Gamma-ray Spectrometric Measurements Research Articles

Measurement function for the activities of multi-gamma-ray emitters in gamma-ray spectrometric measurements

In gamma-ray spectrometric measurements the background is usually taken into account by conducting measurements on a blank sample. However, this method is not appropriate if many different kinds of samples are measured and several types of detectors are used. In such cases it is easier to measure accurately the activities of the blank materials separately and then to subtract the activities of the blank sample from the total sample activities. In order to do this, the measurement function for the activity calculation must be modified.

Relationships between ground and airborne gamma-ray spectrometric survey data, North Ras Millan, Southern Sinai Peninsula, Egypt

In the last decades of years, there was considerable growth in the use of airborne gamma-ray spectrometry. With this growth, there was an increasing need to standardize airborne measurements, so that they can be independent of survey parameters. Acceptable procedures were developed for converting airborne to ground gamma-ray spectrometric measurements of total-count intensity as well as, potassium, equivalent uranium and equivalent thorium concentrations, due to natural sources of radiation.The present study aims mainly to establish relationships between ground and airborne gamma-ray spectrometric data, North Ras Millan, Southern Sinai Peninsula, Egypt. The relationships between airborne and ground gamma-ray spectrometric data were deduced for the original and separated rock units in the study area. Various rocks in the study area, represented by Quaternary Wadi sediments, Cambro-Ordovician sandstones, basic dykes and granites, are shown on the detailed geologic map. The structures are displayed, which located on the detailed geologic map, are compiled from the integration of previous geophysical and surface geological studies.

Application of gamma ray spectrometric measurements and VLF-EM data for tracing vein type uranium mineralization, El-Sela area, South Eastern Desert, Egypt

This study is an attempt to use the gamma ray spectrometric measurements and VLF-EM data to identify the subsurface structure and map uranium mineralization along El Sela shear zone, South Eastern Desert of Egypt. Many injections more or less mineralized with uranium and associated with alteration processes were recorded in El Sela shear zone. As results from previous works, the emplacement of these injections is structurally controlled and well defined by large shear zones striking in an ENE–WSW direction and crosscut by NW–SE to NNW–SSE fault sets. VLF method has been applied to map the structure and the presence of radioactive minerals that have been delineated by the detection of high uranium mineralization. The electromagnetic survey was carried out to detect the presence of shallow and deep conductive zones that cross the granites along ENE–WSW fracturing directions and to map its spatial distribution. The survey comprised seventy N–S spectrometry and VLF-EM profiles with 20m separation. The resulted data were displayed as composite maps for K, eU and eTh as well as VLF-Fraser map. Twelve profiles with 100m separation were selected for detailed description. The VLF-EM data were interpreted qualitatively as well as quantitatively using the Fraser and the Karous–Hjelt filters. Fraser filtered data and relative current density pseudo-sections indicate the presence of shallow and deep conductive zones that cross the granites along ENE–WSW shearing directions. High uranium concentrations found just above the higher apparent current-density zones that coincide with El-Sela shear zone indicate a positive relation between conductivity and uranium minerals occurrence. This enables to infer that the anomalies detected by VLF-EM data are due to the highly conductive shear zone enriched with uranium mineralization extending for more than 80m.

Analysis of radionuclide concentration in air released through the stack of a radiopharmaceutical production facility based on a medical cyclotron

Abstract Positron emitting radionuclides are increasingly used in medical diagnostics and the number of radiopharmaceutical production facilities have been estimated to be growing worldwide. During the process of production and/or patient administration of radiopharmaceuticals, an amount of these radionuclides might become airborne and escape into the environment. Therefore, the analysis of radionuclide concentration in the air released to the stack is a very important issue to evaluate the dose to the population living around the plant. To this end, sampling and measurement of radionuclide concentration in air released through the stack of a Nuclear Medicine Center (NMC), provided with a cyclotron for radiopharmaceuticals production, must be routinely carried out with an automatic measurement system. In this work is presented the air monitoring system realized at “San Gaetano” NMC at Bagheria (Italy) besides the analysis of the recorded stack relesead air concentration data. Sampling of air was carried out continuously and gamma-ray spectrometric measurement are made on-line and for a short time by using a shielded Marinelli beaker filled with sampled air and a gamma detector. The use of this system allows to have 1440 values of air concentration per day from 2002, year of the start of operation with the cyclotron. Therefore, the concentration values are very many and an analysis software is needed to determine the dose to the population. A comparison with the results of a simulation code based on a Gaussian Plume air dispersion modelling allow us to confirm the no-radiological significance of the stack effluent releases in terms of dose to population and to evaluate possible improvements in the plant devices to reduce the air concentration at stack.

