Mass attenuation coefficients of soil and sediment samples using gamma energies from 46.5 to 1332 keV

Low-level gamma ray counting on environmental samples

One of the major demands in gamma spectrometry of environmental samples is the accurate determination of activity concentration of present radionuclides (naturally occurring and those of artificial origin), due to the fact they are commonly of relatively low content. Thus, all these measurements have in common that the detection limit, in the spectral region of interest should be as low as possible. For this reason, the construction of a good passive, as well as active shield requires a detailed knowledge of the origin of the background events in the absence of an environmental sample. In addition, an analysis of the impact on detection limits due to the presence of the sample itself is also important. Also, the knowledge of the statistical basics for low-level counting is helpful to enable the best choice of detector characteristics (relative efficiency, peak to Compton ratio, resolution), measuring time, and required level of precaution against the different background contributions. In this paper, the background spectra of several gamma spectroscopy systems (with passive and active veto shields) are analyzed and discussed, regarding their capabilities for measurements of environmental samples. Furthermore, various environmental samples are analyzed by low-level gamma spectrometry, including the sample measurements in the presence of an active veto shield against cosmic-ray muons. The disturbance of radioactive equilibrium between members of radioactive series in the samples is commented on, together with the possibility of use of certain gamma lines (including their interference and the corresponding intensities) for radionuclide activities determination.

Insights into the Effect of Aggregate Sizes on the Soil Radiation Interaction Properties Based on X-ray Fluorescence

Soils subjected to disaggregation can break into aggregates of different sizes composed of sand, clay, and silt particles. Each aggregate contains different oxides, which can vary according to the aggregate size and influence its properties, such as the radiation interaction parameters. These parameters are relevant in the evaluation of radiation shielding and soil physical properties. Thirteen tropical/subtropical soils of contrasting textures (clayey and loamy/sandy) with two aggregate sizes (2-1 mm and <45 μm) were studied. The radiation parameters analyzed were the atomic (σ_A), electronic (σ_E), and molecular (σ_M) cross-sections; the effective atomic number (Z_eff); and the electron density (N_el). We verified that the aggregate sizes affected the major oxides (SiO₂, Al₂O₃, Fe₂O₃). In general, the attenuation coefficient and Z_eff were sensitive to the clayey soils' aggregate sizes (low photon energies). However, the loamy/sandy soils did not exhibit differences among the parameters. As the photon energy increased, only Z_eff presented differences for most soils. We also verified that σ_M, Z_eff, and N_el were the most sensitive parameters to the soil composition. Although the soil chemical composition was influenced by the studied aggregate sizes, the radiation parameters exhibited differences for only some of these parameters. This means that the aggregate size is practically irrelevant when radiation parameters are determined based on X-ray fluorescence.

X-ray radiation monitor for measuring solids content in fluid fine tailings

The extraction of bitumen from oil sands produces fluid fine tailings (FFT) consisting mainly of water, sands, clay, and residual bitumen. Generally, devices with radioactive sources are used to measure the variation of FFT density or solids concentration inline, but to date there is no suitable device for in situ monitoring in tailings storage facilities such as large tailings ponds. In this study, an alternative method using high-resolution spectrometry based on a low radiation intensity source and a cadmium telluride (CdTe) detector was used to measure the solids content in tailings samples based on X-ray attenuation. The radiation source used in the experiment was a 1 μCi ¹³³ Ba. GEANT4, a Monte Carlo-based simulation code that calculates the transmission of radiation through matter, was used to simulate the results of this study and build calibration curves that can determine the solids content concentration based on measured sample composition. Experiments and simulations were performed on various concentrations of both actual FFT samples from tailings facilities and kaolin as a model material. Good agreement between the experimental and simulation results was observed, paving the way for a potential real-time solids content measurement system that could be deployed over large areas to measure the settling of FFT in tailings ponds.

A practical approach to determining soil-sample detection efficiency in field gamma-ray spectroscopy

Field measurements of radionuclide activities in soil samples via gamma spectroscopy measurements are conducted for many applications. One example application space is on-site inspection for the Comprehensive Nuclear-Test-Ban Treaty. To extract isotopic activities from observed peak counting rates, it is necessary to understand the absolute efficiency of the detector system for a sample. In principle, this efficiency is a function of many parameters, such as sample geometry, soil elemental composition, and soil density. The demands of field measurements within the context of on-site inspections, however, places a premium on an easy-to-implement approach at the possible expense of accuracy given the need to process many samples in a short period of time. This paper presents a semi-empirical approach, using a calibrated standard and a correction that depends only on the relative differences in density of the sample and the standard. Field measurements were conducted to demonstrate the validity of the approach.

Self-attenuation corrections for radium measurements of oil and gas solids by gamma spectroscopy

Beneficial reuse and resource recovery of produced water often require treatment to remove radium before valuable products are extracted. The radium content of the treatment waste solids and beneficial products must be accurately determined when evaluating the efficacy and social validity of such treatments. While gamma spectroscopy remains the recommended method for radium measurements, these measurements can be impacted by the composition/mineralogy of the solids, which influence the attenuation of the gamma decay energy - with denser sediments incurring greater degrees of attenuation. This self-attenuation must be accounted for when accurately measuring radium, otherwise radium measurements are found to be inaccurate, sometimes by as much as 50%. To meet industry needs, measurements should be both accurate and rapid, even for small sample sizes. Consequently, we propose a rapid method for accurate radium measurements with an empirical technique to account for sample attenuation in well-detector gamma spectroscopy. This technique utilizes the sample density and sample volume in the measuring vial. These corrections are relevant to a wide range of solid samples and sediment densities that may be encountered during treatment and management of oil and gas solids, including clays, environmental sediment samples, sand grains, and precipitated salts. These corrections can also be applied for situations were low volumes of material are present, as in bench scale studies, thereby rendering this technique applicable to a wider range of scenarios.

