The masses of thin, electroplated deposits of 235U, 238U and 239Pu on titanium backings have been determined to better than 1.3% precision by employing three complementary measurement techniques: α ...spectrometry, 2π gas counting, and γ-ray spectrometry. A dedicated α spectrometer was designed and calibrated to allow for repeatable, high-precision measurements of the absolute α activity of a sample. The isotopic composition of the sample was determined by fitting the peaks in the α spectrum, a technique which was demonstrated to be generally consistent with mass spectrometry. Independently, the total activity of the deposits were measured in a 2π gas flow proportional counter. A detailed study of the effects of α particle straggling in the actinide deposit and α particle recoil off the sample backing material was performed. The masses of these actinide deposits were also measured via γ-ray spectrometry. We found that all three systematically independent techniques produced consistent results, and could be combined into a weighted average with further reduced uncertainty. The mass ratios of these actinide deposits were determined to better than 1% precision via α spectrometry, enabling high-precision fission cross section ratio measurements.
Multidimensional gamma-spectrometry is a potential solution for safeguarding future thorium-fuelled molten salt reactors (MSRs). A high-sensitivity system developed at Pacific Northwest National ...Laboratory (PNNL), the Advanced Radionuclide Gamma spectrometer (ARGO), has demonstrated direct 233U assay in freshly irradiated fuel salt samples using a dual-detector configuration and the 97.1 keV gamma-emission. These measurements were made using 1.4 × 106 Bq of 233U activity (at 1.4 × 108 fissions), at relatively high dead times (10.4%), and using short count durations of ∼800 s. Other major emissions were also evaluated (42.5 keV, 54.7 keV, 146.4 keV), in additional to limited (1.96%) Compton suppression, but provided less consistent determination of the 233U activity. Accurate 233U measurement was also demonstrated using its four-coincidence gamma-emissions (42.5 keV, 54.7 keV; 42.5 keV, 278.1 keV; 146.4 keV, 174.2 keV; 146.4 keV, 219 keV). Further improvements in coincidence measurements may be achievable with improvements in the detector configuration and nuclear data. Whilst this demonstration utilized the ARGO laboratory system, a similar dual-detector configuration could be utilized for online safeguards measurements.
The MCNP code was utilized to assess the operational status of an N-type high-purity germanium (HPGe) detector and to evaluate its potential for a collimated and focused Prompt Gamma Neutron ...Activation Analysis (PGNAA) detection system. In order to calibrate the detector, a narrow beam γ collimator was designed to scan the detector in both axial and radial directions. The curvature of the crystal front edge and the non-uniform description of the detector dead layer (DL) were taken into account when adjusting the effective crystal size. A collimated 137Cs γ source was used to assess the detection efficiency in the scanning experiments. Monte Carlo studies were performed using 0.662 MeV γ rays, and separately, a uniform γ-ray energy distribution from 0 to 1.6 MeV. Lastly, the effects of a collimation aperture with different sizes and different incident directions were considered to discuss the relationship between the spatial resolution and suitable measurement scenarios. Therefore, a detailed calibration method for non-uniform dead layers was introduced through a comparison between experiments and Monte Carlo simulations. This work reevaluates the performance of HPGe detectors and provides valuable data support for a detailed system design and γ spectroscopy analysis in future.
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.
•Origin of background events in the low-level gamma spectroscopy is described.•Passive and active shielding designed for environmental samples measurement are explored.•Detection limit without and with presence of environmental sample is considered.•Sample geometry and detection efficiencies are analyzed.•Analysis of activity concentrations of environmental samples is discussed.
The aim of this study was to obtain a relationship that can estimate the emission pattern of 232Th in calm and low pressure aquatic environments such as Gorgan Bay. The 232Th emission pattern in ...sediments near the outlets of Gaz and Qarasu rivers using experimental data measured by gamma radiation spectrometry using high purity germanium (HPGe) detector and quasi-experimental model recommended by IAEA 2001 as well as the concentric circular diffusion model proposed by authors was investigated. The mean specific activity of 232Th in sediment samples for Gaz Block and Qarasu Block is 30.46 Bqkg−1 and 28.80 Bqkg−1 for, respectively.