Constraints on the abundance of carbon in near-surface materials on Mercury: Results from the MESSENGER Gamma-Ray Spectrometer

Mercury׳s low surface reflectance and the low surface abundances of iron and titanium have led to the suggestion that carbon (C) may serve as the dominant darkening agent on Mercury׳s surface. Estimates of the amount of carbon required to achieve the observed surface darkening are within the sensitivity range of measurements by MESSENGER׳s Gamma-Ray Spectrometer (GRS). We use GRS measurements to constrain the C content of Mercury׳s surface, the first such use of gamma-ray spectroscopy data. Our methodology includes techniques for removing background contributions to the measured signal and is broadly applicable to any gamma-ray spectroscopy dataset. The measured C content for Mercury׳s surface, 1.4±0.9wt%, is consistent with 0–4.1wt% C at the three-standard-deviation level and therefore does not represent a definitive detection of C at the surface. Possible mechanisms for providing up to 4.1wt% C on Mercury׳s surface include primordial and exogenous sources. Additional measurements at low altitude made with MESSENGER׳s Neutron Spectrometer can yield further constraints on the C content of Mercury׳s surface.

Analytical evaluation of natural radionuclides and their radioactive equilibrium in raw materials and by-products

An investigation into the distribution of natural radionuclides and radioactive secular equilibrium in raw materials and by-products in a domestic distribution was conducted to deduce the optimum conditions for the analytical evaluation of natural radionuclides for 238U, 226Ra, and 232Th using a gamma-ray spectrometer and inductively coupled plasma mass spectrometer (ICP-MS). The range of the specific activities of natural radionuclides was first evaluated by analyzing 228Ac and 214Bi, which are 232Th and 226Ra indicators, respectively, in about 100 samples of raw materials and by-products through a gamma-ray spectrometer. From further experiments using several samples selected based on the results of the distribution of natural radionuclides, the validation of their analytical evaluations for the indirect measurements using a gamma-ray spectrometer and direct measurements using ICP-MS was assured by comparing their results. Chemically processed products from the raw materials, such as Zr sand and ceramic balls, were generally shown for the type of bead and particularly analyzed showing a definite disequilibrium with above a 50% difference between 238U and 226Ra in the uranium series and 232Th and 228Ra in the thorium series.

Uncertainty of gamma-ray spectrometry measurement of environmental samples due to uncertainties in matrix composition, density and sample geometry

This paper is intended to identify the uncertainties of activities in environmental samples measured with gamma-ray spectrometry that result from uncertainties in matrix composition, density and geometrical dimensions of the sample. For that purpose efficiencies were calculated for a wide range of environmental matrices such as fresh and ashed food samples, water samples and soil samples. Compositions were mainly taken from literature. Densities and geometry parameters were varied in a range occurring in practice. Considered energies cover a range from 46.5keV to 2000keV. Finally, a couple of recommendations in respect to gamma-ray spectrometric measurements of environmental samples are given.

Calculation of the decision thresholds in gamma-ray spectrometry

A method was developed for calculating the decision thresholds for gamma-ray spectrometric measurements. At the energies where gamma-ray emitters that are present in the nuclide library, but were not identified in the spectrum, radiate, peaks are supposed to appear. The peak areas are calculated by fitting, using the method of least squares, the spectral region of the supposed peaks with a continuous background and the spectrometer response function at the gamma-ray energies where the supposed peaks are positioned. The null measurement uncertainty of a gamma-ray emitter is obtained as the uncertainty of the weighted average of the activities calculated from the areas of the supposed peaks in a spectrum where the specified activity of the gamma-ray emitter is zero. For the calculation of the decision threshold the null measurement uncertainty is used. These decision thresholds overestimate the critical limits calculated with the Currie formula by about 10% in the case of single gamma-ray emitters. For multi-gamma-ray emitters the decision thresholds yield smaller values than the Currie formula. The presence of a peaked background or peaks that are near the supposed peaks increases the decision threshold considerably.

Measurement of radionuclide activities induced in target components of an IBA CYCLONE 18/9 by gamma-ray spectrometry with HPGe and LaBr3: Ce detectors.

