Radioanalytical methods for the accurate determination of227Ac and228Th in irradiated226Ra targets

Alpha spectrometry is proposed for the quantitative analysis of²²⁷Ac and²²⁸Th in irradiated²²⁶Ra targets. The chemical separation and the radiochemical determination is described.     

A multi-element serum standard for neutron activation analysis

An annular ²²⁷AcBe isotopic neutron source, containing 6.6-Ci ²²⁷Ac, is described for application in fast and thermal neutron activation analysis, with high accuracy, for major constituents in ores, alloys and industrial concentrates. The characteristics of the neutron output and of the fast, epithermal and thermal flux and flux gradients is described in detail. The determination of manganese in pyrolusite ores and ferro-manganese is compared to results obtained previously with a cylindrical 1-Ci ²²⁶RaBe source. Two new sources of systematic errors have been discovered.     

Contribution to the simultaneous determination of228Ra and226Ra by using 3M's EMPORETM radium rad disks

New method for simultaneous determination of²²⁸Ra and²²⁶Ra by using 3M's EMPORE^TM Radium Rad Disks in water has been developed. Both radionuclides²²⁶Ra and²²⁸Ra were counted through their daughter products,²²⁶Ra by conventional radon emanation techniques and²²⁸Ra through its daughter²²⁸Ac by using a proportional counter. Different molarity of diammonium hydrogen citrate were used for elution of²²⁸Ac and²²⁶Ra from EMPORE^TM Radium Rad Disks. 79% of²²⁸Ac was eluted in 10 ml of 0.0003M diammonium hydrogen citrate. The recovery of²²⁶Ra was 99% by using 40 ml of 0.2M diammonium hydrogen citrate adjusted by ammonium to pH 7.8.     

Non-destructive determination of low-level210Pb and226Ra with an ordinary high-purity Ge-detector

A convenient non-destructive method for the determination of low level²¹⁰Pb and²²⁶Ra with an ordinary high-purity Ge-detector is presented. The ordinary Ge-detectors used in this work were available to measure 46.5 keV -rays of²¹⁰Pb. These detectors were also useful for the non-destructive analysis of low-level²²⁶Ra in lime-stone and calcium chemicals when a stream of nitrogen gas was maintained around the detectors. By this method, measurements could be carried out not only for²¹⁰Pb and²²⁶Ra but also for other -emitting radionuclides simultaneously, using the same detector. The detection limits of about 1 Bq per sample for²¹⁰Pb and about 0.05 Bq per sample for²²⁶Ra, respectively, were estimated, when the samples were counted for 1–2 days.     

Rapid method for 226Ra and 228Ra analysis in water samples

Summary The measurement of radium isotopes in natural waters is important for oceanographic studies and for public health reasons. Radium-226 (T_1/2 = 1620 y) is one of the most toxic of the long-lived alpha-emitters present in the environment due to its long life and its tendency to concentrate in bones, which increases the internal radiation dose of individuals. The analysis of ²²⁶Ra and ²²⁸Ra in natural waters can be tedious and time-consuming. Different sample preparation methods are often required to prepare ²²⁶Ra and ²²⁸Ra for separate analyses. A rapid method has been developed at the Savannah River Environmental Laboratory that effectively separates both ²²⁶Ra and ²²⁸Ra (via ²²⁸Ac) for assay. This method uses MnO₂ Resin from Eichrom Technologies (Darien, IL, USA) to preconcentrate ²²⁶Ra and ²²⁸Ra rapidly from water samples, along with ¹³³Ba tracer. DGA Resin^ò (Eichrom) and Ln-Resin^ò (Eichrom) are employed in tandem to prepare ²²⁶Ra for assay by alpha-spectrometry and to determine ²²⁸Ra via the measurement of ²²⁸Ac by gas proportional counting. After preconcentration, the manganese dioxide is dissolved from the resin and passed through stacked Ln-Resin-DGA Resin cartridges that remove uranium and thorium interferences and retain ²²⁸Ac on DGA Resin. The eluate that passed through this column is evaporated, redissolved in a lower acidity and passed through Ln-Resin again to further remove interferences before performing a barium sulfate microprecipitation. The ²²⁸Ac is stripped from the resin, collected using cerium fluoride microprecipitation and counted by gas proportional counting. By using vacuum box cartridge technology with rapid flow rates, sample preparation time is minimized.     

