Absolute emission intensities of the gamma rays from the decay of 224Ra and 212Pb progenies and the half-life of the 212 Pb decay

Absolute gamma-ray emission intensities for 36 characteristic gamma rays from the decay of 224Ra, 212Pb, and their progeny were determined by measuring sources calibrated for activity by means of primary methods based on well-defined high-purity germanium (HPGe) detectors at both NIST and NPL. Results from the two laboratories agree with recent data evaluations, except for gamma rays with low emission intensities. The decay schemes have been re-balanced based on the new results. In addition, the half-life for 212Pb was measured using several HPGe detectors, ionization chambers, and a well-type NaI(Tl) detector.

A benchmark for Monte Carlo simulations in gamma-ray spectrometry Part II: True coincidence summing correction factors

The goal of this study is to provide a benchmark for the use of Monte Carlo simulation when applied to coincidence summing corrections. The examples are based on simple geometries: two types of germanium detectors and four kinds of sources, to mimic eight typical measurement conditions. The coincidence corrective factors are computed for four radionuclides. The exercise input files and calculation results with practical recommendations are made available for new users on a dedicated webpage.

Latent variable modeling of gamma-ray background in repeated measurements

We propose a novel approach for background subtraction in repeated gamma-ray spectrometric measurements. This entirely data-driven method eliminates the need for Monte Carlo detector simulation. To accomplish this, we utilized the framework of Latent Variable Modeling, incorporating various matrix factorization techniques and artificial neural networks. Subsequently, we applied this method to estimate radionuclide activity through spectrum unmixing. Significant improvements in sensitivity, surpassing traditional methods, were observed for the test case scenario of aerosol filter measurements.

Algorithm development for low level radioxenon 2D spectra analysis: A first case of study using spectral unmixing for a β-γ detector

In the scope of the verification regime of the Comprehensive nuclear Test Ban Treaty, the CEA/DAM is developing new β-γ measurement systems. In order to improve the analysis methods at low statistics, a new multiplicative spectral unmixing algorithm for full-spectrum analysis was tested on a particular setup for different types of mixtures. The reconstructed activities for simulated spectra and the characteristic limits found with this algorithm are compared to the classic ROI analysis method.

Towards a radon-in-water primary standard at LNHB

Despite widespread radon-in-water measurements, no primary radon-in-water standards currently exist. This work aims to bridge this gap by developing a system to produce radon-in-water reference materials. The system relies on cryogenic, loss-free transfer of radon, which is standardized through defined solid angle measurements, to a radon standard in water. It allows for preparation of liquid scintillation and gamma-ray spectrometry samples with traceable radon-in-water concentrations. The system's design, functionality, and the results of pilot performance tests are described.

Online spectral unmixing in gamma-ray spectrometry

We introduced in a previous paper a time-dependent full-spectrum analysis algorithm speeding up the estimation of the activity of the radionuclides present in a sample. In this paper, we present a new version of the algorithm allowing online estimation. It uses only on a buffer of few segments while keeping the time information by using a time dependent regularization, thus reducing the size of the data matrices and the length of the processing of each iteration. The algorithm is optimized and tested on both simulated and measured spectra of aerosol samples.

Measurement of Cumulative fission product yields on 235U induced by 2.8 MeV neutrons

Off-line gamma-ray spectrometry was used to accurately measure the Cumulative fission product yields (CFPYs) of fission products in the 235U (n, f) reaction induced by 2.8 MeV neutrons. The 2.8 MeV quasi-monoenergetic neutron beam was produced by the CPNG-600 Cockcroft Walton accelerator at the China Institute of Atomic Energy （CIAE）and the gamma spectra were measured by the HPGe γ-ray Spectrometer. After fully considering and revising the sources of uncertainty, high-precision CFPYs of 4 fission products were obtained. This study has important applications in reactor design and operation and is conducive to the establishment of an evaluated nuclear database.

Influence of phosphate fertilizers on the radioactivity of agricultural soils and tobacco plants in Kenya, Tanzania, and Uganda

Three brands of NPK fertilizers that contain variable concentrations of natural radioactivity are commonly used in tobacco plantations in Kenya, Tanzania, and Uganda. Tobacco plants are known for hyper-accumulation of natural radionuclides, particularly ²³⁸U. This study investigated if the elevated radioactivity in phosphate fertilizers could enhance radioactivity in soils and tobacco plant leaves. The ²³²Th, ²³⁸U, and ⁴⁰K radionuclide levels in NPK-fertilized soils and tobacco leaves were measured using gamma-ray spectroscopy. The research included a one-year reference experiment with tobacco growing in plots, a ten-year semi-controlled experiment in well-managed tobacco farms, and a field survey of radioactivity in soils and tobacco leaves at three traditional tobacco fields in Migori (Kenya), Urambo (Tanzania), and Kanungu (Uganda). The findings demonstrated that soils and tobacco leaves exposed to NPK fertilizers with increased radioactivity had activity concentrations of ²³²Th, ²³⁸U, and ⁴⁰K that were considerably higher (at all sites) than in the control samples (with no use of NPK fertilizers). As the continued application of NPK fertilizers raises concentrations of ²³²Th, ²³⁸U, and ⁴⁰K in agricultural soils, the study assessed radiological risks for humans from exposure to agricultural soils enriched with phosphate fertilizers, and it was found to be below the exposure limit of 1 mSvy^-1 suggested by the International Commission on Radiological Protection (ICRP). However, tobacco consumers, both by snuffing and smoking, may face significant radiological risks, as the snuffing and smoking resulted in effective doses that were 2.41 to 6.53 and 1.14 to 2.45 times greater than the average yearly dose that the general public receives from inhalation of natural radionuclides (United Nations Scientific Committee on Atomic Radiations estimates). Furthermore, the results indicate that the lifetime excess cancer risk for tobacco snuffers and smokers ranged from 5 × 10^-5 to 24.48 × 10^-3 and 2.0 × 10^-5 to 9.18 × 10^-3, respectively. The influence of phosphorus-derived fertilizer containing relatively high natural radioactivity, potential human radiation exposure, and radiological risk due to gamma radionuclides is estimated and discussed. The results reveal that applying phosphate fertilizers enhances natural radioactivity in soil and is subsequently influenced by soil to tobacco plant uptake. Therefore, the study recommends that countries use fertilizers with lower radionuclide content to conserve soil quality and reduce gamma-emitting radionuclides in tobacco plants.