Cyclotrons are used worldwide to produce radiopharmaceuticals by proton irradiation of a suitable target. The intense secondary neutron beam generated by proton interactions with the target induce high radionuclide activities in the target assembly parts that may result in an exposure to high dose levels of the operators during maintenance. The main goal of this work is to evaluate gamma-emitting radionuclide activities induced in Havar foils and titanium windows of a target assembly and carousel stripper forks of an IBA CYCLONE 18/9 cyclotron. The knowledge of radionuclide inventory for each component is required by many companies to assess risk for operators before waste handling and disposal. Gamma-ray spectrometric analyses were carried out with High Purity Germanium (HPGe) and Lanthanum bromide (LaBr3:Ce) scintillation detectors. HPGe is the most used detector for its high energy resolution although it is more suitable for use in a laboratory. The use of LaBr3:Ce can be considered a viable option, particularly in realizing a portable spectrometric system to perform "on-site" measurements and a fast dose rate evaluation before the disposal of activated parts. Due to a high activity of target assembly components replaced after a typical irradiation cycle (about 5000 μAh integrated beam current), gamma-ray spectrometric measurements were performed at a large distance from the detector, even more than 100 cm, or by using a purposely realized Lead-walled collimator. The identification of some key-radionuclides allows to evaluate through simple formulations the dose rate behavior for each component as function of decay time from the last irradiation. The knowledge of the dose rate behavior is a significant piece of information to health physicists for waste handling with safety at work. For an Havar™ foil, the dose rate will be reduced to about 1/1,000 of the starting value after a decay period of approximately 4 y (about 1,500 d), with a relatively safety at product disposal work. For a longer time, only long-lived radionuclides (57)Co, (60)Co, and (54)Mn contribute to dose rate.

Reporting gamma-ray spectrometric measurement results near the natural limit: primary measurement results, best estimates calculated with the Bayesian posterior and best estimates calculated with the probability density distribution resembling shifting

When reporting best estimates as measurement results, systematic influences near the natural limit are introduced that originate not only in the possible inconsistency of the analytical procedure but also in the conversion of the primary measurement results to best estimates. It has been shown that the probability density distribution resembling shifting of values observed in the unfeasible region to the limit of the feasible range (the natural limit) introduces a smaller systematic influence than the Bayesian posterior, resembling censoring with repetition of the measurements that result in observed values in the unfeasible region. The drawback that the uncertainty intervals calculated with the Bayesian posterior do not encompass the natural limit and may not encompass the observed value, although it lies within the feasible region, is avoided by using the probability density distribution resembling shifting. Therefore, such best estimates introduce a smaller systematic influence into the measurement results and are better suited as inputs for subsequent analyses.

Analysis of Radioactivity Content in Sediment, Water and Fish Collected From Rajakkamangalam Estury of Kanyakumari District in Tamilnadu, India

The natural radioactivity due to Uranium, Thorium and Potassium in soil, and water contributes to the radiation dose received by human beings significantly. For assessing the environmental radiological impact to the public it is essential to evaluate the activity levels of these nuclides. Results of the gamma ray spectrometric measurements, carried out for natural radioactivity levels due to

Baseline Assessment of dose due to Natural Radionuclides in soils of coastal regions of Kanyakumari district in Tamil Nadu, India

The natural radioactivity due to uranium, Thorium and potassium in soil contributes to the radiation dose received by human beings significantly. Gamma ray spectrometric measurements carried out for the natural radioactivity levels due to 226 Ra, 232 Th and 40 K in beach sand samples around the coast of Kanyakumari district were analyzed. For assessing the environmental radiological impact to public it is essential to evaluate the activity levels of these radionuclides. The absorbed dose rate due to natural radionuclides was also calculated and the results are reported in this paper. The total annual effective dose of the study area founds to vary between 0.94 mSv to 2.23 mSv. This study provides a baseline data of radioactivity background levels in the coastal regions of Kanyakumari district from Muttom to Midalam and will be useful to assess any changes in the radioactive background levels.

Enhanced sodium abundance in Mercury’s north polar region revealed by the MESSENGER Gamma-Ray Spectrometer

MESSENGER Gamma-Ray Spectrometer measurements demonstrate that the abundance of Na varies across the surface of Mercury. The maximum Na/Si abundance ratio of 0.20±0.03 by weight (∼5wt% Na) is observed at high northern latitudes and is significantly larger than the equatorial Na/Si ratio of 0.11±0.01 (∼2.6wt% Na). Comparisons of forward-modeled surface distributions with the gamma-ray measurements suggest that the observed distribution of Na can be explained by differences in elemental composition between the volcanic smooth plains units and heavily cratered terrain. The comparison improves when thermally driven depletion of Na from areas near Mercury’s hot poles is included. When combined with other MESSENGER data sets, these results indicate that the smooth plains units include substantial abundances of alkali feldspars. Thermal depletion of Na from the hot poles without an assumed underlying compositional variability can also reproduce the measured Na/Si distribution, but that mechanism fails to account for other MESSENGER observations that support the presence of higher abundances of feldspars in the smooth plains units.

