Determination of photon emission probability for the main gamma ray and half-life measurements of 64Cu

The National Institute of Standards and Technology (NIST) performed new standardization measurements for 64Cu. As part of this work the photon emission probability for the main gamma-ray line and the half-life were determined using several high-purity germanium (HPGe) detectors. Half-life determinations were also carried out with a NaI(Tl) well counter and two pressurized ionization chambers.

Production and characterization of a traceable NORM material and its use in proficiency testing of gamma-ray spectrometry laboratories

This paper outlines the process of characterizing a new NORM material for proficiency testing made of quartz sand with significantly elevated levels of ²²⁶Ra obtained from the backflush of a drinking water treatment facility. Samples of the fully characterized NORM material were sent to European laboratories concerned with radioactivity measurements and environmental monitoring by gamma-ray spectrometry for proficiency testing. The paper discusses the results, specific requirements, problems and solutions that were found during the characterization process and the proficiency test.

On homogeneity approximation in calibration of gamma-spectrometry assessment of bulk samples

The effect of the intrinsic inhomogeneity of a sample on the efficiency for the measurement of the sample by gamma-ray spectrometry is studied. The difference between the efficiency for the inhomogeneous sample and the efficiency for a sample made from the equivalent homogeneous matrix is evaluated.

Uncertainty of determination of 158Tb in the RBMK nuclear reactor waste

The activity of ¹⁵⁸Tb was measured in waste samples from the Ignalina NPP Unit I RBMK-1500 reactor using gamma-ray spectrometry. The origin of ¹⁵⁸Tb and the other observed gamma-ray emitters has been studied by using SCALE 6.1 modeling and comparing radionuclide ratios in the RBMK-1500 radioactive waste. The results of the calculation of the massic activity of gamma-ray emitters were used for interpretation of the total gamma-ray spectrum and the determination of ¹⁵⁸Tb massic activity uncertainty in the waste of RBMK-1500.

Standardization of 142Pr activity concentration

¹⁴²Pr (praseodymium-142), a potential radionuclide for brachytherapy, was produced after irradiating high purity natural Pr₂O₃ powder in a research reactor. The irradiated powder was then dissolved in acids and diluted for measurement. Several radioactivity measurement methods were used in the standardization of ¹⁴²Pr radionuclide. This work reports the results of standardization of ¹⁴²Pr with CIEMAT/NIST efficiency tracing method, gamma spectrometry and a calibrated ionization chamber. The activity measured from different standardization methods are compatible with each other within the uncertainty limits. The CIEMAT/NIST efficiency tracing method gives the lowest uncertainty and is a reliable method for the standardization of this radionuclide.

Development of separation techniques for analysis of Nb-94 in radwaste samples

A chemical separation technique for removing interfering gamma-ray radionuclides by combined precipitation of Nb pentoxide and anion exchange was proposed, thereby allowing detection of trace ⁹⁴Nb in low-level radwastes. The detection limit for ⁹⁴Nb was improved by a factor of 10-10³, and the scaling factor (⁹⁴Nb/⁶⁰Co) of the radwastes was estimated to be less than 10^-5. This technique can be used for low-level radwaste classification and power reactor decommissioning.

A gamma-ray spectrometry analysis software environment

At the JRC-Geel's RadioNuclide Metrology sector, a Monte Carlo code based on EGSnrc, and a general purpose calculation sheet implemented in Microsoft Excel^®, have been developed to make the quantitative gamma-ray spectrometry analysis of samples simpler and more robust. The further aim is that the software can be used by non-experts in gamma-ray spectrometry e.g. external researchers using JRC-Geel's facilities through the EUFRAT transnational access scheme. This paper presents the developed Monte Carlo software and the functionality included in the calculation sheet.

Systematic influences on the areas of peaks in gamma-ray spectra that have a large statistical uncertainty

A method is presented for calculating the expected number of counts in peaks that have a large relative peak-area uncertainty and appear in measured gamma-ray spectra. The method was applied to calculations of the correction factors for peaks occurring in the spectra of radon daughters. It was shown that the factors used for correcting the calculated peak areas to their expected values decrease with an increasing relative peak-area uncertainty. The accuracy of taking the systematic influence inducing the correction factors into account is given by the dispersion of the correction factors corresponding to specific peaks. It was shown that the highest accuracy is obtained in the peak analyses with the GammaVision and Gamma-W software.

A brief overview on radon measurements in drinking water

The aim of this paper is to present information about currently used standard and routine methods for radon analysis in drinking waters. An overview is given about the current situation and the performance of different measurement methods based on literature data. The following parameters are compared and discussed: initial sample volume and sample preparation, detection systems, minimum detectable activity, counting efficiency, interferences, measurement uncertainty, sample capacity and overall turnaround time. Moreover, the parametric levels for radon in drinking water from the different legislations and directives/guidelines on radon are presented.