Evaluating the intensity of the 803-keV γ ray of 210Po using a 4παβ(LS)-γ(HPGe) measurement system

The absolute intensity for the 803-keV γ ray of ²¹⁰Po was evaluated by α-γ coincidence technique. A liquid sample with a known amount of ²¹⁰Po embedded in scintillation fluid was measured in a coincidence-based system that comprises a Liquid Scintillator (LS) detector and a High-Purity Germanium (HPGe) detector. A photo-reflector assembly that contains the ²¹⁰Po sample provides 100% efficiency for detecting the α particles. The combination between the HPGe and the LS detectors allows to reject non-coincident α-γ events while maintaining high resolution γ spectroscopy. Consequently, the faint 803-keV photopeak from ²¹⁰Po could be observed in a background-free environment, and its intensity could be evaluated with good accuracy. Sample measurements were carried out over nine months to gather statistics and verify the reliability of the experimental procedure. The absolute intensity of the 803-keV line was found to be (1.22 ± 0.03) × 10^-5, in excellent agreement with the adopted value in a recent data compilation and consistent with previous experimental works.

Characterization of a 4παβ(LS)-γ(HPGe) prototype system for low-background measurements

A ground-level prototype system for low-background measurements was developed and tested. The system consists of a high-purity germanium (HPGe) detector used for detecting γ rays and coupled to a liquid scintillator (LS) used for detecting α and β particles. Both detectors are surrounded by shielding materials and anti-cosmic detectors ("veto") used to suppress background events. The energy and timestamp of detected α, β and γ emissions are recorded event-by-event and analyzed offline. By requiring timing coincidence between the HPGe and LS detectors, background events originating from outside the volume of the measured sample can be effectively rejected. The system performance was evaluated using liquid samples containing known activities of an α emitter (²⁴¹Am) or a β emitter (⁶⁰Co) whose decays are accompanied by γ rays. The LS detector was found to provide a solid angle of almost 4π for α and β particles. Compared to the traditional γ-singles mode, operating the system in coincidence mode (i.e., α-γ or β-γ) reduced the background counts by a factor of ∼100. Consequently, the minimal detectable activity for ²⁴¹Am and ⁶⁰Co was improved by a factor of 9, being 4 mBq and 1 mBq for an 11-d measurement, respectively. Furthermore, by applying a spectrometric cut in the LS spectrum that corresponds to α emission from ²⁴¹Am, a background reduction factor of ∼2400 (compared to γ-singles mode) was achieved. Beyond low-background measurements, this prototype exhibits additional compelling features, such as the ability to focus on certain decay channels and study their properties. This concept for a measurement system may be of interest to laboratories that monitor environmental radioactivity, studies involving environmental measurements and/or trace-level radioactivity.

Natural and artificial radioactive pollution in sediment and soil samples of the Bosphorus, Istanbul

This study focused on the determination of natural (²³⁸U, ²³²Th, and ⁴⁰K) and artificial (¹³⁷Cs) radionuclide concentrations both in 55 sediment samples collected from various depths in the Bosphorus and 5 soil samples from the coastline of the Bosphorus, Istanbul, using gamma-ray spectrometry with an HPGe detector. The mean activity concentrations of natural ²³⁸U, ²³²Th, and ⁴⁰K and anthropogenic ¹³⁷Cs were determined to be 11.41 ± 0.21 Bq kg^-1, 6.87 ± 0.16 Bq kg^-1, 369.61 ± 3.41 Bq kg^-1, and 6.54 ± 0.11 Bq kg^-1, respectively, in the sediment samples. The average activity concentrations of ²³⁸U, ²³²Th, ⁴⁰K, and ¹³⁷Cs radionuclides in the soil samples were also measured to be 11.65 ± 0.18 Bq kg^-1, 9.55 ± 0.15 Bq kg^-1, 369.43 ± 3.09 Bq kg^-1, and 4.57 ± 0.09 Bq kg^-1, respectively. Radiological contour maps based on the activity concentrations of natural and artificial radionuclides in the sediment samples for the Bosphorus, Istanbul, were created. The total annual effective doses due to soil samples were calculated to be 34.58 μSv y^-1.

Chemical separation and measurement of platinum activation products

A method has been developed to purify and measure platinum radioisotopes in the presence of fission products and environmental constituents. The method uses a combination of cation exchange and anion exchange chromatography and selective precipitation steps to remove other radioisotopes from the sample. The addition of stable platinum carrier allows for a gravimetric determination of the chemical yield of the procedure. Overall, the method is fast, simple, and potentially applicable for rapid turnaround of unknown samples. Using this method, multiple platinum radioisotopes were measured in two different irradiation experiments. The measured ratios of the platinum radioisotopes clearly reflect the neutron spectrum of the irradiation, suggesting that platinum radioisotopes could be valuable signatures in nuclear forensic analyses.

Cosmogenic radionuclides in the Cavezzo meteorite: Gamma-ray measurement and detection efficiency simulations

The Cavezzo meteorite was recovered on January 4^th, 2020, just three days after the fall observed over Northern Italy by the all-sky cameras of the Italian PRISMA fireball network. Two specimens, weighing 3.1 g (F1) and 52.2 g (F2), were collected in the predicted strewn-field and the meteorite has been classified as an L5 anomalous chondrite. The gamma-activity of the F2 sample was measured at the Monte dei Cappuccini underground Research Station (Torino, Italy) with a large-volume HPGe-NaI(Tl) spectrometer. Thanks to the high efficiency, selectivity, and low background of the spectrometer, we were able to detect fifteen cosmogenic radioisotopes. The presence of nuclides with half-lives down to a few days (⁴⁷Ca, ⁵²Mn, and ⁴⁸V) undoubtedly confirmed the recent fall of the sample. The very low activity of ⁴⁴Ti and ⁶⁰Co was revealed with a particular coincidence between the HPGe and NaI(Tl) detectors. To obtain the detection efficiency, we have simulated the response of the detector with the GEANT4 toolkit, once the spectrometer's dead layer thickness was estimated using standards of known activity. Moreover, the simulation of the Dhajala meteorite (H3/4 chondrite) measurement allowed us to verify that the self-absorption of the sample is correctly taken into account and validate our simulations. In this contribution, we focus on the coincidence optimization techniques and the detection efficiency computation.