Measurement of the radioactivity of238U,232Th,226Ra,137Cs and40K in soil using direct Ge(Li) γ-ray spectrometry

Radioactivity of the nuclides²³⁸U(²³⁵U),²³²Th,²²⁶Ra,¹³⁷Cs and⁴⁰K was measured in soil by direct -ray spectrometry using Ge(Li) detector. Relative laboratory method was used. Soil was dired, powdered, sieved and put into hemetically sealed container. CCRMP certified reference materials and compounds of the above nuclides mixed with fine quartz sand were used as references. Five and four -lines were used for the determination of²³²Th and²²⁶Ra, respectively, to obtain more accurate results. The most significant interferences, caused by the limited energy resolution of the detector, were resolved. In the case of ordinary soils, using one day duration of measurement and 1 kg mass of soil,²³²Th,²²⁶Ra and⁴⁰K can be determined with less than 10% relative random error. Elevated concentrations of²³⁸U(²³⁵U) and²²⁶Ra were observed in soil samples collected around a coal-fired power plant in Ajka town, Hungary.     

Assessment of 226Ra and 228Ra activity concentration in west coast of India

An investigation on the distribution of ²²⁶Ra and ²²⁸Ra activity concentration in coastal surface sea water from Okha in Gujarat to Ratnagiri in Maharashtra state along the west coast of India was carried out. In-situ pre-concentration technique was used to measure radium isotopes by passing 1,000 L of seawater through MnO₂ impregnated polypropylene filter cartridges at all the locations. ²²⁶Ra was estimated using gamma ray peak of its daughter radionuclides ²¹⁴Bi and ²¹⁴Pb. ²²⁸Ra was estimated from its daughter ²²⁸Ac. In the coastal waters, ²²⁶Ra and ²²⁸Ra activity concentration were observed to be in the range of 1.5–2.9 and 2.5–8.6 Bq m^?3 with a mean of 2.2 and 4.9 Bq m^?3 respectively. The activity of ²²⁸Ra was observed to be more than ²²⁶Ra in all the locations. The variation in spatial distribution of the radium isotopes activity concentration and its ratio with respect to location is discussed in the paper. The radioactive database obtained represents reference values for coastal environment of India.     

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).     

Determination of228Ra in drinking water

A procedure for the analysis of²²⁸Ra in drinking water has been developed. The procedure involves separation of radium by an initial coprecipitation with lead sulfate. The isolated Pb(Ra)SO₄ is then dissolved in sodium diethylenetriamine pentaacetate (DTPA). Radium-228 is co-precipitated from this solution with barium sulfate while the DTPA supernate which contains pre-existing²²⁸Ac is discarded. The purified Ba(Ra)SO₄ precipitate is then allowed to ingrow, generating²²⁸Ac, which is then dissolved in DTPA, isolating both²²⁶Ra and²²⁸Ra in the precipitate while²²⁸ Ac remains in the aqueous supernate. The supernate is partitioned against di-(2-ethylhexyl phosphoric acid), HDEHP, dissolved in n-heptane, which retains the²²⁸Ac. Actinium-228 is then stripped from the organic phase by partitioning against 1M HNO₃. Finally, the²²⁸Ac is coprecipitated onto cerium oxalate. The precipitate is collected on a filter and counted in a low-background beta counter. Radium-228 standards with concentrations ranging from 0.044 to 1.6 Bq were used to establish the detector counting efficiency for²²⁸Ac in cerium oxalate samples, as well as monitoring the chemical yield and absorption factors. The resultant average value of 30.3±2.1 cpm/Bq (uncertainty given at 95% level of confidence) was obtained. Various²²⁸Ra cross checks from U. S. Environmental Protection Agency (EPA) with concentrations of 0.063–0.52 Bq/l were analyzed in order to assess the performance of the procedure. The minimum detectable concentration (MDC) of²²⁸Ra in water with this procedure is 0.015 Bq/l. This is based on a one liter aliquot of sample, a 100 min couting period, and a 3 hour decay interval between the end of²²⁸Ac ingrowth and midpoint of counting. Decontamination factor studies were performed to determine the extent of the carry-over of²³⁸U,²²⁶Ra,²¹⁰Po, and⁹⁰Sr into the final fraction.     

Natural radioactivity levels of limestone rocks in northern Iraq using gamma spectroscopy and nuclear track detector

The activity concentration of radionuclides, such as ²³⁸U, ²²⁶Ra and ⁴⁰K of limestone rocks in northern Iraq was measured using gamma spectroscopy. The radionuclide activities were obtained and discussed. CR-39 nuclear track detector was used to measure the radon exhalation rates as well as the effective radium contents of these samples and are found to correspond with uranium concentration values measured by NaI(Tl) detector in the corresponding limestone rocks samples. The absorbed gamma dose rates in air due to the presence of ²³⁸U, ²²⁶Ra, ⁴⁰K and cosmic ray contribution varied between 105.3 and 223.11 nGy/h. The annual effective dose of each sample has been calculated. The correlation between activities of ²²⁶Ra, ²²²Rn exhalation rates and ²³⁸U is explained. Results show a symmetrical distribution of activity concentrations of primordial of radionuclides in selected samples. The values of all studied radionuclides are considered to be a typical level of natural background and compared with results of similar investigations carried out else where.     

