, is higher than 70%. This analytical method, as developed, ensures effective decontamination with respect to the radionuclides, insofar the decontamination factors are greater than 10 +5, whenever the residual activity may be measured. Taking into account a 3σ counting error, the detection limit obtained with the ICP-MS technique is 1.9 mBq/ml; the method enabling hence to detect activities as low as 0.3 Bq/g, with analysed samples of 0.2 g and a radiochemical yield of 70%. Studies have been dedicated to the 99Tc measurement, using the electrothermal vaporization ICP-MS technique, which lowers the detection limit by a factor 10, with the standard solution (0.3 pg/ml), compared with the previous ICP-MS technique.

A new very sensitive LSC procedure for determination of Tc-99 in environmental samples

A new method for the determination of Tc-99 in different environmental samples has been developed. The sample is carefully ashed in a muffle furnace and then fused with Na2CO3 and K2CO3. The first step is an enrichment and purification of TcO 4 − on an anion exchange resin. The Tc is desorbed as a cationic thiourea complex, which is held on a cation exchange resin. The complex is destroyed by oxidation to TcO 4 − with (NH4)2S2O8 in sulfuric acid. From this solution TcO 4 − is extracted into TBP/toluene and the organic phase is mixed with a scintillation cocktail and counted in an anticoincidence shielded LSC. Tc-99m is used as a chemical yield tracer. The decontamination factors for all important fission and activation products and naturally occurring radionuclides are in the range between > 105 and > 108. The detection limit is about 5 mBq per sample at a counting time of 1000 minutes. The maximum sample amount of plants is 500 g dry weight and therefore the lowest detection limit achievable is 10 mBq/kg. Ashing and dissolution of the samples takes 24 h and 4 analyses are performed by one technician in 8 hours. The chemical yield ranges from 50 to 80%.

Separation of Ra and Th from rock matrices for alpha-spectrometry

Dating rocks using226Ra/230Th isochrons demands radiochemical purification of radium and thorium. This paper presents an improved method. Rocks are solubilised by nitric/nydrofluoric digestion followed by dissolution of insoluble fluorides by boric/nitric acids, and Th is extracted by passing the 8M nitric solution through an anion column in nitrate form. The eluant contains Ra and Ba which are precipitated as sulphate and redissolved in alkaline EDTA. Complete separation of Ba and Ra from sulphate is on an AG 1×8 anion column in EDTA form, which was found better than the chloride form. The Ba+Ra is separated on an AG 50W×8 cation column, and uses CDTA as an eluant for Ba. Careful pH control is essential. Ra elutes later with EDTA or 4M HCl and is precipitated with 125 μg barium as sulphate to yield a source suitable for α-spectrometry, or further treated to electroplate the Ra. The yield tracers used are228Th and224Ra. Because the sample contains natural224Ra a correction must be applied, calculated from the amount of natural232Th in the Th spectrum. Th may be precipitated with 100 μg of ferric iron and gives a spectrometry-quality source, but further purification and electrodeposition was found to be preferable. Variations on the method for the case of analysis of calcium-rich fish otoliths are described.

Interlaboratory comoparison of analytical methods for the determination of natural series uranium and thorium isotopes in rock samples

Results are repoerted for238U,234U,232Th, and230Th determinations in 19 rock samples from a uranium mine, performed independently, byb three different laboratories. Uranium and thorium isotopoic activities were determkined by alpha spectrometry, after different pre-concentration and counting sample preparation techniques., Additionally, total concentrations of uranium were determined by fluorimetry and gamma spectreometry. the folloing conclusions could be drawn from this intercomparison test: (1) The results for238U specific activity agreed with the amjority of results within 10%. Lincar correlation coefficients between the three data sets were 0.999. However, for a few samples of much higher uranium concentrations, large deviations were observed, indicating problems of, sample heterogencity. (2) For the234U/238U activity ratio data, a still closer agreement was obtained (5%), as computation of the activity ratios did not, require information on the yield of the used tracer spike (232U). (3) The results for232Th specific activities and230Th/234U activity ratios showed larger deviastions between the three laboratories (typically up to 15%, in some cases still ore). Different Th-isotopes (228Th,234Th and229Th) have been used as yield tracers. The data indicates, however, that the observed deviations are not simply a consequence of a systematic difference in the calibration of the different spikes, but, probably cased by other errors such as incomplete sample dissolution, sample heterogencity, tec. The limitations of alpha spectrometry will be discussed and an application of the developed methods shown.

An efficient quantitative technique for the simultaneous analyses of radon daughters 210Pb, 210Bi and 210Po

An improved and time efficient technique has been developed for quantitative determination of the long-lived 222Rn daughters ( 210Pb, 210Po and 210Bi) in atmospheric and oceanic samples. The sample is first spiked with yield tracers for polonium (208 or 209), bismuth (207), and lead (stable lead carrier). These nuclides may then be scavenged through iron hydroxide precipitation and redissolved in a dilute (pH ∼ 2) nitric acid plating medium with citrate and hydroxylamine hydrochloride at 90° centrigrade with constant stirring. First a silver planchet is suspended in the solution which plates polonium to high efficiency. Second, a nickel planchet is suspended in the same solution which is maintained hermetic ( e.g. bubbling with helium) and bismuth is plated next with high efficiency. Third, lead is purified from the same solution using anion exchange techniques and isolated for beta counting as the sulfate. Polonium is analyzed by isotope dilution alpha spectrometry. Bismuth and lead are analyzed by anti-coincident beta counting in a low level shield. In the case of bismuth, the 207 tracer is added in quantities at least comparable to the background of the beta system such that counting before and after the decay of 210Bi gives the bismuth yield. The unique characteristics of this technique are its speed and efficiency; all three radon daughters can be isolated for counting within 4 hr of pre-treating the sample. The remaining solution can be treated subsequently for other analyses as appropriate.