Evaluation of radiation absorption capacity of some soil samples

The aim of the present work is to investigate the radiation absorption capacity of different soil samples in Turkey. For this purpose, we used a γ ray transmission geometry to measure the mass attenuation coefficients of eight soil samples collected between Bingöl city and Solhan district, Turkey at different γ-ray energies in the range of 13.94–88.04 keV. The radioactive sources utilized in the experiment were 241Am, 109Cd and 133Ba. FFAST and WinXCOM programs were used to evaluate the theoretical mass attenuation coefficients values of the selected soil samples. There is a good agreement between experimental and theoretical results. Additionally, the mass attenuation coefficients values used to evaluate different radiation shielding parameters such as effective atomic number, half value layer and mean free path. The variation of shielding parameters was examined for soil composition and photon energy. The obtained results revealed that S6 soil sample is the best soil in terms of shielding effectiveness among all the collected soils due to lower values for half value layer and mean free path. The effective removal cross-section (Σ R ) of fast neutrons for the collected soils was also computed to examine neutrons shielding properties of the soil samples. It is found that the Σ R values for the soil samples are almost constant and lie within the range (0.04286–0.04949 cm−1).

Study of a remediated coal ash depository from a radiological perspective

Coal-fired power plants play a significant role in the production of electricity. The Ra-226 concentration of coals mined in the Ajka region can reach up to 3000 Bq/kg. This study focuses on the effects of a Hungarian (Ajka) remediated coal ash depository on the environment and the effectiveness of the cover layer. During the remediation, a method patented in Hungary was used, in which the upper layer of the depository, which had settled like concrete, was ploughed and mixed with woodchips before being planted with vegetation. The gamma dose rate H*(10) of the depository and its vicinity was measured using Automess 6150AD-b at 32 points, surface Rn-222 exhalation at 19 points and air radon concentration at 34 points; at 32 points, soil gas radon content was measured with AlphaGUARD and soil permeability with RADON-JOK. The nuclide content of nine samples was determined using an HPGe gamma spectrometer and their Rn-222 exhalation rates were measured using the AlphaGUARD. H*(10) was 290 (130-525) nSv/h at the covered depository; C_Ra-226 was 1997 Bq/kg, 960 Bq/kg and 104 Bq/kg for the ash, cover layer and background soil respectively. C_Rn-222 in the soil was 25-161 kBq/m³, and soil gas permeability K was between 6.4E-13 and 1.80E-11 m². The radon exhalation of the uncovered and covered depository was 259-1100 mBq/m²s. The exhalation and emanation coefficients of the samples were 0.05-0.32 mBq/kgs and 8-22%. The effects of vegetation on the migration of radon were also examined. The results show that the Ajka coal ash depository involves higher radiological risk than that reported by previously published studies on depositories. The applied cover layer halved the field radon exhalation; in addition, the vegetation reduced the convective airflow and, with this, the migration of Rn.

Determination of self-attenuation correction factor for lichen samples by using gamma-ray spectrometry

In this study, we determine the self attenuation correction factor for lichen samples collected from Erzurum, a city located in the eastern region of Turkey by using gamma-ray spectrometry. The self attenuation correction factor is calculated for 17 lichen samples with densities ranging from 0.683 g/cm3 to 0.886 g/cm3. The transmission method has been used to obtain self-attenuation correction factors. Self attenuation correction factor versus energy fit curve is presented. It is observed that self attenuation correction factor changes with density. At lower energies the self-attenuation correction factor has higher values. At higher energies it has smaller values and tends to become stable.

Fast self-attenuation determination of low energy gamma lines

Linear correlation between self-attenuation factor of 46.5keV ((210)Pb) and the 1764keV, 46.5 counts ratio has been developed in this work using triple superphosphate fertilizer samples. Similar correlation has been also developed for 63.3keV ((238)U). This correlation offers simple, fast, and accurate technique for self-attenuation determination of low energy gamma lines. Utilization of 46.5keV in the ratio has remarkably improved the technique sensitivity in comparison with other work, which used similar concept. The obtained results were used to assess the validity of transmission technique.

Determination of activity concentration of natural and artificial radionuclides in sand samples from mediterranean coast of Antalya in Turkey

In this paper, we attempt to determine the activity concentration of natural and artificial radionuclides in 37 sand samples from the Mediterranean coast of Antalya in Turkey by using a high purity Germanium (HpGe) detector. 238U, 232Th, 40K and 137Cs activity concentrations, absorbed dose rate, annual effective dose equivalent, radium equivalent activity, external and internal hazard index of sand samples are determined res-pectively. The average values are 13.43 ± 0.21 Bq/kg, 6.96 ± 0.06 Bq/kg and, 122.46 ± 18.58 Bq/kg, for 238U, 232Th and 40K respectively. Most of the activity concentration values are less than below minimum detection limit for 137Cs. The average values of the absorbed dose rate D (nGy/h), annual effective dose equivalent AEDE(μSv/y), radium equivalent activity Raeq (Bq/kg), external hazard index Hex and internal hazard index Hin are 15.52 nGy/h, 19.03 μSv/y, 32.81 Bq/kg, 0.09 and 0.12 respectively. It is observed that 238U, 232Th, 40K and 137Cs activity concentrations, absorbed dose rate, annual effective dose equivalent, radium equivalent activity are in the limit of the published values, external and internal hazard index values are less than unity.