Radiometric determination of226Ra,228Ac and40K in fly-ashes of ČSFR

The subject of this paper was to determine some radionuclides in fly-ashes of Czechoslovak origin.²²⁶Ra,²²⁸Ac and⁴⁰K were chosen because of their high information value. The radiometric measurements were carried out by means of a semiconductor detector.     

Identification and determination of natural radioactive impurities in rare earth chlorides

²²⁷Ac,²²⁸Th,²²⁶Ra,²¹⁰Po and²¹⁰Pb can be present at rare earth chlorides. A radiochemical procedure is presented for the identification and determination of natural radioactive impurities in rare earth chlorides. The determination limits for these radionuclides were 1.5·10^–4 to 3·10^–1 Bq/g. The relative standard deviations for determining 10^–2 Bq/g radionuclides were usually less than ±7%.     

Radioactive series disequilibria in underground uranium deposits of the Singhbhum Shear Zone, Eastern India

Radionuclides of the ²³⁸U series (²²⁶Ra, ²¹⁰Pb, ²³⁴Th and ²³⁴U), ²³⁵U series (²²⁷Ac and ²³¹Pa) and ²³²Th series (²²⁸Th and ²²⁸Ra) series were measured by High Resolution Gamma Spectrometry system in twenty-five uranium ore samples from underground uranium deposits in the Singhbhum Shear Zone of Eastern India. The activity concentrations were observed to vary within a wide range in most of the deposits, as is the case in most rocks of crustal origin. The uranium ore from these deposits were not of high ore grade (U concentrations ranged from 0.015 to 0.082%). Activity ratios of key daughter–parent pairs from the decay chains, viz. ²²⁶Ra/²³⁸U, ²²⁶Ra/²¹⁰Pb, ²³¹Pa/²³⁵U, ²²⁷Ac/²³⁵U, ²³⁰Th/²³⁸U, ²³⁴U/²³⁸U, ²²⁶Ra/²³⁰Th and ²²⁸Th/²²⁸Ra indicated migration/accumulation of uranium and radium in some samples. The ²²⁶Ra/²³⁰Th ARs suggested that the deposits were not closed to groundwater movement for a maximum time period of 8ky. Thiel plot of the ²³⁴U/²³⁸U vs. ²³⁰Th/²³⁸U activity ratios indicated uranium accumulation and complex processes of uranium redistribution.     

The determination of radium-226 and radium-228 in soils and plants,using radium-225 as a yield tracer

Recovery of²²⁶Ra in analysis is determined using²²⁵Ra separated by anion exchange from²²⁹Th and²³³U. Radium is coprecipitated with barium, and purified by ion exchange.²²⁶Ra and²¹⁷At (decay product of²²⁵Ra) are measured by α-spectrometry.²²⁸Ra is determined both by β-counting²²⁸Ac and²²⁵Ac separated from²²⁸Ra and²²⁵Ra, and by α-counting its daughters after the decay of²²⁵Ra. Sources for α-spectrometry are prepared by electrodeposition (molecular plating).     

Direct determination of 226Ra in NORM/TENORM matrices by gamma-spectrometry

Summary The main shortcoming with the procedure to determine ²²⁶Ra in a gamma spectrum of an environmental sample by means of the ²¹⁴Bi and ²¹⁴Pb photopeaks is the likelihood of ²²²Rn leakage from the sample counting vial. An option to make such determination is to disregard the ²²⁶Ra gamma-contributions to the spectrum, other than 186.2 keV (3.5%), subtracting the ²³⁵U contribution to the ²²⁶Ra+²³⁵U peak at 186 keV. The use of this option to determine directly ²²⁶Ra activity concentrations in environmental samples and in NORM/TENORM matrices will be presented and discussed.     

Improvement of quality in the evaluation of radium isotopes 224,226,228Ra in oil scale samples

Elevated concentrations of the radium isotopes ^224,226,228Ra exist in the scale and produced water in oil exploration. The activity concentration of ²²⁶Ra was calculated from 186.2 keV peak with no usual spectral interference of 185.7 from ²³⁵U. The activity concentration of ²²⁸Ra was calculated from its first daughter product ²²⁸Ac using the 911.2 keV gamma rays since it is a pure beta emitter. The activity concentration of ²²⁴Ra was calculated from ²¹²Pb using the 238.6 keV gamma-ray and the secular equilibrium equation with ²²⁸Ra. The IAEA 448 (oil contaminated field soil) reference material was used as a quality control for ^226,228Ra and but was unreliable for ²²⁴Ra using ²¹²Pb.

     

The determination of mercury by non-flame atomic absorption and fluorescence spectrometry.

