Alpha Spectrometric Measurements Research Articles

An improvement in the small-volume technique for determining thorium-234 in seawater

The recently developed 2–5 L small-volume MnO 2 coprecipitation method for determining 234Th in seawater has provided a new way to substantially increase, both temporally and spatially, the sampling resolution of 234Th and 234Th-based particulate organic carbon export estimates in the upper ocean. In this study, we further optimize the technique by reducing reagent quantities and the use of an additional water bath heating step. This optimization allows the filtration of the MnO 2 precipitate onto a 25-mm diameter, 1.0 μm pore size QMA filter to be completed within < 30 min for unfiltered waters from the South China Sea. In addition, we have modified the MnO 2 purification procedure to allow for alpha spectrometric measurements of 234Th recoveries. Results from recovery experiments suggest that reagent amounts can be reduced to 0.0375 mg KMnO 4 and 0.1 mg MnCl 2·4H 2O per liter of sample, while still maintaining high 234Th recovery. This study further confirms that the addition of a yield monitor is necessary for the application of the small-volume method.

Method to determine the nuclide inventory of low-activity waste of the RBMK-1500 reactor

Results of experimental and modelling evaluation of scaling factors for difcult-to-measure radionuclides in the Ignalina Nuclear Power Plant (INPP) waste are of primary importance in solving the decommissioning problems. The peculiarities of experimental measurements with radiochemical preparation of investigated INPP samples, the analysis of performed alpha, beta, and gamma spectrometric measurements, the theoretical evaluation and estimation of scaling factors, and nally a simplied method of determining the nuclide inventory for very-low-activity waste are presented in this work.

Optimization of 210Pb determination via spontaneous deposition of 210Po on a silver disk

The accuracy of 210Pb determination via spontaneous deposition of 210Po on a silver disk and alpha spectrometric measurement was examined. The study focused on the storage conditions of the polonium-containing solutions, the tracer used in polonium analysis and the effect of storage time and acid concentration on 210Po deposition. The intermediate precision and repeatability associated with the improved 210Pb analysis of fresh groundwater samples was 5 and 14%, respectively. These improved values were achieved by using glass bottles as storage containers for the solution remaining from the first 210Po deposition, by rinsing the sample container with concentrated hydrochloric acid after storage and by using different isotopes of polonium as the yield determinant tracer in the first and the second deposition. Less polonium adsorption onto the storage container walls occurred with HCl than with HNO 3. The overall uncertainty in 210Pb analysis was (11 ± 7)% at the 95% confidence level. The minimum detectable activity concentration was 0.1 mBq l −1 calculated from blank samples and 0.05 mBq l −1 using the background counts of the alpha spectrometer.

Traceability of radon-222 activity concentration in the radon chamber at the technical university of Catalonia (Spain)

In order to provide reference 222 Rn activity concentration, a device based on the alpha spectrometric measurement of 218 Po collected electrostatically on a PIPS detector, has been developed and characterised. Traceability is achieved by the use of primary 222 Rn standard activity inside a glass bulb obtained from the Physikalisch–Technische Bundesanstalt. Radon standard activity is then transferred to the instrument that measures the reference radon activity concentration. The instrument is used in the walk-in radon chamber of the Institute of Energy Technology at the Technical University of Catalonia in order to provide a reference atmosphere for the calibration of radon concentration detectors. Under typical environmental calibration conditions within the radon chamber, an expanded uncertainty of roughly 4% ( k=2) for radon concentration is usually estimated.

Study on geochemical association of plutonium in soil using sequential extraction procedure

Three kinds of soil, collected in various places (in northwestern and southeastern Poland and near Chernobyl) were used as a subject of sequential extraction and plutonium distribution study. The modified method of Tessier was applied to separate readily available, carbonate, organic, Fe/Mn oxide and residual fractions. Plutonium isotope activity in soil as well as in particular separated fractions was determined by means of alpha spectrometry. The method of plutonium separation and purification for alpha-spectrometric measurements was modified according to the chemical properties of the extracted fraction. It was found that the major part (about 90%) of 239,240Pu is bound to organic and Fe/Mn oxide fractions (in uncultivated soil samples of northwestern Poland and Chernobyl). In soil samples coming from river valley (southeastern Poland) almost equal amounts of plutonium are distributed between the available, organic and residual fractions.