Validation of efficiency transfer for high-density materials in HPGe spectrometry

Recycling and conventional reuse of lead materials and structures originating from controlled areas in nuclear facilities rely on historical knowledge and well selected characterization procedures. At the SCK•CEN, one of these procedures involves performing high-resolution gamma-ray spectrometry measurements on several cylindrical shaped test samples (50 mm diameter and approximately 5 mm thickness), obtained during the lead melting campaigns. The high density (11.3 g/cm³) of these samples is a challenge for radionuclide analysis by gamma-ray spectrometry since no such calibration sources nor reference materials are available. We used the efficiency transfer procedure, relying on regular standard sources available in our laboratory, to set up calibrations for this specific counting geometry. The method proves to be fit for purpose.

A new efficiency calibration methodology for different atmospheric filter geometries by using coaxial Ge detectors

The study of the different pollutants present in atmospheric aerosols such as trace elements and radionuclides is essential to assess the air quality. To analyze the particulate matter (PM), atmospheric filters with different dimensions and geometries (rectangular, circular, slotted, and square filters) are usually employed. Regarding the pollutants existing in atmospheric aerosols, radionuclides are usually analyzed due to their multiple applications such as either in the environmental radiological control or as tracers of atmospheric processes. Therefore, this study aims to develop a new and general methodology to calibrate in efficiency coaxial Ge detectors to properly determine radionuclides present in the PM by gamma-ray spectrometry for several filter types. For this, granular certified reference materials (CRM) containing only natural radionuclides (238U-series, 232Th-series, and 40 K) were selected. Several granular solid CRMs were chosen allowing us to reproduce the same PM deposition geometry and to assure the homogeneity of the added CRMs. These are the main advantages in relation to the typical methods that use liquid CRMs. Furthermore, for filters whose surfaces are relatively large, they were cut in several pieces and placed one on top of the other, achieving the same geometry than the PM deposited onto the filter. Then, the experimental full-energy peak efficiencies (FEPEs) were obtained for each energy of interest (Eγ) and they were fitted versus Eγ, finding a general FEPE function for each filter type. Finally, this methodology was validated for both natural and artificial radionuclides (from 46 to 1332 keV) by using different filter types employed in proficiency test exercises, obtaining |zscore|< 2 for all cases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11869-023-01336-x.

Assessment of natural radiation in contaminated automobile workshop soils

The presented study aims to identify and quantify the natural radionuclides activity concentrations on the top and sub-soils around mechanic workshops in Ojo and Ijegun, Lagos, Nigeria. Based on these measured radionuclides activity concentrations, radiological hazard indices are assessed. Twenty oil-contaminated soil samples were collected, and the levels of natural radionuclides activity are measured by applying gamma spectrometry The measured radionuclides with authoritative regularity are linked with the natural decay series of ²³⁸U (²²⁶Ra) and ²³²Th as well as the series of non-decay ⁴⁰K. The obtained results show that the mean radionuclides activity concentrations in the collected oil-contaminated soils samples are 14 ± 4 Bq kg^-1, 105 ± 55 Bq kg^-1, and 90 ± 33 Bq kg^-1, for ²²⁶Ra, ²³²Th, and ⁴⁰K respectively. It was founded that the ²²⁶Ra radionuclide is the lower present in the oil-contaminated soils samples. The radiological assessments were evaluated in terms internal hazard index (0.54), and external hazard index (0.55) both of which are below the UNSCEAR-2000 standard limit. Consequently, the radiological assessment indicated that long-time exposure to those radionuclide's strength confuses integral hazards.

A methodology to determine 212Pb, 212Bi, 214Pb and 214Bi in atmospheric aerosols; Application to precisely obtain aerosol residence times and Rn-daughters' equilibrium factors

Progeny of ²²²Rn and ²²⁰Rn, (²¹²Pb, ²¹²Bi, ²¹⁴Pb and ²¹⁴Bi) are essential to assess radiological hazard, external and internal doses, residence times and equilibrium factors. Precise measurements of these nuclides are quite complex due to their very short half-lives. This study outlines a new and precise methodology to measure these nuclides. Radon-222 and ²²⁰Rn were measured using a radon monitoring system, while their respective progenies were collected in an atmospheric filter using an ASS-500 sampler and measured by gamma-ray spectrometry. The ²¹²Pb concentrations were very similar to the thoron ones, where all ²¹²Bi/²¹²Pb ratios were consistently less than 1. The relative uncertainties, σ_r, of the ²¹²Pb and ²¹²Bi activity concentrations, and ²¹²Bi/²¹²Pb activity ratio are generally less than 10%. Moreover, ²¹⁴Pb/²²²Rn ratios were about 0.7, agreeing well with previous works. The σ_r for ²¹⁴Pb, ²¹⁴Bi and ²¹⁴Bi/²¹⁴Pb were generally less than 6%. This methodology was applied to estimate aerosol residence times using the ²¹⁴Pb/²²²Rn and ²¹²Bi/²¹²Pb activity ratios, and to obtain equilibrium factors, achieving consistent results. Furthermore, the methodology consistency and validity range were studied with time elapsed between sampling end and counting start, and the sampling durations, finding the optimum times to precisely determine ²¹²Pb, ²¹²Bi, ²¹⁴Pb and ²¹⁴Bi.

Calculation of decision thresholds according to the standard ISO 11929-3 in case of presence of the peaked background

The method of calculation of the decision threshold with the Least Squares Method, described in the standard ISO 11929, is presented for the case when the sources of peaked background contribute to the peak holding the indication. The decision threshold is calculated from spectral data corresponding to the indication zero; therefore, the observed indication must be removed from the spectrum. When the peaked background is present, the indication completely overlaps with the peaked background, so it can't be unfolded directly. Therefore, two steps are needed in the calculation: the unfolding of the peak, housing the indication, from the continuous background and the possible overlapping peaks, and separating of the indication from the peaked background using the background data obtained from separate calculations and measurements. In this article it is shown that the method of least squares is flexible enough to accommodate all sources of uncertainty into the uncertainty matrix of input quantities. Its derivation is presented in detail and the calculation of the indication corresponding to the decision threshold is described. As a proof of the concept an example of calculating the number of counts corresponding to the decision threshold as a function of the indication is presented. The method of calculation and the results of the calculation are briefly discussed.