Evidence for revision of the evaluated half-life of 207Bi

The National Institute of Standards and Technology (NIST) compared the measured full-energy peak efficiency obtained from a large set of sources to that of a ²⁰⁷Bi source obtained using three different half-life values. The values of the half-life used for this comparison are published in the Decay Data Evaluation Project (32.9 ± 1.4) years and the Evaluated Nuclear Structure Data File (31.55 ± 0.04) years, and in a recent NIST publication (31.20 ± 0.05) years (or (11395 ± 18) days).

Thirty years after Chernobyl: Long-term determination of 137Cs effective half-life in the lichen Stereocaulon vesuvianum

It has been widely shown that nuclear fallout includes substances, which accumulate in organisms such as crustaceans, fish, mushrooms and lichens, helping to evaluate the activity concentration of contaminants accumulated on a long time. In this context, radiocaesium deposited in soil following the Chernobyl accident on 26 April 1986 is known to have remained persistently available for plant uptake in many areas of Europe. Studies on the lichen Stereocaulon vesuvianum show the plant's high capacity to retain radionuclides from the substrate and the air. After the Chernobyl accident, starting from September 1986, at the Radioactivity Laboratory (LaRa) of the University of Naples Federico II, four monitoring campaigns to evaluate the activity concentration of four isotopes of the two elements caesium and ruthenium (¹³⁴Cs, ¹³⁷Cs, ¹⁰³Ru and ¹⁰⁶Ru) were carried out until 1999. This study allowed the effective half-life of ¹³⁴Cs and ¹³⁷Cs to be estimated. Twenty-eight years after the accident, in December 2014, a further sampling was carried out; only ¹³⁷Cs was revealed beyond the detection limits, measuring activity concentrations ranging from 20 to 40 Bq/kg, while the other radionuclides were no longer observed due to their shorter half-life. The last sampling allowed more precise determination of the effective half-life of ¹³⁷Cs (6.2 ± 0.1 year), due to the larger dataset on a large time period.

Variation of natural radionuclides in non-ferrous fayalite slags during a one-month production period

The European Basic Safety Standards (EU-BSS) describes a set of NORM (Naturally Occurring Radioactive Material)-processing industries which produce residues known to be possibly enriched in NORs (Naturally Occurring Radionuclides). These residues can be used as a component in building materials aimed for public usage. The industrial processes, in which the residues are produced, are often complex and total monitoring can be challenging especially when the origin of the used raw materials varies. In this study the NORs present in non-ferrous fayalite slags of a secondary smelter facility, a NORM-processing industry according to the EU-BSS, were monitored daily during a one-month production period. In addition flue dust samples and feedstock samples, known to contain elevated levels of NORs, of the same period were measured. The survey involved the gamma-ray spectrometric analysis of the decay products from the ²³⁸U and ²³²Th decay chains, ²³⁵U and ⁴⁰K using HPGe detectors. Secular equilibrium was observed for the slags, flue dust and feedstock samples in the ²³²Th decay chain, in contrast to the ²³⁸U decay chain. During the month in question the ratios of maximum over minimum activity concentration were 3.1 ± 0.5 for ⁴⁰K, 4 ± 1 for ²³⁸U, 6 ± 1 for ²²⁶Ra, 13 ± 7 for ²¹⁰Pb, 4.5 ± 0.6 for ²²⁸Ra and 4.7 ± 0.7 for ²²⁸Th for the slags. Even with the activity concentration of the feedstock material ranging up to 2.1 ± 0.3 kBq/kg for ²³⁸U, 1.6 ± 0.2 kBq for ²²⁶Ra, 22 ± 7 kBq/kg for ²¹⁰Pb, 2.1 ± 0.2 kBq/kg for ²²⁸Ra and 2.0 ± 0.4 kBq/kg for ²²⁸Th, none of the slag samples exceeded the exemption/clearance levels of the EU-BSS and RP-122 part II, which can respectively provide guidance under equilibrium and in absence of equilibrium. As each NORM-processing industry has its own complexity and variability, the observed variations point out that one should approach one-time measurements or low frequency monitoring methods cautiously. Low frequency measurements should be optimised depending on the discharge of the batches. A follow up of the industrial process and its output can provide important insights to assure a limited public exposure upon application of these industrial residues. Finally a comparison is made with reported data on other metallurgical slags and the use of the slags in building materials is evaluated using the Activity Concentration Index (ACI) proposed by the EU-BSS.