An isotopic dilution method has been developed for the determination of ²²⁶Ra and ²²⁸Ra in sea water and sediments with ²²³Ra as a yield tracer. An alternative procedure which obviates the need for ²²³Ra is demonstrated for sediments by the assay of ²²⁴Ra and ²²⁸Th which occur naturally in sediments. In addition, a direct method for β-counting ²²⁸Ra–²²⁸Ac is proposed. Radium, polonium, thorium and uranium isotopes and ²¹⁰Pb are coprecipitated from sea water with aluminum phosphate carrier. The radium and lead-210 are coprecipitated with lead nitrate in sediment leachings. All radium procedures utilize identical chemical isolation and the cathodic electrodeposition of radium. Subsequently, the α-radiation emitted by ²²⁶Ra, ²²³Ra and ²²⁴Ra is determined by pulse-height analysis: the ²²⁸Ra-²²⁸Ac and ²¹⁰Pb-²¹⁰Bi are measured by low background anticoincidence β-counting techniques. This method was used for samples containing 10^-11–0.5 · 10^-12 g of ²²⁶Ra and 10^-13–10^-15 g of ²²⁸Ra and gave a precision of 3–6% and 5–10% respectively, even though radium levels an order of magnitude less can be measured. The ²²⁶Ra method is applicable to all environmental samples, whereas ²²⁸Ra determinations are limited to applications where the ${}^{228}\text{Ra}{}^{226}\text{Ra}$ activity ratio is greater than 0.1. This method is especially attractive for studies of parent-daughter disequilibria.     

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil

A sequential radiochemical procedure for isotopic analysis of uranium and thorium in soil has been developed. Analysis involves total dissolution of the samples to allow equilibration of the natural isotopes with added tracers, followed by radiochemical separation using anion exchange chromatography (BioRad AG 1–X8). Further separation and purification is performed employing solvent extraction techniques. Finally, the U and Th fractions are co-precipitated with lanthanum and cerium fluoride, respectively, and quantified by alpha-particle spectrometry. Overall chemical yields range from 60 to 90%. Under normal operating conditions and present counting set up, the minimum detectable concentration (MDC) is approximately 2 Bq/kg for soil samples. This is based on one gram aliquot of sample, 80% chemical yield, and 1000 minute counting with a detector having about 15% counting efficiency. The procedure has been successfully tested with Standard Reference Materials. Various soil samples were analyzed with high chemical yields and fine quality of alpha-spectra. Decontamination factor studies were performed to determine the extent of the carry over of²¹⁰Po,²²⁵Ac,²²⁶Ra, and²²⁹Th into U fraction and²¹⁰Po,²²⁵Ac,²²⁶Ra, and²³²U into Th fraction.     

Methodological advances for measuring low-level radium isotopes in seawater

A new approach for quantifying radium isotopes in seawater was developed in advance of the international GEOTRACES program, which has the goal of identifying processes and quantifying fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean. High-resolution water column samples were collected via a commercially available in situ pump modified to accept multiple filter media including a manganese-oxide (MnO₂) impregnated acrylic cartridge for extracting dissolved radionuclides from seawater. The modifications mitigated prefilter clogging and allowed for up to 1,800 L filtrations in 4 h of pumping. Different MnO₂ cartridge preparation methods were investigated to achieve maximum radium (Ra) extraction efficiency under high sample flow rates. Full-ocean depth profiles were measured for short-lived radium isotopes (²²³Ra and ²²⁴Ra) in shipboard laboratories using a delayed coincidence alpha scintillation counter (RaDeCC). Samples were reanalyzed 4 weeks and 2 months after collection for ²²⁸Th and ²²⁷Ac to correct for supported ²²⁴Ra and ²²³Ra, respectively. Finally, the cartridges were measured on a gamma-ray spectrometer for the long-lived radium isotopes (²²⁶Ra and ²²⁸Ra). Parallel 20 L samples at each pumping depth were collected from Niskin bottles and analyzed via alpha scintillation for ²²⁶Ra to determine radium extraction efficiencies for the cartridges. These modified methods will allow for increased sample throughput, and hence higher spatial resolution for radium isotopes in the ocean. Such resolution will greatly improve the determination of oceanic vertical and horizontal mixing rates over small and large scales, which in turn can be used to calculate fluxes of TEIs into the ocean.     

Calibration and optimization of alpha-beta separation procedures for determination of radium/radon in single- and two-phase liquid scintillation systems

Liquid scintillation alpha beta discrimination technique based on pulse shape analysis (PSA) was evaluated for determination of ²²⁶Ra and ²²²Rn in water samples. In view of the significance of calibration, for the reliable and precise determination of ²²⁶Ra and ²²²Rn concentrations in water samples, calibration procedures were standardized for single and two phase systems using Quantulus 1220 liquid scintillation counter. PSA optimization and efficiency calibrations were performed using ²²⁶Ra standard rather than conventionally used pure alpha and beta standards and substantiated by measuring the activity concentrations of ²²⁶Ra and ²²²Rn in the spiked water samples.