ASSESSMENT OF GAMMA DOSE AND ANNUAL EFFECTIVE DOSE RATE FOR COMMONLY USED FERTILIZER SAMPLES IN AGRICULTURE FIELD WITH A STATISTICAL APPROACH

In this present study, the activity concentration of the naturally occurring radionuclides 238U, 232Th and 40K have been measured in commonly used chemical fertilizers for agriculture by using gamma-ray spectrometry with NaI (TI) detector. Radiological hazard parameters have been calculated for samples. The mean specific activity concentration of the 238U, 232Th and 40K is 176, 5.75 and 4136 Bq kg-1, respectively. Particularly, the mean value of 238U, as well as 40K, is higher than the world recommended value. Also, the average value of radium equivalent activity is 503 Bq kg-1 and the absorbed dose rate (DR) is 282.93 nGyh-1, which is greater than the permissible limit, whereas the annual effective dose rate (AEDR) is 0.316 mSvy-1, which is lower than the world recommended value. Therefore, collected fertilizer samples significantly increase the activity concentration of natural radionuclides in the agricultural soils. Multivariate statistical techniques such as Pearson correlation and factor analysis are carried out for radioactive variables to understand the existing relationship between them. From obtained results reveals that these fertilizer samples increases the probability of adverse health effects due to natural radioactivity.

A simple and precise methodology to determine particulate matter mass in atmospheric filters; validation and application cases

In the past decades, particulate matter (PM) measurements have been used extensively in atmospheric sciences, as it allows studying the evolution of tracers for different atmospheric processes and the effects of atmospheric pollution on human health. However, measuring PM mass requires a constant control of the laboratory conditions due to its capacity to absorb humidity. For this reason, this study was focused on developing a novel, simple and precise methodology to determine the corrections of the filter mass due to humidity changes. The control and corrections are possible using a "control filter", which is always adapted to the environmental conditions of the laboratory. To check the consistency of this method, it was proved that the mass of any problem filter and that of the control filter behave in a very similar way. This allows quantifying the mass changes of any problem filter by using the control filter, where the problem filters and the control filter must have the same chemical composition and dimensions. To validate this methodology, a comparison was made between the methodology proposed in this study (Method-1) and the one proposed by the EPA (Method-2), which is generally applied. The particulate matter mass (m) was obtained for a problem filter for different weights, achieving similar values using both methods. However, Method-1 still provided reliable mass measurements for relative humidities very different from 50%, even as low as 18%. It was also proved that the adsorption or loss of water by the particulate matter can be neglected, since m is much smaller than the blank filter mass. Method-1 was also employed in several samplings carried out using three PM₁₀ samplers to determine contaminants, such as ⁷Be and ²¹⁰Pb, obtaining a good agreement between all particulate masses and activities measured by the three samplers for all samplings.

A rapid method for determining low concentrations of 210Pb in drinking water using MnO2 fibers

A rapid method for determining low activity concentrations of ²¹⁰Pb in drinking water was developed and tested. The method consists of a few stages for sample preparation that involve passing 12 L of water through a column with acrylic fibers implanted with MnO₂ (used to adsorb ²¹⁰Pb). The MnO₂ fibers are oven-dried, compressed and measured by a broad-energy germanium detector used to quantify ²¹⁰Pb via its characteristic 46.5 keV γ-ray. The time taken for sample preparation is approximately 4 h and recovery factors for lead in tap water of 87 ± 3% were achieved. After a measurement duration of 4 h, the minimum detectable activity concentration reaches 0.02 Bq/L for ²¹⁰Pb, being well below the respective limit for drinking water in Israel (0.2 Bq/L) as well as the value recommended by the World Health Organization (0.1 Bq/L). Furthermore, a measurement duration of 48 h provides a minimum detectable activity concentration of ∼0.006 Bq/L, which is similar in magnitude to other, well-established methods that rely on lengthy and rather complex procedures. Thus, the combination of MnO₂ fibers and gamma-ray spectrometry may be attractive for routine use by analytical laboratories that monitor radioactivity in drinking water.

Evaluating the intensity of the 'prompt' 140.5 keV γ-ray of 99Mo using a 4παβ(LS)-γ(HPGe) measurement system

The absolute intensity for the 'prompt' 140.5 keV gamma-ray of ⁹⁹Mo was evaluated using the β-γ coincidence technique. A liquid sample of ⁹⁹Mo was prepared from a⁹⁹Mo/^99mTc generator and measured in a 4παβ(LS)-γ(HPGe) system that comprises a Liquid Scintillator (LS) detector and a High-Purity Germanium (HPGe) detector. The sample was introduced into scintillation fluid embedded in a photo-reflector assembly that provides almost 100% efficiency for detecting β particles (in the energy range of intreset). The combination of the HPGe and the LS detectors provided a highly effective rejection mechanism for non-coincident events. Thereby, the distinction between the detected 140.5 keV events originating from decays of ^99mTc (IT) and those from transitions bypassing the metastable state could be obtained and the 'prompt' intensity was evaluated directly. The system was calibrated for detecting β particles and γ-rays using radioactive sources of known activities and having identical geometry as the sample containing ⁹⁹Mo. The absolute intensity of the 'prompt' 140.5 keV was found to be (5.21 ± 0.02_stat±0.16_sys)%, in good agreement with results from more recently reported works.

Evaluation of natural radioactivity levels and potential radiological hazards of common building materials utilized in Mediterranean region, Turkey

Radiometric measurement of building materials is very important to assess the internal and external exposure caused by the ionizing radiation emitted from terrestrial radionuclides in building materials. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K in fifty-eight samples of fifteen different structural and covering building materials commonly used in Osmaniye province located in the Mediterranean region of Turkey were measured by using gamma-ray spectroscopy. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K varied from 2.5 ± 0.1 (marble) to 145.7 ± 4.4 (clay brick), 1.3 ± 0.1 (marble) to 154.3 ± 4.1 (marble), and 8.6 ± 0.2 (sand) to 1044.1 ± 70.3 (granite), respectively. Radiological parameters (activity concentration index, alpha index, indoor absorbed gamma dose rate and the corresponding annual effective dose rate, and excess lifetime cancer risk) were estimated to evaluate the health hazards associated with these building materials. Since the estimated values of these parameters are within the recommended safety limits or criteria values, the use of the studied building materials in the construction of dwellings can be considered to be safe for the residents of the region.

Radioactive fossils: The uranium anomaly and its paleobiological implications

In this study, several natural radionuclides (⁴⁰K, ²³⁸U, ²³⁵U, ²²⁸Ac) and their decay product were investigated in various invertebrate and vertebrate fossils. In the high radioactivity group of fossils, ²³⁸U and ²³⁵U concentrations increased from 141 to 3621 Bq/kg and from 5.4 to 167 Bq/kg, respectively. In the low radioactivity group of fossils, concentrations of both U isotopes increased from 4.6 to 51 Bq/kg and from 0.18 to 2.3 Bq/kg, respectively. High radioactivity has been linked to the phosphatization process that affected the uranium sorption. Scanning of electron microscope images and X-ray fluorescence analysis were used to confirm the mode of preservation of studied fossils and the presence of a correlation between the phosphorus content and uranium elements in fossil specimens.