In Gaz Block, for model1: the average of CsModel1 was 29.03 Bqkg−1 and the mean relative error is 10.76%. For model2: the average of CsModel2 was 30.34 Bqkg−1 and the mean relative error is 7.58%.
In Qarasu Block, for model1: the average of CsModel1 was 27.48 Bqkg−1 and the mean relative error is 12.08%. For model2: the average of CsModel2 was 34.17 Bqkg−1 and the mean relative error is 38.99%.
The results of this research show that diffusion models 1 and 2 in the calm environment of Gorgan Bay can accurately predict 232Th diffusion. But as increase the amount of turbulence and interference effects in the environment, the accuracy of these two models decreases. These two models can be used in similar calm aquatic environments in other parts of the world.
•Experimental measurement of Thorium activity in sediment samples of Gorgan Bay.•Calculating the thorium distribution in Bay environ.•Using GIS software for diffusion pattern in Bay Environ.•Results Showed good agreements between two model of calculation and experimental results.
The masses of thin, electroplated deposits of 235U, 238U and 239Pu on titanium backings have been determined to better than 1.3% precision by employing three complementary measurement techniques: ...$\alpha$ spectrometry, 2$\pi$ gas counting, and $\gamma$-ray spectrometry. A dedicated $\alpha$ spectrometer was designed and calibrated to allow for repeatable, high-precision measurements of the absolute $\alpha$ activity of a sample. The isotopic composition of the sample was determined by fitting the peaks in the $\alpha$ spectrum, a technique which was demonstrated to be generally consistent with mass spectrometry. Independently, the total activity of the deposits were measured in a 2$\pi$ gas flow proportional counter. A detailed study of the effects of $\alpha$ particle straggling in the actinide deposit and $\alpha$ particle recoil off the sample backing material was performed. The masses of these actinide deposits were also measured via $\gamma$-ray spectrometry. Here, we found that all three systematically independent techniques produced consistent results, and could be combined into a weighted average with further reduced uncertainty. The mass ratios of these actinide deposits were determined to better than 1% precision via $\alpha$ spectrometry, enabling high-precision fission cross section ratio measurements.
Due to the Chernobyl nuclear power plant accident, contaminated air masses, containing 137Cs, were widely propagated across all of Europe. Cesium-137 is easily adsorbed on aerosol particles as it ...returns to the lithosphere/pedosphere/via wet and dry deposition in the form of a radioactive fallout component. Following the nuclear accident, primary attention was paid to agricultural areas and less to urban environments. Our 137Cs activity study using undisturbed attic dust samples has been carried out from two residential areas (city of Salgótarján and Ózd) in northern Hungary, approx. 1000 km away from Chernobyl. A total of 61 attic dust samples were collected in 2016 and 2018 from houses (>30 years) functioning as family house, kindergarten, blockhouse and church. Activity concentration of 137Cs was determined for 1–2 g homogenized (<125 μm) attic dust samples in a low background iron chamber with a well-type HPGe detector. The mean 137Cs activity concentrations in attic dust samples are 88.5 ± 5.1 Bq kg−1 and 87.8 ± 4.5 Bq kg−1 in Salgótarján and Ózd, respectively. The dependence between 137Cs activities and the age of the houses was found to be significant (p=0.02), which could be explained by Chernobyl nuclear accident-causing elevated activity concentrations in location built prior to the accident. Three outliers in Ózd (>223 Bq kg−1), are probably related to the first rainfall event after the Chernobyl accident. Isotopic landscapes (isoscapes) of 137Cs were derived for both cities by means of kriging interpolation. In Salgótarján the 137Cs activity concentrations were higher than in Ózd which might have been due to redistribution loadings and local topographical features. We concluded that components of attic dust are highly useful indicators of home exposure to pollution events and remain detectable after several decades.
•The long-term accumulation of dust preserves high activity concentration of 137Cs in attic area.•The 137Cs activity concentration in >10% of the attic dust samples exceeded 100 Bq kg−1, reaches up to 272 Bq kg−1.•The meteorological simulations illustrated obvious differences in 137Cs deposition in the studied two cities.•Geostatistical analysis for pre-1950 built houses prove influence of topographical feature in 137Cs deposition rate.
