Application of low energy gamma-spectrometry in rapid actinide analysis for emergency preparedness

For preparedness purposes, a fast and reliable method is essential to quickly assess radioactive fallout in the environment. The rapid determination of certain nuclides such as alpha-emitting actinides is necessary to make initial environmental and agricultural advisories. Therefore, a method using a preconcentration resin and low energy gamma-spectrometry was developed to a fast determination of certain nuclides in soil samples. The preconcentration resin allows samples to be partially purified and then directly measured by gamma-spectrometry without further extraction or separation. The initial gamma-measurement provides fast and accurate determination of certain nuclides such as ²⁴¹Am and ²³⁵U which are normally analyzed by alpha-spectrometry, but require additional time-consuming purification and separation steps. After gamma-spectrometry, the sample may be further processed and analyzed by traditional methods to determine actinides or other nuclides more precisely.     

Time sequence determination of parent–daughter radionuclides using gamma-spectrometry

The acquisition of time-stamped list data provides additional information useful to gamma-spectrometry analysis. A novel technique is described that uses non-linear least-squares fitting and the Levenberg–Marquardt algorithm to simultaneously determine parent-daughter atoms from time sequence measurements of only the daughter radionuclide. This has been demonstrated for the radioactive decay of short-lived radon progeny (²¹⁴Pb/²¹⁴Bi, ²¹²Pb/²¹²Bi) described using the Bateman first-order differential equation. The calculated atoms are in excellent agreement with measured atoms, with a difference of 1.3–4.8% for parent atoms and 2.4–10.4% for daughter atoms. Measurements are also reported with reduced uncertainty. The technique has potential to redefine gamma-spectrometry analysis.

     

The investigations on K and L X-ray fluorescence parameters of gold compounds

The study aimed to determine the chemical effects on the K and L X-ray intensity ratios and the K and L X-ray production cross sections for gold compounds. The K shell fluorescence yields and L shell average yields were also investigated. The samples were excited by 59.5 keV γ-rays from an ²⁴¹Am annular radioactive source and 123.6 keV γ-rays from a ⁵⁷Co annular radioactive source. K and L X-rays emitted from samples were counted by an Ultra-LEGe detector with a resolution of 0.150 keV at 5.9 keV. The experimental values were compared with theoretical, the semi-empirical and other experimental values.     

Determination of 210Pb in environmental samples

Summary Measurement of ²¹⁰Pb has gained a highly scientific attention due to its wide range of environmental applications. The most commonly used analytical techniques: gamma-spectrometry, beta-counting and alpha-spectrometry were used to measure environmental samples (geological, soil, sediment). Our paper is aiming at comparing the capabilities and limits of application of these three different analytical techniques for ²¹⁰Pb measurement in various environmental samples. In addition, analytical data of ²¹⁰Pb measurements with the three different techniques (gamma-spectrometry, beta-counting and alpha-spectrometry) are discussed to highlight the degree of comparability and the most probable sources of discrepancies and errors. Based on the demanded investigation, one analytical technique will be chosen for routine analysis, while the other techniques, if they are available, could be used for analytical quality assurance measures. It was essential to compare the analytical efficacy of each technique, which differ concerning the detection limit (MDA), sensitivity, analytical effort, the duration of analysis and waiting time before analysis.     

Recent developments in radiometric and mass spectrometry methods for marine radioactivity measurements

The most important recent developments in radiometric techniques have been the operation of high efficiency HPGe detectors with anticosmic or antiCompton shielding often placed underground, ship-board measurements of ²³⁴Th using gamma-spectrometry or beta-counting and underwater gamma-spectrometry. In mass spectrometry techniques, the availability of high resolution ICP-MS and applications of AMS for the analysis of long-lived radionuclides have opened doors for investigations which previously required too large samples, or were not possible because of lack of sensitivity. These developments are illustrated by several examples of marine radioactivity studies, which include contaminated sites (e.g., Fangataufa Atoll) and open ocean studies (e.g., the Atlantic Ocean) as well as analyses of IAEA reference materials. A comparison of Pu results obtained by alpha-spectrometry, ICP-MS and AMS has shown that a reasonably good agreement has been obtained between all three methods.     