The re-evaluation of the 234mPa's 1001.03 keV gamma emission absolute intensity for the precise assessment of 238U

In this study the commonly used f-value for the 1001.03 keV (0.835 ± 0.004%) energy transition of the ^234mPa was re-evaluated due to an obvious consistent overestimation of the ²³⁸U activity concentration. Different calibration protocols, samples' matrices and geometries, and gamma-ray spectrometers were exploited in order to assure the accuracy of the derived data. An average positive relative bias of about 24% from the currently used f-value was estimating leading to newly adopted f-value of 1.037 ± 0.052%. This newly suggested f-value will lead to an improvement in the accurate assessment process of the ²³⁸U using gamma-ray spectrometry in both environmental and nuclear safeguard fields.

Environmental radioactivity study of Austrian and Bavarian forest ecosystems: Long-term behaviour of contamination of soil, vegetation and wild boar and its radioecological coherences

¹³⁷Cs and ⁴⁰K in soil, vegetation and flesh of wild boar samples from Austrian and Bavarian regions were investigated by gamma-ray spectrometry and ⁹⁰Sr in bones of wild boar with Liquid Scintillation Counting (LSC) after radiochemical separation. The soil core profiles revealed that 70-97% of the soil caesium content is still accumulated in the 0-10cm soil depth. From all vegetation samples the mushrooms, particularly the bay boletus showed the highest ¹³⁷Cs contamination. The activity concentration of ¹³⁷Cs in muscle tissue of boar ranged from 14.9±1.5Bq/kg (Bavaria) to 4711±377Bq/kg (Lower Austria). In the bones of wild boars, ⁹⁰Sr activity concentration ranged from 1.4±0.2Bq/kg (Bavaria) to 70.3±10.5Bq/kg (Upper Austria).

Determination of the self-attenuation based on the sample composition in gamma-ray spectrometry of 210Pb: requirements for the scope of chemical analyses

In the presented paper analysis of sensitivity of self-attenuation correction C_s to the accuracy of chemical composition analysis is presented. The analyses were done by means of Monte Carlo simulation for cylindrical samples and for four sample materials: peat, water, ash and soil. For each of these materials the major elements were selected whose determination in the analysed material is necessary. For the remaining elements threshold levels of their concentration were determined-if expected element concentration in a sample exceeds this value, its determination is indispensable, assuming the accuracy of C_s determination at 3 %.

Application of mathematical calibrations in measurements of gamma emitting radionuclides in honey samples and borosilicate filters

Mathematical efficiency calibrations for the specific matrices such as honey and borosilicate filters are performed. Their reliability is experimentally tested. The influence of the choice of the matrix composition in the mathematical calibration on the results is investigated. After the verification of the mathematical models, the results for activity concentrations in the test samples are presented.

Efficiency computation for gamma-ray spectrometry assessment of samples with intrinsic inhomogeneity

The full energy peak efficiency for inhomogeneous samples, comprising a number of components with different activity and matrix is evaluated by Monte Carlo simulation. The distribution of the values of the efficiency due to the effects of inhomogeneity is constructed. In the particular case when one of the components is a highly active and highly attenuating medium, then the efficiency and its uncertainty at low energies is sensitive to the properties of this component, including the dimensions of the grains.

Leda: A gamma-gamma coincidence spectrometer for the measurement of environment samples

This paper presents a new gamma-gamma coincidence spectrometer to measure the radioactivity in environmental samples. This system, called Leda, is made of 2 HPGe and 1 NaI(Tl). The different analysis channels (single, in coincidence or in anti-coincidence) possible thanks to the digital electronics are described. Results obtained with environmental samples are shown. Despite its low efficiency, this method improves the detection limits for all emitters due to its very low background, and thus decreases the counting time.

A low-energy set-up for gamma-ray spectrometry of NORM tailored to the needs of a secondary smelting facility

A measurement station dedicated for quantitative radiological characterisation of naturally occurring radionuclides in a metallurgical company and based on gamma-ray spectrometry was developed. The station is intended for performing quality control of final non-ferrous metal products and for radiological checks of incoming materials. A low-background point-contact HPGe-detector was used and the signal was split in two branches to enable collecting simultaneously spectra with high amplification (for gamma-ray energies below 250keV) and low amplification.

Determination of the measurement threshold in gamma-ray spectrometry

In gamma-ray spectrometry the measurement threshold describes the lover boundary of the interval of peak areas originating in the response of the spectrometer to gamma-rays from the sample measured. In this sense it presents a generalization of the net indication corresponding to the decision threshold, which is the measurement threshold at the quantity value zero for a predetermined probability for making errors of the first kind. Measurement thresholds were determined for peaks appearing in the spectra of radon daughters ²¹⁴Pb and ²¹⁴Bi by measuring the spectrum 35 times under repeatable conditions. For the calculation of the measurement threshold the probability for detection of the peaks and the mean relative uncertainty of the peak area were used. The relative measurement thresholds, the ratios between the measurement threshold and the mean peak area uncertainty, were determined for 54 peaks where the probability for detection varied between some percent and about 95% and the relative peak area uncertainty between 30% and 80%. The relative measurement thresholds vary considerably from peak to peak, although the nominal value of the sensitivity parameter defining the sensitivity for locating peaks was equal for all peaks. At the value of the sensitivity parameter used, the peak analysis does not locate peaks corresponding to the decision threshold with the probability in excess of 50%. This implies that peaks in the spectrum may not be located, although the true value of the measurand exceeds the decision threshold.