Natural radioactivity and radiological risks of common building materials used in Semnan Province dwellings, Iran

Impact assessment of building materials is a focused topic in the field of radioecology. A radiological survey has conducted to monitor radioactivity of most common building materials in Semnan Province, Iran, and assess the radiation risk. Activity concentrations of 226Ra, 232Th, and 40K were measured in 29 samples including nine commonly used building materials that were collected from local suppliers and manufacturers, using a high purity germanium gamma-ray detector. The activity concentrations of 226Ra, 232Th, and 40K varied from 6.7±1 to 43.6±9, 5.9±1 to 60±11, and 28.5±3 to 1085±113 Bq kg-1 with averages of 26.8±5, 22.7±4, and 322.4±4 Bq kg-1, respectively. By applying multivariate statistical approach (Pearson correlation, cluster, and principal component analyses (PCA)), the radiological health hazard parameters were analyzed to obtain similarities and correlations between the various samples. The Pearson correlation showed that the 226Ra distribution in the samples is controlled by changing the 232Th concentration. The variance of 95.58% obtained from PCA resulted that the main radiological health hazard parameters exist due to the concentration of 226Ra and 232Th. The resulting dendrogram of cluster analysis also shows a well coincidence with the correlation analysis.

Possibilities of the use of CeBr3 scintillation detectors for the measurement of the content of radionuclides in samples for environmental monitoring

The investigation of radioactivity in samples is an application of gamma-ray spectrometry dealing with low and very low level gamma-ray activities of different isotopes. Gamma-ray spectrometry performed in the framework of radiological environmental monitoring may be done after selective sampling processes or after a chemical purification of a sample. Both cases imply that only some specific radionuclides should contribute to the obtained spectrum. Gamma-ray spectrometry performed with medium energy resolution detectors may allow the possible distinction of their photopeaks. Therefore, a cerium bromide (CeBr₃) detector can be particularly attractive for routine tasks in radiological environmental monitoring as it has a high efficiency, medium energy resolution and it can work at room temperature. This study describes the conditions under which a CeBr₃ detector can serve for some routine analysis in radiological analysis of samples collected in the environment or collected by air-samplers in environmental radiological monitoring programmes.

Gamma-ray spectroscopy with anode pulses of NaI(Tl) detector using a low-cost digitizer system

Recently, digital gamma-ray spectroscopy employing low-cost and publicly available (Commercial off the shelf) digitizers has been frequently used in different studies worldwide. In this paper, we considered the digital methods for gamma-ray spectroscopy in which the anode pulses of the photomultiplier tube (PMT) output in a NaI(Tl) scintillation detector were immediately digitized by a PC sound card. We introduced and developed the methods for gamma-ray spectroscopy of microCurie gamma-ray sources by a sampling rate of 96 kHz. First, at low count rates, the pulse arrival time was determined directly by the raw waveform, and the gamma-ray spectrum was obtained by summing the corresponding values in the samples per pulse. In addition, the gamma-ray spectrum was obtained by an enhanced sampling rate waveform and the pulse arrival time was determined by employing the digital constant fraction discrimination (DCFD) method, where each pulse area was achievable by summing the corresponding values of pulse samples. On the other hand, fitting the appropriate model function on the pulses and obtaining the fitted pulse area were undertaken for gamma-ray spectroscopy. To this end, a non-iterative algorithm to fast fit the Gaussian model function was improved. Moreover, the pile-up correction was performed at different count rates employing the Maximum Likelihood Estimation (MLE) method and Gaussian model function. Also, an approximate method for solving the high run time challenge was identified in the MLE method for long-time waveforms. To reject the pile-up events, a method was introduced based on the calculation of the full-width at half maximum pulses. By applying the proposed rejection method, we achieved an energy resolution of 6.2% at 663 keV gamma-rays and a count rate of 5.3 kcps.

Determination of the gamma and X-ray emission intensities of erbium-169

The gamma and X-ray emission intensities of ¹⁶⁹Er were determined using radionuclidically pure ¹⁶⁹Er. The activity of the ¹⁶⁹Er source was standardized by the triple-to-double-coincidence ratio technique. Three independent measurements were performed to measure the emission intensities using calibrated high-purity germanium spectrometers. The efficiencies were computed with the Monte Carlo method and validated using several experimental measurements. Final results present a large uncertainty reduction compared to previous evaluations. The emission intensities per decay of ¹⁶⁹Er are reported as 1.401(40).10^-5 for the 109.8 keV line and 1.513(19).10^-6 for the 118.2 keV line. The values obtained for the X-ray lines show large discrepancies with the reference values.

Ra-224 activity, half-life, and 241 keV gamma ray absolute emission intensity: A NIST-NPL bilateral comparison

The national metrology institutes for the United Kingdom (UK) and the United States of America (USA) have compared activity standards for 224Ra, an α-particle emitter of interest as the basis for therapeutic radiopharmaceuticals. Solutions of 224RaCl2 were assayed by absolute methods, including digital coincidence counting and triple-to-double coincidence ratio liquid scintillation counting. Ionization chamber and high-purity germanium (HPGe) γ-ray spectrometry calibrations were compared; further, a solution was shipped between laboratories for a direct comparison by HPGe spectrometry. New determinations of the absolute emission intensity for the 241 keV γ ray (Iγ = 4.011(16) per 100 disintegrations of 224Ra) and of the 224Ra half-life (T1/2 = 3.6313(14) d) are presented and discussed in the context of previous measurements and evaluations.

