Isodose Map Research Articles

Isodose mapping of terrestrial gamma radiation in Sarawak-Borneo: Insights from surface-weathered soil analysis

Presentation of baseline data on terrestrial gamma radiation (TGR) levels is crucial for assessing the annual effective dose received by the public due to natural radiation exposure. Cumulative doses from various sources can become significant, warranting a spatial understanding of TGR distribution. Few countries have comprehensively mapped TGR on a national scale, often facing challenges due to remote or inaccessible regions. This study investigated the influence of weathered soil groups on TGR dose rates in Sarawak-Borneo, Malaysia, to facilitate insights for TGR projection and isodose mapping. A total of 1044 TGR dose rate measurements were collected using NaI (Tl) scintillation detector survey meters, with a mean of 100 nGy h−1 and a range of 8–375 nGy h−1. Non-parametric statistical analyses of variance using Welch's ANOVA, Brown-Forsythe, and Kruskal-Wallis validated (P-sig.=.000) notable dissimilarities among six categories of superficial-weathered soil. Graphical analysis using Sinclair's cumulative plot revealed deviations at intervals of 50, 80, 100, 120, 175, and 205 nGy h−1. These deviations indicate distinct lithological influences. Skeletal soil (entisols) and podzolic soils had high mean dose rates (148 and 113 nGy h−1, respectively) due to limited development, thus preserving abundant uranium (U) and thorium (Th). Meanwhile, gleysols and thionic soils exhibited compatible means (90 and 82 nGy h−1, respectively), while alluvial (or transported soils) and organic soils displayed lower dose rate ranges (mean of 76 and 47 nGy h−1, respectively), reflecting rapid hydrolysis weathering processes. Simple linear regression analysis revealed a strong relationship between TGR dose rate and mean value of weathered soil groups (y = 0.851x + 0.141 nGy h−1), signifying the significance and magnitude of weathered soil groups' impact on TGR dose rates. The obtained R-value is 0.704, indicating a strong linear correlation among soil group variables, and a Durbin-Watson statistic of 1.41, suggesting positive autocorrelation among residuals, thus positive relationships. An isodose map was successfully developed using the Kriging technique, aligning with lithological features of the study area. Semivariogram analysis reveals spatial dependence within a range of 1.47°, supporting the Kriging technique's suitability for spatial inference. In conclusion, this study has successfully revealed the relationship between TGR dose rates and superficial-weathered soil in Sarawak-Borneo. While the linear relationship is applicable to the Sundaland-Borneo tectonic block, it has potential to be used as a valuable tool for spatial inference of TGR dose rates in isodose development with similar lithologial characteristics, aiding in radiation exposure assessment and environmental monitoring.

MEASUREMENTS OF SEASONAL VARIATIONS OF RADIOACTIVITY DISTRIBUTIONS IN RIVERINE SOIL SEDIMENT OF ADO-ODO OTA, SOUTH-WEST NIGERIA: PROBABILISTIC APPROACH USING MONTE CARLO.

The radioactivity levels were measured using a hand-held gamma-ray survey meter and NaI (Tl) based gamma spectroscopy to evaluate the seasonal variation of radioactivity levels in the riverine area of Ado-Odo Ota. The measured iso-dose map reported higher gamma dose rate of 79nGy/h, approximately 34% higher than the world average of 59nGy/h. The values for U-238, Th-232 and K-40 activity levels ranged between 29.9 and 21.6; 103.2 and 31.2; 802.2 and 233.5 with mean values of 26.1, 55.6 and 499.3Bq/kg, respectively. According to the mean, 5th and 95th percentiles of the probabilities using the Monte Carlo simulation, the Radium equivalent activities and the absorbed dose rates are within their respective recommended limits of 370Bq/kg and 84 nGy/h. This study could be used to monitor dose rates and radiological risks for the areas covering the small area (Ado-Odo Ota) to the larger area (West African Region) as baseline data.

