Gamma Spectrometry System Research Articles

Assessment of the calibration of gamma spectrometry systems in forest environments

A Monte Carlo simulation was used to develop a model of the response of a portable gamma spectrometry system in forest environments. This model was used to evaluate any corrections needed to measurements of 137Cs activity per unit area calibrated assuming an open field geometry. These were shown to be less than 20% for most forest environments. The model was also used to assess the impact of activity in the canopy on ground level measurements. For similar activity per unit area in the lower parts of the canopy as on the ground, 10-25% of the ground based measurement would be due to activity in the canopy, depending on the depth profile in the soil. The model verifies that an optional collimator cap can assess activity in the canopy by repeat survey.

Design and implementation of a mobile gamma spectrometry system to in vivo measure the accumulated activity of 131I in patients with thyroid diseases

The design and implementation of a mobile gamma spectrometry system to in vivo measure the accumulated activity of 131I in whole body and thyroid of patients with thyroid diseases are presented in this work. This system may be used for both pre-therapeutic and post-therapeutic dosimetry calculations. It consists of a detector and a movable support that allows its movement from one place to another.

INVESTIGATION OF NATURAL RADIOACTIVITY AS A POSSIBLE DRIVER OF CANCER INCIDENCE IN PARAÍBA, NORTHEASTERN BRAZIL.

An increase of health problems has been reported in the city of Triunfo, Paraíba, NE Brazil. This pattern has been attributed to environmental radiation since there are uranium deposits in the neighboring municipalities. The present study aimed to carry a radiometric survey in Triunfo to determine effective dose from external outdoor radiation exposure. The results were obtained through 'in situ' measurements using a gamma spectrometry system. The results ranged from 0.06 to 0.38 mSv/y, mean of 0.20 mSv/y. Due to the low value of the effective dose rate, we concluded that the area is characterized by low background radiation. Therefore, natural radioactivity is probably not directly influencing the increase in cancer incidence in the region. However, there is a need for complementary studies in this area to evaluate the dose from potential exposure to ingested and inhaled natural radionuclides from natural radioactivity in soil, rocks, vegetation and water.

Activity concentrations and dose assessment of 226Ra, 228Ra, 232Th, 40K , 222Rn and 220Rn in soil samples from Newmont-Akyem gold mine using gamma-ray spectrometry

In this study 14 soil samples were measured for natural radioactivity levels including radon-222 (222Rn) and radon-220 (220Rn) concentration at Akyem-Gold Mine premises, surrounding communities in Ghana. Both radon and radioactivity concentrations of radium-226 (226Ra), thorium-232 (232Th) and potassium-40 (40K) were determined by means of gamma spectrometry system equipped with high purity germanium detector. The studied samples gave natural radioactivity levels of 28, 12 and 11 Bq/kg, respectively compared to global 226Ra, 232Th, and 40K concentrations of 37, 33 and 400 Bq/kg, respectively, according to UNSCEAR (2000) report. The annual effective dose rate (AED) due to external and internal gamma exposure ranged from 0.060 to 0.18 mSvy-1 with a mean value of 0.11 ± 0.03 mSvy-1 compared to the recommended value of 1 mSvy-1. There is a correlation between 226Ra and 222Rn in soil gas with a good linear coefficient of (R2 =1). The availability of 226Ra and 222Rn shows that there is a source of uranium-238 (238U) and thorium-232 (232Th) bearing minerals within the adjacent geologic units of Akyem. This implies that most of the radon in the soil gas comes from 226Ra. The assessment of radium equivalent activity varied from 19.71 to 69.88 Bq/kg with mean value of 37.53 ± 15.51 Bq/kg lower than the global limit of 370 Bq/kg. The internal hazard index ranged from 0.07 to 0.25 Bq/Kg with a mean value of 0.13 ± 0.05 Bq/Kg, also lower than the accepted value of unity, while external hazard index ranged from 0.05 to 0.19 Bq/Kg with a mean value of 0.10 ± 0.04 Bq/Kg. Key words: Radon, thoron, natural radioactivity, annual effective dose, radium equivalent index, external and internal hazard index.