Study of particular problems appearing in NORM samples and recommendations for best practice gamma-ray spectrometry

In this paper spectral interference effects for selected gamma-emitting radionuclides of the natural decay series and ⁴⁰K in selected NORM samples are studied. Recommendations for the choice of γ-lines and the consideration of possible spectral interferences are provided. Special attention is given to the radon tightness of the sample containers. A simple and sensitive method for the estimation of the ²²²Rn leakage of sample containers is introduced. The applied polystyrene sample containers show ²²²Rn leakages lower than 1%.

Mapping natural radioactivity of soils in the eastern Canary Islands

The Canary Islands archipielago (Spain) comprises seven main volcanic islands and several islets that form a chain extending for around 500 km across the eastern Atlantic, between latitudes 27°N and 30°N, with its eastern edge only 100 km from the NW African coast. The administrative province of Las Palmas comprises the three eastern Canary Islands (Lanzarote, Fuerteventura and Gran Canaria). An extensive study of terrestrial gamma dose rates in surface soils has been carried out to cover the entire territory of the province (4093 km²). The average outdoor gamma dose rate in air at 1 m above ground is 73 nGyh^-1 at Gran Canaria, 32 nGyh^-1 at Fuerteventura, and 25 nGyh^-1 at Lanzarote. To complete the radiological characterization of this volcanic area, 350 soil samples at 0-5 cm depth were collected to cover all the geologic typologies of the islands. These samples were measured using high resolution gamma spectrometry to determine the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K. The average values obtained were 25.2 Bq/kg, 28.9 Bq/kg, and 384.4 Bq/kg, respectively. Maps of terrestrial gamma activity, effective dose, and activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K for the region have been developed through the use of geostatistical interpolation techniques. These maps are in accord with the geology of the islands.

A second-generation low-background gamma-ray spectrometer

For the ultimate sensitivity in trace radiochemical analysis, the radiation detector must have high efficiency and low background. A low-background gamma-ray spectrometer in regular use at NIST for over twenty years is being supplemented by a new system, improved in several ways. The new detector is much larger, a shield of iron reduces cosmic neutron background compared with lead, large plastic scintillators reduce the muon continuum background, and a digital data acquisition system gives new opportunities for optimization.

Characterization of the natural radioactivity of the first deep geothermal doublet in Flanders, Belgium

Deep geothermal energy is a local energy resource that is based on the heat generated by the Earth. As the heat is continuously regenerated, geothermal exploitation can be considered as a renewable and, depending on the techniques used, a sustainable energy production system. In September 2015, the Flemish Institute for Technological Research (VITO) started drilling an exploration well targeting a hot water reservoir at a depth of about 3km on the Balmatt site near Mol. Geothermal hot water contains naturally occurring gases, chemicals and radionuclides at variable concentrations. The actual concentrations and potentially related hazards strongly depend on local geological and hydrogeological conditions. This paper summarizes the radiological characterization of several rock samples obtained from different depths during the drilling, the formation water, the salt and the sediment fraction. The results of our analyses show low values for the activity concentration for uranium and thorium in the formation water and in the precipitate/sediment fraction. Also, the activity concentrations of ²¹⁰Pb and ²¹⁰Po are low in these samples and the activity concentration of ²²⁶Ra is dominant. From the analysis of the rock samples, it was found that the layer above the reservoir has a higher uranium and thorium concentration than the layer of the reservoir, which on the other hand contains more radium than the layer above it.

Detection limits should be a thing of the past in gamma-ray spectrometry in general as well as in neutron activation analysis

In gamma-ray spectrometry with high-resolution detectors, full-energy peaks are often to be detected by a peak-search algorithm, with a threshold for detection. Detection limits can be derived from this. Detection limits are often computed along with measured activities or concentrations. When an analyte is not detected, the detection limit remains as the only available information. This leads to inhomogeneous datasets that are difficult or impossible to process correctly without introducing artefacts or biases. Here, it is proposed to determine peak areas at predetermined energies. An unbiased result with its uncertainty always results, obviating the “detection limit” concept.