Assessment of health risk associated with natural gamma dose rate levels and isodose mapping of Jordan

ABSTRACTAs a pioneering study in Jordan, an extensive measurement for external gamma dose rate (GDR) was conducted. A portable gamma radiation detector was used to perform these measurements at 1 m above the soil surface. A geographical positioning system Garmin was used to record a total of 823 measured points. The GDRs’ measurement ranged from 35 to 470 nGy h−1 giving a mean value of 90 nGy h−1, which was found to be one and half times higher than the world average of 59 nGy h−1. The lowest mean GDR 72 nGy h−1 was found in the Albalqa governate, while the highest mean GDR 131 nGy h−1 was found to be for the Alkarak governate. The mean annual effective dose was found to be 0.551 mSv, which is higher than the world average value of 0.48 mSv. This is a pivotal study evaluating the risks associated with GDR levels in Jordan that were the relative excess lifetime cancer risk, the mean collective effective dose, the mean weighted GDR and the mean lifetime dose that are 2.24 × 10−3, 5538manSv y−1, 0.531 mSv and 39 mSv, respectively. The cosmic rays mean GDR was determined to be 20 nGy h−1. This study focuses on constructing GDRs’ baseline data in Jordan, which will be used to determine the possible change in the natural radiation due to other human activities in the future. ArcGIS software was employed to generate an isodose map to characterise exposure rates caused by GDR in Jordan.

Geological influence on the terrestrial gamma radiation dose rate in Jos Plateau, Nigeria

Natural environmental terrestrial gamma radiation dose (TGRD) rate measurements have been carried out across the geological formations of Jos Plateau, Nigeria. External gamma radiation dose rates ranged between 11 and 714 nGy h-1 with a mean value of 204 nGy h-1. Relationship between TGRD levels and geological type was determined. Statistical comparative method one way analysis of variance (ANOVA) was used to compare the TGRD means for the various types. The statistical results revealed in some instances, significant differences among the mean values of TGRD rates for the different underlying geological structures. Annual effective dose and collective effective dose for the general public due to exposure to terrestrial gamma radiation were estimated at 0.25 mSv y-1 and 1.20x102 mSv y-1, respectively. Isodose map for exposure rate due to TGRD wasplotted using ArcGIS software. The results will serve as database for natural background radiation for the country.Keywords: Natural radiation; Terrestrial gamma radiation dose (TGRD); geological type; Analysis of variance (ANOVA)

Assessment of natural background radiation in one of the highest regions of Ecuador

Natural background radiation was measured in the province of Chimborazo (Ecuador) with the following reference coordinates 1°40'00''S 78°39'00''W, where the furthest point to the center of the planet is located. Natural background radiation measurements were performed at 130 randomly selected sites using a Geiger Müller GCA-07W portable detector; these measurements were run at 6m away from buildings or walls and 1m above the ground. The global average natural background radiation established by UNSCEAR is 2.4mSvy−1. In the study area measurements ranged from 0.57mSvy−1 to 3.09mSvy−1 with a mean value of 1.57mSvy−1, the maximum value was recorded in the north of the study area at 5073metres above sea level (m.a.s.l.), and the minimum value was recorded in the southwestern area at 297m.a.s.l. An isodose map was plotted to represent the equivalent dose rate due to natural background radiation. An analysis of variance (ANOVA) between the data of the high and low regions of the study area showed a significant difference (p < α), in addition a linear correlation coefficient of 0.92 was obtained, supporting the hypothesis that in high altitude zones extraterrestrial radiation contributes significantly to natural background radiation.

Estimation of Terrestrial gamma radiation (TGR) dose rate in characteristic geological formations of Jos Plateau, Nigeria

A study was conducted to estimate the terrestrial gamma radiation (TGR) dose rates associated with the natural radionuclides 238U, 232Th and 40K in the characteristic geological formations of Jos Plateau. A total of 51 surface soils from all the geological units were collected and measured using high-resolution gamma ray spectrometry system. From the measured activity concentrations of 238U, 232Th and 40K, TGR dose rates in air outdoors 1 m above ground surface, were estimated to be in the range of 36 nGy h-1 to 456 nGy h-1, depending on the geological formation, with an overall mean value of 143 nGy h-1. The estimated mean value is by a factor of two higher than the world average value of 59 nGy h-1. Geological formation G8 (Younger granites) appear to have the highest mean TGR dose rate while G7 (sandstone, clay and shale) show the lowest mean TGR dose rate. The results of this study inferred that, TGR dose rates outdoors for Jos Plateau differs with the different geological formations and significantly contributed by 232Th. An isodose map for the distribution of TGR and exposure rate to the public due to natural sources was also plotted using ArcGIS software. The data here presented can be used to evaluate public radiation dose and to produce radiological map for the country.