Measurement of Gamma Emitting Radionuclides in Environmental Samples of Talagang Tehsil-District Chakwal

Due to constant exposure of Human beings to radiation caused by terrestrial, extra-terrestrial and anthropogenic radio nuclides, it is necessary to determine/estimate the activity of various radio nuclides in environmental media such as vegetation, soil, and water. In the present research, the activities of 226Ra, 232Th and 40K are measured in soil, vegetation and water samples, collected from Talagang Tehsil-District Chakwal of Pakistan using a HPGe based gamma spectrometry system. The measured mean activity of 226Ra, 232Th and 40K in soil samples was found to be 31.19±1.2, 47.00±2.30 and 589.31±17.52 Bqkg-1, respectively. The measured mean activity of these radionuclides in all water samples was found to be below minimum detectable activity. The measured mean activity of 226Ra, 232Th and 40K in vegetation samples was 19.92±3.09, 25.36±8.11 and 4982.94±85.68 Bqkg-1, respectively. No anthropogenic 137Cs was detected in these environmental samples. Mean radium equivalent activity (Raeq), external radiation hazard index (Hex), internal radiation hazard index (Hin) and absorbed dose rate (D) for the area under study were determined as 142.92 Bqkg-1, 0.38, 0.47 and 66.47 nGyh-1, respectively. The annual effective dose equivalent (AEDE) varied in the range from 0.03 to 0.12 mSv y-1. It is concluded that the surveyed area do not pose any significant radiological risk to the population and environment.

Theoretical determination of gamma spectrometry systems efficiency based on probability functions. Application to self-attenuation correction factors

A generic theoretical methodology for the calculation of the efficiency of gamma spectrometry systems is introduced in this work. The procedure is valid for any type of source and detector and can be applied to determine the full energy peak and the total efficiency of any source-detector system. The methodology is based on the idea of underlying probability of detection, which describes the physical model for the detection of the gamma radiation at the particular studied situation. This probability depends explicitly on the direction of the gamma radiation, allowing the use of this dependence the development of more realistic and complex models than the traditional models based on the point source integration. The probability function that has to be employed in practice must reproduce the relevant characteristics of the detection process occurring at the particular studied situation. Once the probability is defined, the efficiency calculations can be performed in general by using numerical methods. Monte Carlo integration procedure is especially useful to perform the calculations when complex probability functions are used. The methodology can be used for the direct determination of the efficiency and also for the calculation of corrections that require this determination of the efficiency, as it is the case of coincidence summing, geometric or self-attenuation corrections. In particular, we have applied the procedure to obtain some of the classical self-attenuation correction factors usually employed to correct for the sample attenuation of cylindrical geometry sources. The methodology clarifies the theoretical basis and approximations associated to each factor, by making explicit the probability which is generally hidden and implicit to each model. It has been shown that most of these self-attenuation correction factors can be derived by using a common underlying probability, having this probability a growing level of complexity as it reproduces more precisely the geometric and attenuation configuration of the source-detector system. Experimental verification of the improvement produced by increasing the model complexity has been performed by measuring samples spiked with certified nuclide activities with a HPGe detector. The methodology can be extended to obtain the theoretical efficiencies and corrections corresponding to any geometry by defining adequately the physical model and the subsequent probability corresponding to the particular studied situation.

Experimental Investigation on the Photopeak Efficiency of a Coaxial High Purity Germanium Detector for Different Geometries

Purpose: Gamma spectrometer systems are complex instruments, and the quality of the numerical results they provide strongly depends on their reliable calibration. In this study, it was aimed to determine the full-energy peak efficiencies of a 40% p-type High Purity Germanium HPGe detector for point source, Marinelli beaker, and cylindrical container geometries in the 200-1500 keV energy range. Methods: The efficiency calibration of the HPGe gamma spectrometry system was performed using certified calibration sources. Efficiency values were determined using the gamma ray spectrum acquired for every calibration source.Results: Two different efficiency curves, at the linear scale and logarithmic scale-fitting, experimental efficiencies were plotted. The functions and parameters that fitted the efficiency curves were obtained by a computer program.Conclusion: The photopeak efficiencies decrease as energy increases and the observed efficiency curves were closely with similar studies