(60)Co in cast steel matrix: A European interlaboratory comparison for the characterisation of new activity standards for calibration of gamma-ray spectrometers in metallurgy

Two series of activity standards of (60)Co in cast steel matrix, developed for the calibration of gamma-ray spectrometry systems in the metallurgical sector, were characterised using a European interlaboratory comparison among twelve National Metrology Institutes and one international organisation. The first standard, consisting of 14 disc shaped samples, was cast from steel contaminated during production ("originally"), and the second, consisting of 15 similar discs, from artificially-contaminated ("spiked") steel. The reference activity concentrations of (60)Co in the cast steel standards were (1.077±0.019) Bqg(-1) on 1 January 2013 12h00 UT and (1.483±0.022) Bqg(-1) on 1 June 2013 12h00 UT, respectively.

Computation of full energy peak efficiency for nuclear power plant radioactive plume using remote scintillation gamma-ray spectrometry

A method of full energy peak efficiency estimation in the space around scintillation detector, including the presence of a collimator, has been developed. It is based on a mathematical convolution of the experimental results with the following data extrapolation. The efficiency data showed the average uncertainty less than 10%. Software to calculate integral efficiency for nuclear power plant plume was elaborated. The paper also provides results of nuclear power plant plume height estimation by analysis of the spectral data.

Mapping the spatial distribution and activity of (226)Ra at legacy sites through Machine Learning interpretation of gamma-ray spectrometry data

Radium ((226)Ra) contamination derived from military, industrial, and pharmaceutical products can be found at a number of historical sites across the world posing a risk to human health. The analysis of spectral data derived using gamma-ray spectrometry can offer a powerful tool to rapidly estimate and map the activity, depth, and lateral distribution of (226)Ra contamination covering an extensive area. Subsequently, reliable risk assessments can be developed for individual sites in a fraction of the timeframe compared to traditional labour-intensive sampling techniques: for example soil coring. However, local heterogeneity of the natural background, statistical counting uncertainty, and non-linear source response are confounding problems associated with gamma-ray spectral analysis. This is particularly challenging, when attempting to deal with enhanced concentrations of a naturally occurring radionuclide such as (226)Ra. As a result, conventional surveys tend to attribute the highest activities to the largest total signal received by a detector (Gross counts): an assumption that tends to neglect higher activities at depth. To overcome these limitations, a methodology was developed making use of Monte Carlo simulations, Principal Component Analysis and Machine Learning based algorithms to derive depth and activity estimates for (226)Ra contamination. The approach was applied on spectra taken using two gamma-ray detectors (Lanthanum Bromide and Sodium Iodide), with the aim of identifying an optimised combination of detector and spectral processing routine. It was confirmed that, through a combination of Neural Networks and Lanthanum Bromide, the most accurate depth and activity estimates could be found. The advantage of the method was demonstrated by mapping depth and activity estimates at a case study site in Scotland. There the method identified significantly higher activity (<3 Bq g(-1)) occurring at depth (>0.4m), that conventional gross counting algorithms failed to identify. It was concluded that the method could easily be employed to identify areas of high activity potentially occurring at depth, prior to intrusive investigation using conventional sampling techniques.

Determination of X- and gamma-ray emission intensities in the decay of (131)I

The activity per unit mass of an iodine-131 solution was absolutely standardized by both the 4πβ-γ coincidence method and the 4πγ counting technique. The calibrated solution was used to prepare point sources after a preliminary deposit of AgNO3 to prevent the loss of volatile iodine. Relative and absolute photon emission intensities of 15 sgamma-rays and those of the two K X-rays of xenon were determined by gamma-ray spectrometry, with relative uncertainties of 0.8% for the three main emissions.

Mapping radon hazard areas using 238U measurements and geological units: a study in a high background radiation city of China

In order to identify radon-prone areas and evaluate radon risk level, a soil gas radon survey combined with gamma-ray spectrometry measurements was carried out in Shenzhen City, south China. Meanwhile, the statistical analysis was applied to evaluate the distribution of measured results. This paper presents the methodology of the radon risk assessment. A radon risk map was accomplished based on a combination of soil gas radon concentration (RC), soil air permeability (Perm.) and uranium (²³⁸U) concentration. The results showed that the distribution of soil gas RC and radon-prone areas were closely related to geologic distribution of uranium (²³⁸U) and local lithology.

Determination of absolute photon emission intensities of (210)Pb

Photon emission intensities of (210)Pb have been determined using sources prepared from a standard solution, whose activity was measured by liquid scintillation counting. The absolute γ-ray and X-ray emission intensity was measured by conventional γ-ray spectrometry. Complementary measurements of the L X-ray spectrum were performed using a cryogenic detector, characterized by very high energy resolution and constant detection efficiency. As a result, precise emission intensities of the individual X-ray lines were obtained taking into account the presence of satellite lines.