Simultaneous determination of 226Ra and 238U in soil and environmental materials by gamma-spectrometry in the absence of radium progeny equilibrium

The determination of ²²⁶Ra and ²³⁸U in environmental samples by gamma-spectrometry is most often carried out by hermetic sealing of the sample in a suitable container, waiting until secular equilibrium that has been established in the ²³⁸U decay chain below ²²⁶Ra and counting of the high intensity emissions of ²¹⁴Pb and ²¹⁴Bi. The 186 keV multiplet can then be corrected to provide a measure of ²³⁵U and hence, ²³⁸U. The work presented in this paper involves a critical examination of the analysis of ²³⁸U and ²²⁶Ra in environmental materials without secular equilibrium established between ²¹⁴Pb, ²¹⁴Bi and their progenitor. Results indicate that the correction of the 186 keV doublet via ²³⁴Th determination is possible, even for low-level samples but careful consideration of both experimental conditions and the composition of the sample matrix is required. This revised version was published online in July 2006 with corrections to the Cover Date.     

Natural radioactivity in soils and rocks within the Greater Accra Region of Ghana

Natural radioactivity in soil and rock samples from different geologicalstructures in selected locations within the Greater Accra Region of Ghanahas been studied using gamma-spectrometry. Results indicated that the majorcontribution to terrestrial background radiation is the natural radioactiveseries notably ⁴⁰K, ²³⁸U and ²³²Th. Estimatedexposure rate at 1 m above the soil surface ranged from 0.9 to 20.6 µR/hin soils and 0.6 to 17.8 µR/h in rocks. Granitic rocks at Dodowa containhigher levels of the naturally occurring radioactive elements. The relativelylow concentration around the Shai Hills may be due to the predominance ofsand.     

Using Monte Carlo methods to estimate efficiencies of gamma-ray emitters with complex geometries

In the event of a radioactive disaster, one of the biggest tasks is to estimate the radiation dosage received by people to determine the actions of emergency response teams. The first and the most rapid screening method of internally contaminated people in case of an emergency response is to perform in-vivo measurements for gamma-emitters. Development of virtual gamma-ray calibration techniques will be critical for emergency invivo measurements because there are inadequate numbers of phantom types to approximate all body shapes and sizes. The purpose of this project was to find a reliable way to estimate the efficiency of gamma-systems using Monte Carlo computations, and to validate that efficiency by making measurements of a standard geometry. Two geometries, a 5-ml ampoule and a Bottle Manikin Absorption (BOMAB) phantom head, spiked with ⁶⁷Ga were used as standard geometries. The radioactive objects are measured at a number of distances from a high purity germanium (HPGe) detector, and the experimental efficiency for our gamma-spectrometry system is determined. The same set of experiments was then modeled using the Monte Carlo N-Particle Transport Code (MCNP). The conclusion of this project is that computationally derived detector efficiency calibrations can be comparable to those derived experimentally from physical standards.     

Uranium and plutonium containing particles in a sea sediment sample from Thule, Greenland

Particles composed of radioactive materials and probably originating from US nuclear weapons were identified in sea sediment samples collected from Thule, Greenland, in 1997. The weapons were destroyed close to the Thule Air Base in 1968 in an aeroplane crash, which dispersed radioactive materials in the environment. The presence of particulate radioactive materials in the sediment samples was revealed by combining gamma-spectrometry and autoradiography. Isolation and separation of a radioactive particle from a bulk sample were performed using autoradiography, phosphor plate imaging and scanning electron microscopy. Using X-ray microanalysis as well as alpha and beta activity analysis, U and weapons-grade Pu were detected in the granular, brittle particle.     

An accurate method for the determination of <Superscript>226</Superscript>Ra activity concentrations in soil

A quantitative method to determine the activity concentration of ²²⁶Ra in soil samples was established using high performance environmental gamma-ray spectrometry. In this method, a semi-empirical calibration procedure was developed for full energy peak efficiency calculation utilizing the elemental composition of the soil sample. Aatami software was used to deconvolute the ²³⁵U and ²²⁶Ra doublet at 185.7 keV and 186.2 keV, respectively, and to fit the baseline of the soil gamma-spectrum for the determination of ²²⁶Ra activity. The results indicated that the Aatami doublet deconvolution procedure provides a rapid and accurate analysis of a complicated spectrum in comparison with other cumbersome spectral interference correction methods. The study also compared the results with those obtained by radon progeny (²¹⁴Pb, or ²¹⁴Bi) measurements and found that the deconvolution method provided a more accurate ²²⁶Ra activity as it is independent of the error caused by radon diffusion. This error can be quite large since the amount of escaped radon gas through the sample container walls and sealing cannot be accurately quantified.     