Uranium migration history in the igneous and metamorphic rocks of Solaf-Umm Takha area, based on multi-variate statistical analysis and favorability indices, central south Sinai, Egypt.

The present study deals with the application of three different analytical techniques on the recorded ground gamma ray spectrometric measurements in order to detect the radioelements content specially Uranium in Solaf-Umm Takha area, south Sinai, Egypt. These techniques include Uranium migration (in and out), Uranium favorability index and multi-variate statistical analysis including first and second principal component and factor scores. The obtained results have indicated that Umm Takha granite and the quartzo - feldspathic gneiss as well as the El-Sheikh granite are Uranium source rocks with low favorability indices. However the application of favorability index technique has proved to be an effective tool in igneous and metamorphic environments to indicate Uranium depletion from source rocks. The integration of original uranium content, uranium migration rate and Uranium favorability index indicated that Uranium migrated from the eastern and southern parts and has been ultimately accumulated in the western and northern parts of the study area. Topographically, uranium has been migrated from the high relief mountainous region to the drainage divide of Solaf-Umm Takha valleys. Therefore, uranium migration history proves its validity in distinction between syngentically-mineralized source rocks and secondary enriched rocks in the investigated area.

Gamma-ray spectrometric measurements of fission rate ratios between fresh and burnt fuel following irradiation in a zero-power reactor

The gamma-ray activity from short-lived fission products has been measured in fresh and burnt UO2 fuel samples after irradiation in a zero-power reactor. For the first time, short-lived gamma-ray activity from fresh and burnt fuel has been compared and fresh-to-burnt fuel fission rate ratios have been derived.For the measurements, well characterized fresh and burnt fuel samples, with burn-ups up to 46GWd/t, were irradiated in the zero-power research reactor PROTEUS. Fission rate ratios were derived based on the counting of high-energy gamma-rays above 2200keV, in order to discriminate against the high intrinsic activity of the burnt fuel.This paper presents the measured fresh-to-burnt fuel fission rate ratios based on the 142La (2542keV), 89Rb (2570keV), 138Cs (2640keV) and 95Y (3576keV) high-energy gamma-ray lines. Comparisons are made with the results of Monte Carlo modeling of the experimental configuration, carried out using the MCNPX code. The measured fission rate ratios have 1σ uncertainties of 1.7–3.4%. The comparisons with calculated predictions show an agreement within 1–3σ, although there appears to be a slight bias (∼3%).

Gamma-ray spectrometric measurement of radionuclide purity of radiopharmaceuticals contained in bottle samples

The radionuclide purity of a radiopharmaceutical product is usually measured by gamma-ray spectrometry with various measurement geometries. The importance of this test is that the radionuclide impurities, if present, result in an increase in the radiation dose to the patient without contributing to diagnostic information and in some cases may also interfere with the marking molecules and affect the proper conduct of diagnostic examination. In this work, gamma-ray spectrometry is used to determine the amounts of impurities by adopting as measurement geometry the same bottle containing eluted or prepared radiopharmaceuticals. In addition to high-purity germanium semiconductor detectors, the usefulness of NaI(Tl) and LaBr3(Ce) scintillators in routine operation is also examined. For the latter detectors, an evaluation of the minimum detectable activity was carried out and compared with the activity limits established by the regulation rules. The main cases considered are related to the first elution of 99Mo-99mTc generators and samples of 18F-FDG (fluoro-deoxy-glucose) to be used for positron emission tomography diagnostics.

Natural radionuclide distribution in quartzite sands of East Mediterranean Region (Turkey)

The study examined 15 sites in the Ovacik-Kargicak (Mersin, Turkey) open pit mines and obtained two quartzite samples from each. Gamma-ray spectrometric measurements were undertaken on the quartzite rocks and sands to quantify the concentrations of the natural radionuclides 226Ra, 232Th and 40K. In addition, the mean radioactivity concentrations of these natural nuclides were calculated to be 6.94, 7.34 and 140.05 Bqkg−1. Also the mean radioactivity concentrations of the natural nuclides in old Ovacik quartzite sands 226Ra, 232Th and 40K were calculated to be 9.85, 10.54, and 226.40 Bqkg−1, respectively.