A preliminary evaluation of naturally occurring radioactivity concentration levels across the State of Kuwait

An evaluation of naturally occurring radioactive materials has been undertaken as part of a systematic study to provide a surface radiological map of the State of Kuwait. Soil samples were collected from twelve locations across Kuwait and analysed using high-resolution gamma-ray spectrometry. The (226)Ra and (235)U specific activity concentrations have been determined and used to estimate the (235)U/(238)U isotopic ratios which are found to be comparable to that expected for naturally occurring uranium material.

Determination of the (241)Am activity in real contaminated slag

One of the main tasks of the EMRP IND04 MetroMetal project "Ionising Radiation Metrology for the Metallurgical Industry" was to develop sets of reference sources in various matrices such as cast steel, slag and fume dust for the calibration of the gamma spectrometric detector prototypes developed in the frame of the project. This work is focused on the characterisation of real contaminated slag material with (241)Am using the transmission measurements in combination with Monte-Carlo simulations. The method and the results are presented and discussed.

Assessing sample attenuation parameters for use in low-energy efficiency transfer in gamma-ray spectrometry

We present a numerical fitting method for transmission data that outputs an equivalent sample composition. This output is used as input to a generalised efficiency transfer model based on the EFFTRAN software integrated in a LIMS. The procedural concept allows choosing between efficiency transfer with a predefined sample composition or with an experimentally determined composition based on a transmission measurement. The method can be used for simultaneous quantification of low-energy gamma emitters like (210)Pb, (241)Am, (234)Th in typical environmental samples.

Low level measurement of (60)Co by gamma ray spectrometry using γ-γ coincidence

This paper presents the latest development of the laboratory to measure the natural and artificial massic activities in environmental samples. The measurement method of coincident emitters by gamma-gamma coincidence using an anti-Compton device and its digital electronics is described. Results obtained with environmental samples are shown. Despite its low efficiency, this method decreases detection limits of (60)Co for certain samples compared to conventional gamma-ray spectrometry due to its very low background.

Assessment of measurement result uncertainty in determination of (210)Pb with the focus on matrix composition effect in gamma-ray spectrometry

Reference materials were used to assess measurement result uncertainty in determination of (210)Pb by gamma-ray spectrometry, liquid scintillation counting, or indirectly by alpha-particle spectrometry, using its daughter (210)Po in radioactive equilibrium. Combined standard uncertainties of (210)Pb massic activities obtained by liquid scintillation counting are in the range 2-12%, depending on matrices and massic activity values. They are in the range 1-3% for the measurement of its daughter (210)Po using alpha-particle spectrometry. Three approaches (direct computation of counting efficiency and efficiency transfer approaches based on the computation and, respectively, experimental determination of the efficiency transfer factors) were applied for the evaluation of (210)Pb using gamma-ray spectrometry. Combined standard uncertainties of gamma-ray spectrometry results were found in the range 2-17%. The effect of matrix composition on self-attenuation was investigated and a detailed assessment of uncertainty components was performed.

Characterisation of the IAEA-375 Soil Reference Material for radioactivity

The Joint Research Centre Institute for Reference Materials and Measurements (JRC-IRMM) participated in a research project initiated by the International Atomic Energy Agency (IAEA) to upgrade some of its existing reference materials (RMs). The aim of the work described in this article was to determine the activity concentration of a series of radionuclides in the IAEA-375 soil RM with values traceable to the SI units. The radionuclides (40)K, (134)Cs, (137)Cs, (212)Pb, (212)Bi, (214)Pb and (214)Bi were measured by γ-ray spectrometry after drying the sample and placing it in a suitable container. The (90)Sr was assessed by liquid scintillation counting after dissolution of the soil by wet digestion and chemical separation of Sr by extraction chromatography. This soil RM was used later as basis for the 2010 EC Interlaboratory Comparison on Radionuclides in Soil.

Equivalence of computer codes for calculation of coincidence summing correction factors - Part II

The aim of this study was to check for equivalence of computer codes that are capable of performing calculations of true coincidence summing (TCS) correction factors. All calculations were performed for a set of well-defined detector parameters, sample parameters and decay scheme data. The studied geometry was a point source of (133)Ba positioned directly on the detector window of a low-energy (n-type) detector. Good agreement was established between the TCS correction factors computed by the different codes.

Comparisons organized by Ionizing Radiation Metrology Laboratory of FTMC, Lithuania

The newly established Ionizing Radiation Metrology Laboratory of the National Metrology Institute (FTMC) in Lithuania organized four comparisons in the field of low-level radioactivity measurements in water. For gamma-ray emitters, the activity concentration in the samples was in the range 1-25Bq/kg, while for tritium it was around 2Bq/g. The assigned values of all comparisons were traceable to the primary standards of the Czech Metrology Institute (CMI).