Evaluation of radionuclide concentrations and average annual committed effective dose due to medicinal plants and soils commonly consumed by pregnant women in Osukuru, Tororo (Uganda)

The intention of the study was to establish the activity concentrations and the annual committed effective dose due to ingestion of medicinal plants and soils by pregnant women and their probable effects to infants. The samples of medicinal plants and soils were collected from Osukuru, Tororo District (Uganda). The naturally occurring radionuclides investigated were ²²⁶Ra, ²³²Th and ⁴⁰K and their activity concentrations were determined using NaI gamma detector. In the medicinal plants, the average activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K were found to be 6.04 Bq/kg, 9.65 Bq/kg and 359.59 Bq/kg respectively. African Basil registered the highest activity concentration of ²²⁶Ra of 10.02 Bq/kg, spider plant had the highest activity concentration of ²³²Th of 18.60 Bq/kg whereas the pumpkin registered the highest activity concentrations of ⁴⁰K of 437.92 Bq/kg. The average activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in 'medicinal soils' were 68.87 Bq/kg, 78.20 Bq/kg and 477.44 Bq/kg respectively. The soils from the anthills registered the highest activity concentration of ²²⁶Ra and ⁴⁰K while the one from bricks registered the highest activity concentration of ²³²Th. The annual committed effective dose due to the ingestion of medicinal plants varied from 0.096 to 0.297 mSv/y with an average of 0.194 mSv/y in infants, 0.016-0.040 mSv/y with an average of 0.029 mSv/y for individuals of age range 12-17 years and 0.007-0.018 mSv/y with an average of 0.013 mSv/y for individuals older than 17 years. Whereas the annual committed effective dose due to the ingestion of 'medicinal soils' varied from 1.28 to 1.65 mSv/y with an average of 1.46 mSv/y in infants, 0.23-0.30 mSv/y with an average of 0.26 mSv/y (12-17 years) and 0.07-0.09 mSv/y with an average of 0.08 mSv/y for individuals older than 17 years. In medicinal plants, the annual committed effective dose for the all age groups examined were below 0.3 mSv/y (maximum world permissible as reported UNSCEAR, 2000) while that due to the ingestion of 'medicinal soils' had values higher 0.3 mSv/y in infants. The results of this study show that there is inherent danger to the infants in consuming soils during pregnancy and this should be discouraged.

Comparison of three analytical techniques for determination of Th and U in environmental samples

Alpha-particle spectrometry, gamma spectrometry and neutron activation analysis techniques for determination of Th and U in environmental samples have been compared. The analytical parameters studied include detection limit, accuracy, repeatability, reproducibility and surrogate recovery. The results show that neutron activation analysis technique has the best accuracy among the studied techniques; the other two techniques were assessed relative to it. The percentage difference between the three techniques results is about [-20, 20]. In addition, U and Th concentrations are generally overestimated by gamma spectrometry and alpha-particle spectrometry in all cases except Th concentration in the former technique, which is underestimated.

Calibration and use of well-type germanium detectors for low-level gamma-ray spectrometry of sediments using a semi-empirical method

Gamma-ray spectrometry is a widely used technique to quantify the presence of numerous radionuclides in environmental samples. In this work, we describe a methodology for efficiency calibration of four well-type germanium detectors and their use for the determination of low-level activities of gamma emitters in sediment samples. An experimental efficiency calibration for each detector was built with three materials for 17 energies, ranging from 46.5 keV to 1460 keV. For efficiency transfer to different geometries and sample types, we used the effective solid angle approach (ET-Ω method). Final calibrations were calculated for all detectors, several counting geometries, and elemental composition of selected sample types. Calibrations were validated with six reference materials. This methodology allowed to reliably analyze nine gamma emitters (²¹⁰Pb, ²⁴¹Am, ²³⁴Th, ²²⁸Ac, ²¹⁴Pb, ²⁰⁸Tl, ¹³⁷Cs, ¹³⁴Cs and ⁴⁰K) in sediment samples. Using these calibrations, gamma emitter profiles of sediment cores from contrasting aquatic systems (lake, intertidal, marine and deep-sea areas) provided reliable profiles of ²¹⁰Pb and artificial radionuclides useful for dating and stratigraphic interpretation. A protocol to implement this methodology is also presented.

Determination of the half-life and the absolute photon emission intensities for the main gamma-ray energies of 124I

The National Institute of Standards and Technology (NIST) performed new standardization measurements for ¹²⁴I. As part of this work the absolute photon emission intensity for the main gamma-rays of ¹²⁴I were determined using several high-purity germanium (HPGe) detectors. In addition, the half-life for ¹²⁴I was also determined using an HPGe detector. Ionization chamber measurements were performed for additional sources, but it was not possible to obtain a precise half-life value.

Measurement of the absolute gamma-ray emission intensities from the decay of 103Pd

Palladium-103 decays through electron capture to excited levels of ¹⁰³Rh, and especially to the 39.748-keV metastable state. A high activity palladium chloride solution was standardized by liquid scintillation, using the Triple-to-Double Coincidence Ratio method. The absolute photon emission intensities were determined by gamma-ray spectrometry using point sources prepared with the standard solution. Different detectors and measuring conditions were used to cross-reference the results. The most intense photon emission intensities are derived with about 1% relative combined standard uncertainty.

A large buoy-based radioactivity monitoring system for gamma-ray emitters in surface seawater

A buoy (shallow water light type) -based in situ gamma-ray spectrometry system with a 7.6 cmØ × 7.6 cm NaI(Tl) detector for remote real-time monitoring of gamma-ray emitting radionuclides in surface seawater is presented. To convert measured count rates to radioactivity, the full energy peak efficiency of the detector for radionuclides in seawater was estimated using Monte Carlo simulation with the MCNP code. The efficiency calibration was validated by comparing the results with a sampling analysis of ⁴⁰K in seawater at the sites where the monitoring systems were deployed. The minimum detectable activity of the system for ¹³⁷Cs, ¹³⁴Cs and ¹³¹I with gamma-ray measurement time is discussed.

Distribution of uranium and thorium chains radionuclides in different fractions of phosphogypsum grains

This work presents results obtained using gamma spectrometry measurements of phosphogypsum samples on a non-fractionated (native) and fractionated phosphogypsum byproduct. The phosphogypsum was divided into particles size fractions within the range of < 0.063, 0.063-0.090, 0.090-0.125, 0.125-0.250, and over 0.250 mm and analyzed after reaching radioactive equilibrium using high-resolution gamma spectrometry technique. It was found that there is no significant differentiation between ²²⁶Ra distribution among particular grain size fractions of this material; however, tendency for preferential retention of radionuclides in particular grain size fractions is observed. The detailed analysis of results revealed that radium is preferentially retained in smaller grain size fractions, whereas lead and thorium in coarse fractions. The results indicate that overall ²²⁶Ra activity concentrations between particular fractions of phosphogypsum vary globally between - 34 and + 47% regarding non-fractionated material, and for ²¹⁰Pb activity concentration, fluctuations are found between - 26 up and + 38%. Presumably, the mechanism of radium incorporation into gypsum phase is based on a sequence of radium bearing sulfate phases formation followed by a surface adsorption of these phases on the calcium sulfate crystals, whereas for lead and thorium ions, rather incorporation into crystal lattice should be expected as more likelihood process.