Determination of Natural Radioactivity in the North East Beach Sands of Madagascar

Exploration and exploitation of radioactive ores (ilmenite, zircon and monazite) are considered as the main source of exposure to ionizing radiation of the population living in the coast of Analanjorofo Region (Fenerive-Est Districts, Rural municipality Ampasimbe Manantsatrana). Radioactivity measurements have been performed in this region. The distribution of natural radionuclide gamma-emitters (238U, 232Th and 40K) and their respective annual effective dose rates have been determined for sand(s), water and air. The samples have been collected along and around the coast of the region. The radiation emitted from the natural radionuclide containing in the environmental samples has been determined by gamma spectrometry system and Radon meter (SARAD). Exposure dose rates at 1 m above the ground have been measured along the coast and in the villages around the exploitation sites. Dose rate measurements have been performed by Dosimeter Graetz X5 DE, equipped of Geiger Muller Counter. Results have been compared with the reference values provided by IAEA (BSS 115) and UNSCEAR 2000.

The Radiological Contamination in AL-Tahreer Tower Building at Baghdad City

In this study, evaluation of the radioactivity for AL-Tahreer Tower Building (the Turkish restaurant previously) which located in the center of Baghdad city was implemented. The contamination resulted from bombing the Building by the depleted uranium projectiles. The building consists of 14 floors besides the basement. Radiological characterization was implemented using field and laboratory measurements. The results of radiological surveys by using portable survey meter (CAB-counts per second (cps)) indicated the presence of contaminated soil reached to 60 cps (more than 120 the background radiation level) in addition to the presence of small particles of depleted uranium shells with high levels of contamination reached to 90 cps, compare with (0.5 cps) the background level. While the results of maximum exposure dose rates were 0.6 µSv/hr when the detector of survey meter (Ludlum) put on the contaminated regions at a distance about (0.5 cm). The natural background level of the building at distance one meter was 0.9 µSv/hr. Soil samples had been collected and prepared for measuring according to the international standards and specifications, using gamma spectrometry system which consist of High-purity Germanium Detector with efficiency of 40% and resolution 2.0 keV for Energy 1.332 MeV of ⁶⁰Co, The laboratory results indicated the presence of high concentrations of Th-234 and Pa-234m isotopes (1550.1 & 3179 Bq/kg respectively) in the soil samples taken from the floors, while the concentrations of Th-234 in natural background soil sample were nearly 40 Bq/kg, Pa-234m not detected. According to the results of radiological characterization (field and laboratory), which showed an increase in radioactivity in the AL-Tahreer Tower Building the protective procedures had been adopted, where the contaminated soil and wastes resulted from decontamination processes collected in the 26 drum of capacity 220 liter, after the transfer of drums to the temporary storage at Tuwaitha site with cooperation of the Directorate of Radioactive Waste Management & Treatment at (MOST). Now the building within the background radiation levels and released by the regulatory body “Radiation Protection Center (RPC)/ Ministry of Environment (MOEN)”.

Evaluation of naturally occurring radioactive materials in oilfields of south east of Libya

An investigation was carried out to find out the concentration of NORMs in evaporation ponds sludge in south eastern oilfield of Libya. Activity concentrations of 226Ra, 232Th and 40K in soil generated during oil production operations were determined using a gamma spectroscopy system based on high purity germanium (HPGe) detector. Concentrations ranged from 83 to 1000 Bq kg−1 for 226Ra, 59 to 315 Bq kg−1 for 232Th and 109 to 304 Bq kg−1 for 40K. To evaluate the radiological effects, radium equivalent activity and external hazard are calculated. The magnitude of these results demonstrates the need of these ponds for a special treatment on site to reduce the exposure to a value below 100 μSv/y, by mixing the pond after drying the lagoon with clean soil to reduce the dose rate and minimise the environmental impact of NORM.