Radioactive accumulation in alga samples from Romanian Black Sea coast

The natural and artificial radioactivity of the brown algaCystoseira barbata samples collected on the Romanian Black Sea coast in 1996 is reported. The results on¹³⁷Cs were obtained through gamma-spectrometry, on⁹⁰Sr by beta-counting of the⁹⁰Y oxalate precipitated after strontium separation, on²²⁶Ra by the emanation method, while the concentrations of U, Th, Pu and Am isotopes were obtained through radiochemical separations using tracers followed by alpha-spectrometry counting of the stainless steel discs after electrodeposition. These results add further evidence thatCystoseira barbata may be used as a bioindicator for radioactive contamination of the coastal waters.     

Chemical Effect on K Shell X-ray Fluorescence Parameters and Radiative Auger Ratios of Co,Ni, Cu,and Zn Complexes

The production cross-sections, intensity ratios, and radiative Auger intensity ratios of Co, Ni, Cu, and Zn elements in different complexes were measured. The chemical effects on the K shell fluorescence parameters and the radiative Auger intensity ratios of these elements were investigated and the changes in these parameters were interpreted according to the charge transfer process. The samples were excited by 59.5 keV γ-rays from a ²⁴¹Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV.     

A simple screening method for the determination of 230Th in soil and sediment samples by gamma-spectrometry

A simple and easy to perform method for the determination of ²³⁰ Th in soil and sediment samples using gamma-spectrometry is proposed and compared with the more usual procedure using alpha-particle spectrometry. The proposed method involves an efficiency calibration for the specific determination of this radionuclide instead of a complete calibration of the spectra. A single density parameter is introduced to correct the efficiencies obtained from the reference sources. The activities of ²³⁰ Th determined by gamma-spectrometry and alpha-particle spectrometry are compared. The minimum detectable activity values obtained are completely adequate for ²³⁰ Th determination in soil and sediment samples, in which ²³⁰ Th activities are usually fairly high. Thus, this procedure is intended as a very easy way to obtain the activity of this radionuclide in these types of samples, at least as a screening method before carrying out other more laborious procedures.     

Simultaneous determination of60Co,131I and137Cs in model radioactive waste water by reverse radiometric flow injection analysis with the aid of a multichannel analyzer

Reverse radiometric flow injection analysis was used for the simultaneous determination of⁶⁰Co,¹³¹I and¹³⁷Cs in model radioactive waste water. A NaI (Tl) scintillation detector coupled to a Canberra MCA was used for measuring the activity of¹³⁷Cs at 662 keV,⁶⁰Co at 1173 keV and 1332 keV, and¹³¹I at 364 keV.     

Epithermal neutron activation determination of uranium in environmental waters by neptunium-239 after preconcentration on activated carbon

A method for the analysis of uranium in natural waters based on preconcentration of uranium on activated carbon, irradiation with epithermal neutrons, and a high resolution gamma-spectrometry of²³⁹Np was developed. The chemical yield of uranium preconcentration is determined by treating a parallel sample to which a known uranium quantity is added. The lower limit of determination amounts to 1.4·10⁻⁸ g uranium per liter. The possible interfering in gamma-spectrometry of neptunium-239 was discussed too. The applicability of the proposed method is shown by the analysis of uranium in sea-, river-, geothermal-, drinking- and rain-water samples.     

Simplified evaluation of214Bi/238U activity ratios in fossil bones using non-destructive activation analysis

A simple and reliable method has been developed for the evaluation of radioactive disequilibrium state in fossil bones. The fossil bone samples were irradiated with an extremely low neutron fluence, together with a standard pitchblende prevailing the secular equilibrium among the uranium series. The²³⁹Np activity induced from²³⁸U in both samples were adjusted to be gamma-ray spectrometrically nearly equivalent to the naturally occurring radioactivities by controlling the neutron flux and cooling time. Using single gamma-ray spectrometry of the irradiated samples, the determination of²¹⁴Bi/²³⁸U in a fossil bone was carried out by comparing the photopeak ratios of²¹⁴Bi /609 keV/ and²³⁹Np /278 keV/ instead of²³⁸U with the same ratios from the pitchblende standard sample.     

Rapid determination of 237Np in soil samples by multi-collector inductively-coupled plasma mass spectrometry and gamma spectrometry

A radiochemical procedure is developed for the determination of ²³⁷Np in soil with multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) and gamma-spectrometry. ²³⁹Np (milked from ²⁴³Am) was used as an isotopic tracer for chemical yield determination. The neptunium in the soil is separated by thenoyl-trifluoracetone extraction from 1 M HNO₃ solution after reducing Np to Np(IV) with ferrous sulfamate, and then purified with Dowex 1 × 2 anion exchange resin. ²³⁹Np in the resulting solution is measured with gamma-spectrometry for chemical yield determination while the ²³⁷Np is measured with MC-ICP-MS. Measurement results for soil samples are presented together with those for two reference samples. By comparing the determined value with the reference value of the ²³⁷Np activity concentration, the feasibility of the procedure was validated.     