A simple methodology for characterization of germanium coaxial detectors by using Monte Carlo simulation and evolutionary algorithms

The determination in a sample of the activity concentration of a specific radionuclide by gamma spectrometry needs to know the full energy peak efficiency (FEPE) for the energy of interest. The difficulties related to the experimental calibration make it advisable to have alternative methods for FEPE determination, such as the simulation of the transport of photons in the crystal by the Monte Carlo method, which requires an accurate knowledge of the characteristics and geometry of the detector. The characterization process is mainly carried out by Canberra Industries Inc. using proprietary techniques and methodologies developed by that company. It is a costly procedure (due to shipping and to the cost of the process itself) and for some research laboratories an alternative in situ procedure can be very useful. The main goal of this paper is to find an alternative to this costly characterization process, by establishing a method for optimizing the parameters of characterizing the detector, through a computational procedure which could be reproduced at a standard research lab. This method consists in the determination of the detector geometric parameters by using Monte Carlo simulation in parallel with an optimization process, based on evolutionary algorithms, starting from a set of reference FEPEs determined experimentally or computationally. The proposed method has proven to be effective and simple to implement. It provides a set of characterization parameters which it has been successfully validated for different source-detector geometries, and also for a wide range of environmental samples and certified materials.

Monte Carlo calculations of the HPGe detector efficiency for radioactivity measurement of large volume environmental samples

A fully detailed Monte Carlo geometrical model of a High Purity Germanium detector with a (152)Eu source, packed in Marinelli beaker, was developed for routine analysis of large volume environmental samples. Then, the model parameters, in particular, the dead layer thickness were adjusted thanks to a specific irradiation configuration together with a fine-tuning procedure. Thereafter, the calculated efficiencies were compared to the measured ones for standard samples containing (152)Eu source filled in both grass and resin matrices packed in Marinelli beaker. From this comparison, a good agreement between experiment and Monte Carlo calculation results was obtained highlighting thereby the consistency of the geometrical computational model proposed in this work. Finally, the computational model was applied successfully to determine the (137)Cs distribution in soil matrix. From this application, instructive results were achieved highlighting, in particular, the erosion and accumulation zone of the studied site.

Determination of photon emission probabilities for the main gamma-rays of ²²³Ra in equilibrium with its progeny

The currently published (223)Ra gamma-ray emission probabilities display a wide variation in the values depending on the source of the data. The National Institute of Standards and Technology performed activity measurements on a (223)Ra solution that was used to prepare several sources that were used to determine the photon emission probabilities for the main gamma-rays of (223)Ra in equilibrium with its progeny. Several high purity germanium (HPGe) detectors were used to perform the gamma-ray spectrometry measurements.

Determining the radon exhalation rate from a gold mine tailings dump by measuring the gamma radiation

The mining activities taking place in Gauteng province, South Africa have caused millions of tons of rocks to be taken from underground to be milled and processed to extract gold. The uranium bearing tailings are placed in an estimated 250 dumps covering a total area of about 7000 ha. These tailings dumps contain considerable amounts of radium and have therefore been identified as large sources of radon. The size of these dumps make traditional radon exhalation measurements time consuming and it is difficult to get representative measurements for the whole dump. In this work radon exhalation measurements from the non-operational Kloof mine dump have been performed by measuring the gamma radiation from the dump fairly accurately over an area of more than 1 km(2). Radon exhalation from the mine dump have been inferred from this by laboratory-based and in-situ gamma measurements. Thirty four soil samples were collected at depths of 30 cm and 50 cm. The weighted average activity concentrations in the soil samples were 308 ± 7 Bq kg(-1), 255 ± 5 Bq kg(-1) and 18 ± 1 Bq kg(-1) for (238)U, (40)K and (232)Th, respectively. The MEDUSA (Multi-Element Detector for Underwater Sediment Activity) γ-ray detection system was used for field measurements. The radium concentrations were then used with soil parameters to obtain the radon flux using different approaches such as the IAEA (International Atomic Energy Agency) formula. Another technique the MEDUSA Laboratory Technique (MELT) was developed to map radon exhalation based on (1) recognising that radon exhalation does not affect (40)K and (232)Th activity concentrations and (2) that the ratio of the activity concentration of the field (MEDUSA) to the laboratory (HPGe) for (238)U and (40)K or (238)U and (232)Th will give a measure of the radon exhalation at a particular location in the dump. The average, normalised radon flux was found to be 0.12 ± 0.02 Bq m(-2) s(-1) for the mine dump.