Concentrations and activity ratios of uranium isotopes in the groundwater of the Okchun Belt in Korea

Groundwater samples obtained from the Okchun Belt in Korea were separated into particulate and filtered fraction using a 0.45 μm membrane filter and concentrations and activity ratios of uranium isotopes in the fractions were determined by chemical separation and alpha-spectrometric measurements. Most of the uranium isotopes in the groundwater were found in the filtered water. Only less than 1% of the total uranium was detected in the particulate fraction. The concentrations and activity ratios of uranium isotopes in the groundwater measured in this study were variable, depending upon sampling site. Owing to a rapid material exchange between the subterranean hot waters and the rock strata, the concentrations of 238U in the groundwater in the hot spring area were found to be about four times higher than those elsewhere. Because of the α-particle recoil effect, the activity ratios of 234U/ 238U in the groundwater taken at “cold” spring sites were variable within the range 1.20 to 3.58, depending on the residence time of the groundwater. In the hot spring area, the activity ratios of 234U/ 238U were close to the equilibrium value (1.10±0.07) due to rapid erosion of the rock strata by the hot spring water.

Determination of [formula omitted] and [formula omitted] in water using a large volume ionisation chamber

A new method for measuring 222 Rn and 226 Ra in water has been devised. It is based on exhaling radon to a void volume by continuous bubbling of air through the water. The exhaled radon is then transferred in a closed circuit to a modified radon gas pulse ionisation chamber for alpha-spectrometric measurements. About 86% of the radon in water is transferred from 0.75 l of water to the void volume (3.2 l). The set-up offers direct and specific 222 Rn measurements for a wide range of concentrations and shows a low detection limit (LLD=45 mBq l −1 for 8 h counting time). Radium in water is measured, via radon, after sample storage for a month. The method was compared with gamma ray spectrometry for radon and for radium, the latter after pre-concentration by co-precipitation with MnO 2 from 10 l water samples. An excellent agreement between the two techniques was obtained. As a part of a radon survey, the method was employed for analysis of drinking water from bedrock wells.

Environmental Radioactivity Measurements of Egyptian Soils

Soil and vegetation samples from 33 sites within the northwestern area of the River Nile delta in Egypt have been analyzed for natural and man-made radioactivity. Gamma-ray spectrometric measurements were performed where 214Bi and 214Pb were used for 238U-series determinations, while 208Tl and 228Ac were used for 232Th-series determinations. In addition, alpha-spectrometric measurements were also performed for the determination of different isotopes of uranium and plutonium. Other parameters examined included the determination of radium equivalent activities and relationship between the gamma-radiation values and subsequent dose level determinations and the soil types.

Non-destructive gamma spectrometric U-series dating

Prehistoric hominid fossils are too valuable to be dated by destructive or even partially destructive methods. Non-destructive U-series dating by γ-ray counting can therefore be a valuable method if relatively large hominid fragments, such as skulls, containing measurable amounts of uranium are available. We present a description of the method as well as some results including those obtained from a previously dated coral as well as two Australian hominid skulls (WLH 50 and Mungo 3). The dating procedure is designed to minimise systematic errors which may easily overwhelm statistical errors if care is not taken. The gamma spectrometric results are in good agreement with alpha and mass spectrometric measurements as well as independent age determinations. The results show no evidence for any uranium uptake over longer time periods.

Optimization and characterization of a sulfate based electrodeposition method for alpha-spectroscopy of actinide elements using chemometric analysis

Alpha-spectrometric measurements using Si detectors is the standard method for the determination of alpha emitting actinide elements. This method requires the preparation of sources for analysis which do not degrade the energy spectrum of the emitted alpha particles via sample self-absorption. A variety of methods for the electrodeposition of actinides have been reported in the literature, many of which require long deposition times and lack reproducibility. A sulfate based method has been evaluated for the preparation of these sources using chemometric analysis to optimize the method and evaluate several variables and their interactions with the goal to achieve high yield source preparation in 1 hour or less. Typical resolution for this method is 30 keV or less with recoveries approaching unity.

226Ra in tap and mineral water and related health risk in the republic of Croatia.