Neutron activation analysis of iodine in blood serum or other biological materials by substoichiometric precipitation of iodine as silver iodide

Several modifications are proposed of the established methods of iodine determination in serum. Prior to the actual analysis, the serum is lyophilized. This preliminary treatment permits the use of large samples. Through lyophilization human blood serum samples can easily be reduced to one-tenth of the original weight. Reduction is even more dramatic with materials from other than human origin. After irradiation the samples are subjected to chemical treatment in the presence of an iodine carrier and¹³¹I-labelled thyoxine. This procedure has been adopted for the determination of the iodine content and the chemical yield in one and the same radioactive measurement. The analysis technique itself consists of an open system Schöniger combustion. The open combustion allows the use of large samples; the gases evolved are absorbed upon their subsequent passage through potassium hydroxide and hydrochloric acid; the mineralization requires less than two minutes. After the addition of a substochiometric amount of silver nitrate, silver iodide is precipitated from an ammoniacal solution as a flat sample, which has been found ideally suited for high efficiency counting with a Ge(Li) detector. The spectrum gives evidence of an excellent decontamination from the³⁸Cl,⁸⁰Br and⁸²Br activities. The iodine content can be calculated from the ratio of the photopeak areas at 364.5 keV and 442.7 keV corresponding to¹³¹I and¹²⁸I, respectively. The chemical procedure requires a mere 15 min, and the recording of the γ-ray spectrum takes no longer than 30 min. The technique is not limited to serum only. It proved well suited for the analysis of many other types of biological material, e.g. human skin tissues.     

Automatic activation analysis

Automatic activation analysis (AAA) is rendered possible by a unique neutron activation analysis facility for short-lived isomeric transitions based on a fast rabbit system with sample changer and sample separation, and an adaptive digital gamma-spectrometer for very high counting rates of up to 10⁶ cps. The system is controlled by a computer program performing irradiation control, neutron flux monitoring, and gamma-spectrometry with real-time correction of counting losses, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic procedure. As spectrometry is done by means of hundreds of sequentially measured pairs of concurrently recorded loss-corrected and non-corrected spectra, concentrations are derived from an optimally weighted average of all individual occurrences in this sequence of spectra which also enable the separation of isomeric transitions with coinciding energies but different half-lives such as ^116m2In (162.4 keV, T _1/2 = 2.2 s) and ^77mSe (162.2 keV, T _1/2 = 17.4 s). To clear up repeatedly voiced misconceptions concerning the errors of loss-free counting our findings of 1978 and 1981 are reiterated, namely that the counting error of a peak in a corrected spectrum may be derived consistently from the error of the same peak in the respective non-corrected spectrum and from the error of weighting factors in the corresponding region of interest, according to the principle of propagation of errors. Experimental proof is provided for conditions of stationary as well as rapidly varying counting rates and spectral shapes. To the memory of Vincent P. Guinn.     

Gamma spectrometry of 234Th (238U) in environmental samples

Environmental samples from a wide-range of aquatic and soil deposits, mainly of Scandinavian origin, were analysed for 234Th (238U) using low-level gamma-spectrometry. The diversity of the samples, in terms of composition and ages, allowed a detailed evaluation of the analytical problems associated with gamma-ray spectrometry with focus on the reliability of the 234Th peaks for absolute determination of the 234Th activities. The X-ray contributions in the 93 keV peak were compared with the corresponding self-absorption corrected activities of the 63 keV peak. These X-ray contributions were, also, correlated with the 238U, 232Th, 235U, 40K and 137Cs activities of the samples. Despite the difficulties imposed by the self-absorption corrections, the 63 keV peak is still the best option. Large variability in the 93 keV peak interferences, due to X-rays from Th, exists in sediment and soil samples. Only in the case of young ombrotrophic peat samples was it possible to conclude that the 93 keV peak is free from X-ray contributions and can be as good as the 63 keV Monte-Carlo self-absorption corrected peak. X-ray contributions in the samples correlated with the 238U and 232Th activities, only, in closed environmental systems where a secular equilibrium with the daughters of the U/Th series can occur.