Consistency test of coincidence-summing calculation methods for extended sources

An internal consistency test of the calculation of coincidence-summing correction factors F_C for volume sources is presented. The test is based on exact equations relating the values of F_C calculated for three ideal measurement configurations. The test is applied to a number of 33 sets of F_C values sent by 21 teams. Most sets passed the test, but not the results obtained using the quasi-point source approximation; in the latter case the test qualitatively indicated the magnitude of the bias of F_C.

Determining the probability of locating peaks using computerized peak-location methods in gamma-ray spectra as a function of the relative peak-area uncertainty

The probabilities of locating peaks with a high relative peak-area uncertainty were determined empirically with nine types of peak-location software used in laboratories engaged in gamma-ray spectrometry measurements. It was found that it is not possible to locate peaks with a probability of 0.95, when they have a relative peak-area uncertainty in excess of 50%. Locating peaks at these relatively high peak-area uncertainties with a probability greater than 0.95 is only possible in the library-driven mode, where the peak positions are supposed a-priori. The deficiencies of the library-driven mode and the possibilities to improve the probabilities of locating peaks are briefly discussed.

On the equivalence between homogeneously prepared sources and sources prepared by seeding in layers for different geometries, energies and matrix parameters

Measuring the radioactive content of environmental samples requires the use of appropriate reference materials with the same composition and density as the matrices to be measured. If they are not available, ad hoc artificially spiked reference materials are an alternative. Spiking in layers requires a detailed study of the drop distribution, as energy and decay scheme of the component radionuclides must be taken into account to produce a reference material that represents, in efficiency terms, a real sample. A method based on Monte Carlo simulation has been developed to find the optimal distribution of drops in layers for the combination of two typical soil samples and four radionuclides. Results have been validated by comparison with samples prepared by two techniques: methanol bath and spiking in layers.

A benchmark for Monte Carlo simulation in gamma-ray spectrometry

Monte Carlo (MC) simulation is widely used in gamma-ray spectrometry, however, its implementation is not always easy and can provide erroneous results. The present action provides a benchmark for several MC software for selected cases. The examples are based on simple geometries, two types of germanium detectors and four kinds of sources, to mimic eight typical measurement conditions. The action outputs (input files and efficiency calculation results, including practical recommendations for new users) are made available on a dedicated webpage.

Radioactive heat production of Syrian territory

Gamma-ray spectrometry is applied to estimate equivalent uranium (eU), equivalent thorium (eTh), and K% of 748 rock samples collected from Syrian territory. The spectrometry results are used to evaluate and map the radioactive heat production (HP) of Syria. A new approach involving the multifractal technique with the concentration-number model (CN) and log-log plots was originally proposed and hence applied in this paper to map the distribution of uranium concentration and HP of Syria. This approach helps us to differentiate different eU and HP ranges related to different litho-types. The advantages of proposing and applying the fractal technique are that the boundaries of the distinguished radioactive ranges of eU and HP coincide well with the lithological boundaries, which gives this technique superiority over other traditional statistical methods. The fractal CN model with the use of log-log plots proves its efficacy in differentiating between several eU and HP populations that are related directly to the geology of Syrian territory. The fractal model shows four threshold break points corresponding to uranium concentrations of 3.1, 7.38, 16.6, and 28.8 ppm and an HP of 0.715, 1.86, 3.63, and 6.26 μW/m³, respectively. The highest HP ranges are mainly related to the phosphatic deposits, characterized by the highest uranium content.

Comprehensive study on the technical aspects of sampling, transporting and measuring radon-in-water

The European Commission's Joint Research Centre organizes proficiency tests (PT) on radon-in-water measurements. In order to optimize sampling, transport and measurement methods many tests and small scale proficiency tests have been performed. The waters from natural springs, wells were sampled on-site in glass bottles then transported cooled to the JRC and collaborating laboratories. For the material characterization standard measurement methods based on gamma-ray spectrometry, emanometry and liquid scintillation counting were used. The influence of sampling, transport and sample handling on radon-loss was tested and quantified. It was observed that parameters like container material, filling height, storage temperature and handling can lead to substantial measurement bias due to radon-loss. This high risk for radon-loss from samples can potentially be a general radioprotection problem as doses to the public may be underestimated. Regular air and road transport can be considered adequate means of transport as they have little influence on radon-loss if a suitable glass sample container with flexible cap is used and that it is completely filled. On the basis of this work, modifications to the related standard as best practices are also proposed.

Methods, results and dose consequences of 106Ru detection in the environment in Budapest, Hungary

From late September to early October of 2017, the majority of European networks involved in environmental radiological monitoring - including the environmental monitoring system of the KFKI Campus in Budapest - detected ¹⁰⁶Ru isotope of artificial origin in the atmosphere. The reported values higher than the minimum detectable activity (MDA) concentrations were in the range of 0.8 μBq/m³ - 145 mBq/m³. Based on the results of environmental measurements and the available meteorological data, assessments were made to analyze concentration levels of ¹⁰⁶Ru activity and to help understand the behavior of radioruthenium in various environmental media. Evaluation of the daily variation of activity levels indicated a maximum of 4 day-long residence time of ¹⁰⁶Ru contamination presence in ground level air in Budapest. An average ¹⁰⁶Ru activity concentration of 25.6 ± 1.4 mBq/m³ have been observed for the estimated residence time of ¹⁰⁶Ru in the air. Deposition of ¹⁰⁶Ru was dominantly influenced by rainfall, the major contributor wet deposition which led to an average of 11.3 ± 1.3 Bq/m² deposition on the ground surface prior to plume passage.

Medical activated charcoal tablets as a cheap tool for passive monitoring of gaseous 131I activity in air of nuclear medicine departments

It is well known that monitoring of radioactivity released from nuclear medicine departments is necessary to ensure the radiological safety of patients and personnel. Unfortunately, equipment for air sampling is often expensive, loud and is not suitable to use in hospitals. Our goal was to find cheap and simple system for passive monitoring of ¹³¹I activity concentration in the air of nuclear medicine departments. Medical activated charcoal tablets were used, because charcoal is excellent material for ¹³¹I trapping and tablets are readily available. Our proposed sampling protocol contains tablets preparation, exposure and measurements using HPGe detector. Different methods of tablets preparation (drying, impregnation with KI or NaOH) were tested while an experimental chamber was prepared for estimating ¹³¹I (released from Na¹³¹I, similar to that used in therapy) trapping efficiency of tablets in different conditions. Finally, tablets were placed in plastic holders and tested in nuclear medicine facilities.