Attenuation correction for the collimated gamma ray assay of cylindrical samples

The Hybrid Monte Carlo (HMC) method developed earlier for attenuation correction of non-collimated samples [Agarwal et al., 2008, Nucl. Instrum. Methods A 597, 198], has been extended to the segmented gamma ray assay of cylindrical samples. The method has been validated both experimentally and theoretically. For experimental validation, the results of HMC calculation have been compared with the experimentally obtained attenuation correction factors. The HMC attenuation correction factors have also been compared with the results obtained from literature available near-field and far-field formulae at two sample-to-detector distances (10.3cm and 20.4cm). The method has been found to be valid at all sample-to-detector distances over a wide range of transmittance. On the other hand, the literature available near-field and far-field formulae have been found to work over a limited range of sample-to detector distances and transmittances. The HMC method has been further extended to circular collimated geometries where analytical formula for attenuation correction does not exist.

Detailed deposition density maps constructed by large-scale soil sampling for gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident

Soil deposition density maps of gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant (NPP) accident were constructed on the basis of results from large-scale soil sampling. In total 10,915 soil samples were collected at 2168 locations. Gamma rays emitted from the samples were measured by Ge detectors and analyzed using a reliable unified method. The determined radioactivity was corrected to that of June 14, 2011 by considering the intrinsic decay constant of each nuclide. Finally the deposition maps were created for (134)Cs, (137)Cs, (131)I, (129m)Te and (110m)Ag. The radioactivity ratio of (134)Cs-(137)Cs was almost constant at 0.91 regardless of the locations of soil sampling. The radioactivity ratios of (131)I and (129m)Te-(137)Cs were relatively high in the regions south of the Fukushima NPP site. Effective doses for 50 y after the accident were evaluated for external and inhalation exposures due to the observed radioactive nuclides. The radiation doses from radioactive cesium were found to be much higher than those from the other radioactive nuclides.

Determination of (238)U, (232)Th and (40)K activity concentrations in riverbank soil along the Chao Phraya river basin in Thailand

The activity concentrations of (238)U, (232)Th and (40)K in riverbank soil along the Chao Phraya river basin was determined through gamma-ray spectrometry measurements made using a hyper-pure germanium detector in a low background configuration. The ranges of activity concentrations of (238)U, (232)Th and (40)K were found to be 13.9 ↔ 76.8, 12.9 ↔ 142.9 and 178.4 ↔ 810.7 Bq kg(-1), respectively. The anthropogenic radionuclide, (137)Cs, was not observed in statistically significant amounts above the background level in the current study. The absorbed gamma dose rate in air at 1 m above the ground surface, the outdoor annual effective dose equivalent, the values of the radium equivalent activity and the external hazard index associated with all the soil samples in the present work were evaluated. The results indicate that the radiation hazard from primordial radionuclides in all soil samples from the area studied in this current work is not significant.

Analysis of (7)Be behaviour in the air by using a multilayer perceptron neural network

A multilayer perceptron artificial neural network (ANN) model for the prediction of the (7)Be behaviour in the air as the function of meteorological parameters was developed. The model was optimized and tested using (7)Be activity concentrations obtained by standard gamma-ray spectrometric analysis of air samples collected in Belgrade (Serbia) during 2009-2011 and meteorological data for the same period. Good correlation (r = 0.91) between experimental values of (7)Be activity concentrations and those predicted by ANN was obtained. The good performance of the model in prediction of (7)Be activity concentrations could provide basis for construction of models which would forecast behaviour of other airborne radionuclides.

Correction to the recommended γ-ray emission intensity of the 255.13 keV photons in the decay of (113)Sn

The authors provide corrected measured values of the relative γ-ray emission intensity of the 255.13keV photons from the decay of (113)Sn. Consequently, new recommended values of the evaluated relative and absolute γ-ray emission intensity of the 255.13keV photons following the decay of (113)Sn are proposed.

Efficiency calibration of BEGe and extended range detectors

Any approach to efficiency calibration of HPGe detectors sensitive to low-energy gamma-rays and X-rays has to deal with true coincidence summing. We developed a method based on the integration of the EFFTRAN code into the commercial Genie2K™ gamma-ray spectrometry software. EFFTRAN's role is to compute true coincidence summing corrections and to obtain satisfactory results for detectors sensitive to X-rays. EFFTRAN had to be upgraded to include a full simulation of the emission of X-rays. In this manner, efficiency calibrations were successfully set up for BeGe and XtRa detectors.

Installation and performance testing of an XtRa-NaI(Tl) Compton Suppression System at the NED-NTUA

This paper presents the Compton Suppression System, recently installed at the Nuclear Engineering Department of NTUA. The system consists of an XtRa Ge detector coupled with a NaI(Tl) guard detector. The electronic set-up allows for the simultaneous collection of both the suppressed and the unsuppressed spectra. System performance is investigated using certified point and volume sources. Parameters such as Peak Suppression Factors, peak-to-Compton ratios and minimum detectable activity for specific radionuclides are determined.