The presence of 226Ra in drinking water may sometimes make important contribution to natural background radiation exposures. The paper describes the study of 226Ra content in drinking water of Croatia: tap water from the public supply system of several major towns and bottled mineral water from two selected mineral water springs. 226Ra was determined by alpha-spectrometric measurement after radiochemical separation. The radiation doses originating from drinking tap water and bottled mineral water were estimated. The annual dose from consumption of bottled mineral water was compared to that received from ingestion of public system tap water. The study showed that 226Ra content for investigated categories of waters is below the levels at which any unacceptable dose due to ingestion would arise.

An analysis of efficient measurement procedures for radon progeny

Efficient measurement procedures for 222Rn- and 220Rn-progeny are needed for dose mitigation in the important field of indoor radiation exposure. Practical and instrumental measurement parameters are discussed. In the light of these, the measurement efficiency of batch and continuous sampling procedures for individual radon progeny, including flow-through, alpha spectrometric and beta measurement, was investigated. Measurement standard deviations were derived at normalized progeny concentrations, flow-rate, and collection and detection efficiencies. These can readily be converted to other than the chosen normalized conditions. The standard deviations and total procedure time are useful indications of measurement efficiency. Combined beta/alpha detection with modern Si detectors offers greatly improved measurement efficiency over conventional alpha detection, which is advantageous particularly when measuring generally low environmental radiation levels. This combination makes feasible much shorter total times for batch procedures or shorter time differentiation for continuous procedures and far more convenient, portable instruments. For 222Rn progeny and mixtures with 220Rn progeny, similar advantages are attained over alpha-only procedures.

Determination of isotopes of uranium and thorium in low-level environmental samples

Different sample treatments and separation procedures are set up and compared for the analysis of uranium and thorium in coal, sediments, water and plant samples. Some considerations about the alpha-spectrometric measurements and the radioactive tracers used as yield determinants of the chemical process are presented.

Optimal Method for Environmental Radon and Thoron Daughters Determination by Alpha Spectrometry

In this work the least squares method is applied to the determination of environmental radon and thoron daughters in the case of repeated alpha spectrometric measurements of aerosol samples collected on a filter. The dependence of the uncertainty of the results upon the parameters involved is reported; in the derivation the results of a careful study of the stochastic processes related to the retention of aerosols and the disintegration of radionuclei are included. Optimal values for the parameters are recommended.

Determination of Pu in environmental soil using238Pu as a yield tracer

A procedure for determining Pu in environmental soil using238Pu as a yield tracer is described. The method involves radiochemical separation and electrodeposition onto a stainless steel disc followed by alpha-spectrometric measurement with a solid-state detector. In order to eliminate error in calculation caused by238Pu contained in original samples, a new calculating method is introduced in this paper. By using this method, the activity of238Pu contained in original samples can be substracted from the total activity of samples, to which the238Pu tracer is added. This procedure has been applied satisfactorily to the determination of Pu in a soil reference sample, which was supplied by the Institute of Metrological Science of China.

Analysis of uranium and plutonium materials by radiometric methods

The radiometric methods used in the IAEA Safeguards Analytical Laboratory for the analysis of uranium-and plutonium-containing materials sampled in nuclear facilities under IAEA Safeguards are presented. Uranium-235 concentrations are determined in solutions by intensity measurements of the 185.7-keV γ rays with a scintillation detector. The factors affecting the accuracy of results, e.g. dead time and self-absorption corrections, background subtraction, and calibration procedure are discussed. When all these factors are properly taken into account the standard deviation of measurement approaches the value resulting from counting statistics. The 238Pu content in freshly separated plutonium solutions is measured by α-particle spectrometry in combination with mass spectrometry. The alpha sources are prepared by evaporation of analyte solution with tetraethyleneglycol on glazed porcelain discs and subsequent ignition at 850°C. The alpha-spectrometric measurement is performed using the spectrometer with a surface-barrier detector. The alpha-activity ratio of 238Pu to 239 Pu+ 240 Pu is calculated taking into account the tailing correction for 238Pu under the 239 Pu+ 240 Pu peaks. The two methods of tailing correction are described: (i) exponential fitting, and (ii) geometric progression. The atomic ratio of 238Pu/ 239Pu peaks is derived from the alpha activity, and finally, the 238Pu abundance is calculated using the values for 239Pu and 240Pu contents from mass-spectrometric measurement. Plutonium isotopic composition, elemental concentration of Pu, 241Am, 237Np and 235U/Pu ratio are assayed using a γ-ray spectrometer with a high resolution planar germanium detector. A set of computer programs is used for spectral evaluation and calculation of respective concentrations. The results obtained on a number of samples using this method are compared with those of other methods.