Probability for Type I errors in gamma-ray spectrometric measurements of drinking water samples

In gamma-ray spectra, acquired in the absence of the sample, peaks occur which belong to the spectrometer background. When samples are measured, which contain radionuclides that appear in the background also and have activities near the detection level, the background contributes substantially to the peak areas. In the extreme case, when the contribution of the sample is much smaller than the contribution of the background, the peak area attributed to the radionuclide within a sample has the same probability of being positive or negative. Therefore, to interpret the results obtained from measurements of low-activity samples, the performance of the spectrum analysis procedure near the detection level must be known. To test the performance of the spectrum analysis procedure at low activities, the spectrometer background spectra were analyzed as if they had been water samples, prepared as dry residue obtained by evaporation of 50 L of water. The probabilities for false positives together with their decision thresholds are given for radionuclides appearing in the background spectra. For some of the radionuclides that do not appear in the background spectra, probabilities for false detection are given as well.

Environmental gamma dosimetry with OSL of -Al2O3:C for in situ sediment measurements

The physical properties of alpha-Al(2)O(3):C are very similar to that of quartz, which make it an attractive dosimetric material for geological and archaeological dating applications. Storage experiments in an ultra-low-radiation underground environment (UDO at PTB) and gamma-ray spectrometry show that the optically stimulated luminescence (OSL) signal of this material does neither suffer from a significant inherent background caused by traces of radionuclides (<6 microGy a(-1)) nor from fading. After having performed a simple calibration procedure, gamma dosimetry based on alpha-Al(2)O(3):C detectors, which were exposed in a brick block and a lead castle for different periods of time, provided concordant results with dose values derived from independent gamma-ray spectrometric measurements using high-purity germanium and NaI:Tl detectors. These investigations indirectly confirm both the absence of a significant inherent background and fading of the detector material. Small doses of a few micro gray accumulated in short exposure times to environmental radiation can be accurately measured, even when doses (i.e. transport dose) much larger than the actual environmental dose have to be subtracted. It is shown that the OSL signal caused by small transport doses can be easily and reproducibly reset even under difficult field conditions by illuminating the dosemeters with the blue light from Luxeon LEDs. Summarised, alpha-Al(2)O(3):C appears to be the material of choice for dosimetric dating applications of quartz or related materials, when analysed by using OSL.

Integration of space images and airborne radiometric data for discrimination of radioactive mineralizations at Wadi Araba area, North Eastern Desert, Egypt

This research aims at integrating airborne gamma-ray spectrometric and remote sensing satellite data to appointment radioactivity of the rocks at Wadi Araba, which is located in the North Eastern Desert of Egypt. Airborne gamma-ray spectrometric data of the ore as well as construction of lithological and structural maps from Landsat ETM + image are used to achieve the present study. The processing of airborne gamma-ray spectrometric data covering the area produced maps that showed the distribution and intensities of (eU), (eTh) and ( 40K%). These maps were correlated with lithologic and structural maps, which were interpreted from Landsat ETM + image, to show the probably hosting zones of radioactive materials. This study is based on the differences of radiometric data, brightness Digital Number (DNs) values of the rocks, predominant trends and densities of the structural lineaments, shape and type of weathering products. The study area is divided into nine lithologic units according to the physical characteristic differences as well as gamma-ray spectrometer measurements to reveal the mineralized units and zones as well as the best conditions for exploration of radioactive materials. These studies recorded some uranium anomalies distributed along NE-SW trending fault zones. These occurrences are hosted in Rod El-Hamal, El Galala and Duwi Formations. The gamma-ray spectrometer measurements for some representative zones indicate the presence of eU up to 20 ppm in the northeast direction and exceeding more than 35 ppm along zones fault cutting G. El Galala El Bahariya and G. El Galala El Qibliya. The characteristic features responsible for the uranium mineralization are the high fracture density of the Rod El-Hamal, Sudr and Duwi Formations. These fractures acted as good channels for hydrothermal ascending fluids and/or the percolating meteoric water. The hematitization accompanied these zones leached uranium which is redeposited and adsorbed onto hematite especially at the sites of intersection of the main fractures. The study shows that integrated application of satellite remote sensing techniques and airborne processed data is a powerful tool in the exploration of radioactive materials.