Assessment of Annual Effective Dose from Measured Soil Radioactivity Levels Using HPGe Detector

Human beings are persistently exposed to ionizing radiation caused by terrestrial, extra-terrestrial and anthropogenic radionuclides. In order to assess the risks associated with exposure due to the natural radioactivity in soil, a radiological environmental monitoring survey was carried out in district Chakwal. In the present study, activities of 226Ra, 232Th and 40K are measured in soil samples using an HPGe based gamma spectrometry system. The measured mean specific radioactivity concentration of 226Ra, 232Th and 40K in the studied samples was 31.08 ± 1.2 Bqkg-1, 47.67 ± 2.30 Bqkg-1 and 558.23 ± 17.52 Bqkg-1, respectively. From the measured activity concentration, radium equivalent activity, external and internal hazard indices, terrestrial absorbed dose and annual effective dose were calculated. Mean radium equivalent activity (Raeq), outdoor radiation hazard index (Hex), indoor radiation hazard index (Hin) and absorbed dose rate (D) for the area under study were determined as 142.18 Bqkg-1, 0.38, 0.47 and 66.13 nGyh-1 respectively. The annual effective dose equivalent (AEDE) varied in the range from 0.10 mSv y-1 to 0.16 mSv y-1. On the basis of measured activity and calculated values of hazards indices, it is concluded that the surveyed area does not pose any significant radiological risk to the population and environment.

Radiological maps for fallout 7Be in forest soil horizons in a mountainous area of Turkey

ABSTRACTDue to the paucity of data on separate spatial distribution of cosmogenic 7Be radionuclide activities in forest soil layers, a spatial study was performed in Mount Ida (Kazdagi)/Edremit, Turkey. In this study, it was aimed to examine the 7Be spatial variability and depth distribution in the surface soil layers. The 7Be activity concentrations were determined by HPGe gamma spectrometry system and the distributions of 7Be activities in the OL and OF + OH horizons throughout the region were mapped separately. Activity concentrations of 7Be in OL horizons and OF+OH horizons varied as 35 ± 23–701 ± 40 Bq kg−1 and 0.96 ± 0.63–197 ± 11 Bq kg−1, respectively. 7Be inventories (0.20 ± 0.06–5.69 ± 0.75 kBq m−2) in the study area were relatively higher when compared with the other regions of the world. 7Be inventories increased with altitude, slope and the thickness of the humus layer in some of the investigated area. Average 7Be activity level in deciduous forest stand type was significantly higher than that for coniferous and mixed stand types. Our limited data could not provide a latitudinal distribution pattern of 7Be soil inventory or precipitation dependence and further investigation is needed.

Assessment of radiation hazards due to exposure to radionuclides in marble and ceramic commonly used as decorative building materials in Egypt

The concentrations of 238 U (226Ra), 232Th, and 40K for the commonly used decorative building materials (15 marble and 15 ceramic) in Egypt were measured using gamma spectroscopy system. Radionuclides concentrations in marble samples were ranged from: ND to 49.92 ± 7.74 Bq kg−1 for 226Ra, 8.30 ± 1.70 to 119.52 ± 16.00 Bq kg−1 for 232Th, and 32.60 ± 4.25 to 2238.33 ± 242.66 Bq kg−1 for 40K while in ceramic samples the concentration ranged from: 28.42 ± 5.41 to 118.70 ± 20.34 Bq kg−1 for 226Ra, 30.65 ± 5.49 to 114.15 ± 18.78 Bq kg−1 for 232Th, and 389.54 ± 49.57 to 1069.83 ± 124.50 Bq kg−1 for 40K, respectively. These results imply that radium and thorium concentrations were below the worldwide recommended values but potassium was above the standard guideline. Radiological hazards indices of radium equivalent activity (Raeq), external and internal hazard indices: Hex and Hin, respectively, and annual effective doses of the investigated materials due to the presence of those radionuclides were calculated and had values less than the worldwide recommended values of 370 Bq kg−1, unity and 1 mSv y−1, respectively. Therefore, the studied types of marble and ceramic can be safely used as decorative building materials.