Use of Genie 2000 and Excel VBA to correct for γ-ray interference in the determination of NORM building material activity concentrations

The γ-radiation emitted by building materials is calculated from the activity indices for ²³²Th, ²²⁶Ra and ⁴⁰K and expressed as the activity concentration index (ACI). Gamma spectroscopy is a non-destructive technique frequently used to simultaneously determine the indices for several radionuclides. Spectral interpretation poses a number of challenges, including identification of γ-lines subject to summing-in effects, interference from other γ-ray emitting radionuclides and the time required to reach secular equilibrium. These challenges are not fully addressed by Canberra Industries' Genie 2000, the software used by many laboratories to analyse samples. This article describes a Microsoft Excel workbook that exploits Genie 2000 flexibility to program applications with Visual Basic using Canberra's Nuclear Data Access Library and batch procedure tools. The workbook determines ⁴⁰K activity concentration after correcting for ²²⁸Ac interference and ²²⁶Ra activity directly from the γ-peak at 186.5 keV. The method proposed was tested by participating in 13 national and international scale inter-comparison exercises. The results were statistically indistinguishable from the reference values at a coverage factor of k = 3 and no statistically significant differences were identified between the respective means by a Student's t pairwise comparison.

Reconstructing the deposition environment and long-term fate of Chernobyl 137Cs at the floodplain scale through mobile gamma spectrometry

Cs-137 is considered to be the most significant anthropogenic contributor to human dose and presents a particularly difficult remediation challenge after a dispersal following nuclear incident. The Chernobyl Nuclear Power Plant meltdown in April 1986 represents the largest nuclear accident in history and released over 80 PBq of ¹³⁷Cs into the environment. As a result, much of the land in close proximity to Chernobyl, which includes the Polessie State Radioecology Reserve in Belarus, remains highly contaminated with ¹³⁷Cs to such an extent they remain uninhabitable. Whilst there is a broad scale understanding of the depositional patterns within and beyond the exclusion zone, detailed mapping of the distribution is often limited. New developments in mobile gamma spectrometry provide the opportunity to map the fallout of ¹³⁷Cs and begin to reconstruct the depositional environment and the long-term behaviour of ¹³⁷Cs in the environment. Here, full gamma spectrum analysis using algorithms based on the peak-valley ratio derived from Monte Carlo simulations are used to estimate the total ¹³⁷Cs deposition and its depth distribution in the soil. The results revealed a pattern of ¹³⁷Cs distribution consistent with the deposition occurring at a time of flooding, which is validated by review of satellite imagery acquired at similar times of the year. The results were also consistent with systematic burial of the fallout ¹³⁷Cs by annual flooding events. These results were validated by sediment cores collected along a transect across the flood plain. The true merit of the approach was confirmed by exposing new insights into the spatial distribution and long term fate of ¹³⁷Cs across the floodplain. Such systematic patterns of behaviour are likely to be fundamental to the understanding of the radioecological behaviour of ¹³⁷Cs whilst also providing a tracer for quantifying the ecological controls on sediment movement and deposition at a landscape scale.

Measurements of 106Ru in Sweden during the autumn 2017: Gamma-ray spectrometric measurements of air filters, precipitation and soil samples, and in situ gamma-ray spectrometry measurement

During the last days of September to the first days of October in 2017, a unique detection of ¹⁰⁶Ru was observed in air filters sampled at different locations in Sweden via the national air monitoring network. Furthermore, measurements of precipitation also showed the presence of ¹⁰⁶Ru. This initiated soil sampling and in situ gamma-ray spectrometry at one of the locations.

Excitation functions of proton- and deuteron-induced nuclear reactions on natural iridium for the production of 191Pt

We studied the excitation functions of residual radionuclides produced via proton and deuteron bombardment on natural iridium in the energy ranges of 30-15 MeV and 50-15 MeV, respectively. A conventional stacked-foil activation technique combined with HPGe γ-ray spectrometry was used to measure the excitation functions for ^{189, 191}Pt and ^{189, 190g, 192g, 194g}Ir radionuclide production. Theoretical thick target yields were estimated to be 172 MBq/µA h and 192 MBq/µA h via the ¹⁹³Ir(p,3n)¹⁹¹Pt reaction at 29.6-17.5 MeV and the ¹⁹³Ir(d,4n)¹⁹¹Pt reaction at 40.3-23.8 MeV, respectively. The feasibility of ¹⁹¹Pt production from an iridium target was discussed, and compared with previously reported methods for the production of ¹⁹¹Pt.

Evaluating a Bayesian modelling approach (INLA-SPDE) for environmental mapping

Understanding the uncertainty in spatial modelling of environmental variables is important because it provides the end-users with the reliability of the maps. Over the past decades, Bayesian statistics has been successfully used. However, the conventional simulation-based Markov Chain Monte Carlo (MCMC) approaches are often computationally intensive. In this study, the performance of a novel Bayesian inference approach called Integrated Nested Laplace Approximation with Stochastic Partial Differential Equation (INLA-SPDE) was evaluated using independent calibration and validation datasets of various skewed and non-skewed soil properties and was compared with a linear mixed model estimated by residual maximum likelihood (REML-LMM). It was found that INLA-SPDE was equivalent to REML-LMM in terms of the model performance and was similarly robust with sparse datasets (i.e. 40-60 samples). In comparison, INLA-SPDE was able to estimate the posterior marginal distributions of the model parameters without extensive simulations. It was concluded that INLA-SPDE had the potential to map the spatial distribution of environmental variables along with their posterior marginal distributions for environmental management. Some drawbacks were identified with INLA-SPDE, including artefacts of model response due to the use of triangle meshes and a longer computational time when dealing with non-Gaussian likelihood families.

Activity measurement of 222Rn gas for a key comparison

The Korea Research Institute of Standards and Science (KRISS) participated, in 2015, in an international Key Comparison (KC) of gaseous radon-222 activity named CCRI (II) -K2.Rn-222 to confirm international equivalence of KRISS-established gaseous radon-222 measurement standards. LNHB acted as KC pilot laboratory. This paper describes the KC measurement procedure followed at KRISS using the defined solid angle counting method together with auxiliary relative measurement methods and presents the results.