Comparability of data for natural radionuclides in marine sediment obtained by different analytical techniques

In the paper are presented results of potassium, uranium, thorium and radium measurements performed on the natural marine sediment sample SD-N-1/2 in the framework of the IAEA-organized worldwide intercomparison exercise. Analytical methods applied in this exercise were evaluated for performance and significance of the observed discrepancies are discussed in the light of statistical and operative criteria. Possible sources of error have been identified in alpha and gamma spectrometric measurements and suggestions are given about how to avoid them. Well characterized reference materials based on natural matrices have been shown helpful in achieving better data comparability in low level measurements of environmental radioactivity.

Simple collection and direct alpha-spectrometric determination of214Pb and214Bi in natural water

A rapid method has been developed for the de termination of214Pb and214Bi in natural waters by alpha-spectrometric measurement of214Po. Well water was filtered on a membrane filter impregnated with manganese oxide and followed by direct alpha-spectrometric analysis. A prominent alpha peak was assigned to214Po, which should be supported by the longer lived parents214Pb and214Bi. The activity ratios between214Pb and214Bi adsorbed on the filter were determined by using the change of activity of214Po as a function of counting period after the filtration. The adsorbed yield of214Pb was also determined from the growth of the alpha-peak due to210Po from a210Pb tracer added in the original water. The results indicated that the amount of214Pb was in radioactive non-equilibrium state with the Rn-222 dissolved, while the activity ratios of214Bi/214Pb showed on increasing tendency with the storage period of the water.

Review of chemical separation techniques applicable to alpha spectrometric measurements

Prior to alpha-spectrometric measurements several chemical manipulations are usually required to obtain alpha-radiating sources with the desired radiochemical and chemical purity. These include sampling, dissolution or leaching of the elements of interest, conditioning of the solution, chemical separation and preparation of the alpha-emitting source. The choice of a particular method is dependent on different criteria but always involves aspects of the selectivity or the quantitative nature of the separations. The availability of suitable tracers or spikes and modern high resolution instruments resulted in the wide-spread application of isotopic dilution techniques to the problems associated with quantitative chemical separations. This enhanced the development of highly elective methods and reagents which led to important simplifications in the separation schemes. The chemical separation methods commonly used in connection with alpha-spectrometric measurements involve precipitation with selected scavenger elements, solvent extraction, ion exchange and electrodeposition techniques or any combination of them. Depending on the purpose of the final measurement and the type of sample available the chemical separation methods have to be adapted to the particular needs of environment monitoring, nuclear chemistry and metrology, safeguards and safety, waste management and requirements in the nuclear fuel cycle. Against the background of separation methods available in the literature the present paper highlights the current developments and trends in the chemical techniques applicable to alpha spectrometry.

Radioisotope dilution analyses of geological samples using 236U and 229Th

The use of 236U and 229Th in alpha spectrometric measurements has some advantages over the use of other tracers and measurement techniques in isotope dilution analyses of most geological samples. The advantages are: (1) these isotopes do not occur in terrestrial rocks, (2) they have negligible decay losses because of their long half lives, (3) they cause minimal recoil contamination to surface-barrier detectors, (4) they allow for simultaneous determination of the concentration and isotopic composition of uranium and thorium in a variety of sample types, and (5) they allow for simple and constant corrections for spectral inferences, 0.5% of the 238U activity is subtracted for the contribution of 235U in the 236U peak and 1% of the 229Th activity is subtracted from the 230Th activity. Disadvantages in using 236U and 229Th are: (1) individual separates of uranium and thorium must be prepared as very thin sources for alpha spectrometry, (2) good resolution in the spectrometer system is required for thorium isotopic measurements where measurement times may extend to 300 h, and (3) separate calibrations of the 236U and 229Th spike solution with both uranium and thorium standards are required. The use of these tracers in applications of uranium-series disequilibrium studies has simplified the measurements required for the determination of the isotopic composition of uranium and thorium because of the minimal corrections needed for alpha spectral interferences.