Evaluation of forest decontamination using radiometric measurements

An experiment has been conducted to evaluate the additional dose reduction by clear felling contaminated forestry in Fukushima Prefecture, Japan, and using the timber to cover the areas with wood chips. A portable gamma spectrometry system, comprising a backpack containing a 3 × 3″ NaI(Tl) detector with digital spectrometer and GPS receiver, has been used to map dose rate and radionuclide activity concentrations before, after and at stages during this experiment. The data show the effect of the different stages of the experiment on dose rate at different locations around the site. The spectrometric data have allowed the assessment of the contributions of natural and anthropogenic radionuclides to the dose rate at different parts of the site before and after the experiment. This has clearly demonstrated the value of radiometric methods in evaluating remediation, and the effect of other environmental processes. The value of spectrometric methods which directly measure radionuclide concentrations has also been shown, especially through the identification of the contribution of natural and anthropogenic activity to the measured dose rate. The experiment has shown that clearing trees and applying wood chips can reduce dose rates by 10–15% beyond that achieved by just clearing the forest litter and natural redistribution of radiocaesium.

Minimum Detectable Activity in gamma spectrometry and its use in low level activity measurements

In this paper there are described three different algorithms of Minimum Detectable Activity (MDA) calculus, and its use in high resolution gamma spectrometry. In the first part, few introductive theoretical aspects related to the MDA are presented. Further, the theory was applied to real gamma rays spectrometry measurements and the results were compared with the activities reference values. Two different gamma spectrometry systems, both of them using High Purity Germanium (HPGe) detectors, but having different efficiencies, were used. Samples having different geometries and radionuclides content were measured. The measured samples were made by dissolving of some acids containing anthropogenic radionuclides in water, obtaining a density of 1g/cm3. Choosing this type of matrix was done because of its high homogeneity.

Natural Radioactivity and Associated Dose Rates in Soil Samples in the Destroyed Fuel Fabrication Facility, Iraq

The activity concentrations of naturally occurring radionuclides 226Ra, 232Th and 40K in soil samples collected from Fuel Fabrication Facility in Al-Tuwaitha nuclear site were measured by using a high resolution gamma spectrometry system via High Purity Germanium (HPGe) Detector with a relative efficiency of (>40%) and resolution (<1.8keV) at energy of (1.33MeV) for 60Co. The average activity concentrations of 226Ra, 232Th and 40K in soil samples were found to be 15.78±1.16, 14.09±1.33 and 306.42±18.1 Bqkg-1, respectively. The results obtained for the corresponding radionuclides are lower than the worldwide average values of 35, 30, and 400 Bqkg-1, respectively. The average absorbed dose rate in air (Dγ), the average radium equivalent activity (Raeq) and the average external hazard index (Hex) were determined as 28.90±2.12 nGyh-1, 59.52±4.45 Bqkg-1 and 0.16±0.012, respectively, which are below the permissible limit.

NATURAL RADIOACTIVITY IN SEDIMENTS AND RIVER BANK SOIL OF KALLADA RIVER OF KERALA, SOUTH INDIA AND ASSOCIATED RADIOLOGICAL RISK.

The paper presents the activity concentrations of 232Th, 226Ra and 40K in the sediments and river bank soil samples collected from the Kallada river environs of coastal Kerala. The radiological risks associated with these radionuclides were calculated. The samples were processed following standard procedure, and activity was counted using a high-efficiency 5″ × 5″ NaI (Tl) detector coupled to GSPEC gamma spectroscopy system. The mean values of measured activities of 232Th, 226Ra and 40K in soil samples were found to be 98.1 ± 0.4, 60.3 ± 1.1 and 343.4 ± 1.8 Bq kg-1, respectively, which results in an average absorbed dose rate of 103 nGy h-1 The corresponding values for sediment samples were found to be 88.0 ± 0.4, 48.6 ± 0.9 and 423.2 ± 2.0 Bq kg-1, respectively, with a resulting absorbed dose rate of 95 nGy h-1 Radium equivalent activity, annual effective dose equivalent, the external and internal hazard indices were determined and compared with recommended limits. The results of the work provide background data on natural radioactive isotopes, which are useful in the assessment of human radiation exposure from natural environment. The accumulation of information on natural radiation is of great value for radiation protection.

Instrumental neutron activation analysis, gamma spectrometry and geographic information system techniques in the determination and mapping of rare earth element in phosphogypsum stacks

Phosphogypsum is a by-product from the phosphate fertilizer industry, disposed in huge stacks in open-air storage areas. Its use in agriculture may be a solution to decrease these stacks, because, among its other uses, phosphogypsum can be used as a soil amendment to provide calcium and sulphur for major crops. However, it contains rare earth elements (REE) from its raw material. The objective of this study was to determine the concentrations of REE in phosphogypsum stacks Imbituba (southern Brazil) in order to verify the possibility of contamination in the surrounding of the stacks due to the disposal and to ensure the safe use of phosphogypsum in agriculture. Samples of phosphogypsum were collected and REE were determined by neutron activation analysis and gamma spectrometry. There was no leaching of the REE through the profile of the stacks, which suggests that the occurrence of REE in the phosphogypsum is associated with the formation of sulphates, carbonates, fluorides and phosphates. The results indicate that application of phosphogypsum from Imbituba to agricultural soils can contribute to increase the concentration of rare earth elements in the cultivated soils, but these are not available to plant uptake.

Evaluation of a Modified HPGe Preamplifier for High-Rate Spectroscopy Measurements in a Pulsed Photonuclear Environment

Pulsed photonuclear techniques are commonly used in homeland security and nuclear safeguards applications to achieve enhanced detection sensitivity. For example, photoneutrons generated by a pulse-mode linear accelerator (linac) are commonly utilized to produce characteristic capture gamma rays for the detection of nitrogen-rich explosives. Recently, in an effort to develop innovative systems with increased sensitivity to detect diversion and prevent misuse, the authors proposed to assay used nuclear fuel for its plutonium content using a photofission technique, in support of nuclear material management in the U.S. fuel cycle.Passive spectroscopy measurements in the presence of intense background from fission products could be very difficult. Focusing on high-energy delayed gamma rays emitted by short-lived products from photofission presents a much more promising solution. However, as discovered in this study, a commercially available standard high-purity germanium (HPGe) preamplifier can be easily saturated for tens of milliseconds after each linac pulse. This greatly reduces the live time of the system especially when the linac repetition rate is high. On the other hand, although significantly reduced by increasing the lower-level threshold, the input count rate can still easily reach 106 cps (counts per second). Developing a gamma spectroscopy system that can handle such a high count rate has been a major challenge.In this work, a commercial HPGe preamplifier was modified to reduce the saturation time and tail time to improve its high-rate performance in a pulsed photonuclear environment. Results of the modifications were evaluated via both simulations and experiments and proven to be effective without significant degradation of energy resolution. The field-effect transistor (FET) and feedback components were first moved to the warm side to enable the modifications. The saturation time of the preamplifier following a linac pulse was greatly reduced by decreasing the value of the feedback resistor. The effect of reducing the tail time of the output signal was also studied. A traditional trapezoidal shaping approach was then employed to study the impact of the modifications on energy resolution.

Comparison of two spectrometric counting modes for fast analysis of selected radionuclides activity

The two counting modes: a normal with a single HPGE detector and second with the additional anti-Compton shield of the annular NaI(Tl) detector have been compared for fast determination of the activity concentration of thorium 232Th in the building materials. The 232Th activity concentration was calculated by measurement of its decay products: 212Pb, 212Bi and 208Tl as well 228Ac content. Although the Compton suppression mode applied in gamma spectrometry systems in general increase sensitivity of the analysis, but in case of 583 keV the most abundant 208Tl γ-line, the significant reduction of photon counting rate was observed.