Comparison of computed tomography shielding design methods using RadShield

Purpose. To comprehensively compare four computed tomography (CT) scanner shielding design methods using RadShield, a Java-based graphical user interface (GUI). Methods. RadShield, a floor plan based GUI, was extended to calculate air kerma and barrier thickness using accepted methods from the National Council on Radiation Protection and Measurements (NCRP), the British Institute of Radiology, and a method using isodose maps, for spatially distributed points beyond user defined barriers. For a stationary CT scanner, the overall shielding recommendations found using RadShield were also compared to those found by American Board of Radiology certified diagnostic medical physicists using the conventional NCRP dose length product method and the isodose map method. Results. The results between methods differed significantly for calculation point locations beyond the gantry and to the rear of the gantry. Overall shielding design recommendations across the four methods yielded similar average air kerma and thickness values for the barriers. Conclusions. RadShield was extended to perform CT shielding design and proved reliable using four methods.

Mapping of natural gamma radiation (NGR) dose rate distribution in tin mining areas of Jos Plateau, Nigeria

An extensive study was conducted to measure the natural gamma radiation (NGR) dose rates for the tin mining areas of Jos Plateau with an objective to establish a reference data record on the levels and distribution of natural background gamma radiation. The measurement was carried out using a portable NaI(Tl) scintillation survey meter. The results obtained, varied significantly for different soil types and for geological features of the study area. NGR dose rates values ranged between 40 nGy h−1 measured on Ferric Luvisols–Ferric Luvisols (S13) soil type, underlain by geological formation G7 (sandstone, clay and shale) and 1265 nGy h−1 recorded on, Haplic Acrisols (S27), underlain by geological formation G8 (Younger granites) with overall mean value of 250 nGy h−1. This is by a factor of four higher than the reported world average value of 59 nGy h−1. Mean indoor and outdoor annual effective dose for the public was estimated to be 1.2 and 0.31 mSv/y, respectively. An isodose map for the distribution and exposure rate due to natural sources radiation for the study area was also plotted using ArcGis software. The data here presented can use to prepare a national radiological map for the country.

Terrestrial gamma radiation dose (TGRD) levels in northern zone of Jos Plateau, Nigeria: Statistical relationship between dose rates and geological formations

In- situ measurement of terrestrial gamma radiation dose rates (TGRD) was conducted in northern zone of Jos Plateau and a statistical relationship between the TGRD and the underlying geological formations was investigated. The TGRD rates in all the measurements ranged from 40 to 1265nGyh−1 with a mean value of 250nGy h−1. The maximum TGDR was recorded on geological type G8 (Younger Granites) at Bisitchi, and the lowest TGDR was recorded on G6 (Basaltic rocks) at Gabia. One way analysis of variance (ANOVA) statistical test was used to compared the data. Significantly, the results of this study inferred a strong relationship between TGRD levels with geological structures of a place. An isodose map was plotted to represent exposure rates due to TGRD. The results of this investigation could be useful for multiple public interest such as evaluating public dose for the area.

Terrestrial gamma radiation dose rate in Cienfuegos, Cuba

This study assesses the level of background radiation for Cienfuegos Province, Cuba. Measurements of outdoor gamma radiation (of terrestrial and cosmic origin) in air were performed at 198 locations using a GPS navigator and a dose meter (SRP-68-01, 30 × 25 mm NaI detector). The average absorbed dose was found to be 73.9 nGy h -1 (17.2–293.9 nGy h -1 ), corresponding to an annual effective dose of 74.7 μ Sv (21–324 μ Sv). When compared with the data available for other places, the absorbed gamma doses obtained in this study indicate a background radiation level that falls within natural limits for the Damuji, Salado and Caonao watersheds; however, the Arimao and Gavilanes watersheds present levels of the absorbed dose and annual effective dose comparable with high background radiation areas. An isodose map of the terrestrial gamma dose rate in Cienfuegos was drawn using the GIS application “Arc View”. This study provides important baseline data of radiation exposure in the area.

Predicting terrestrial gamma dose rate based on geological and soil information: case study of Perak state, Malaysia

An extensive terrestrial gamma radiation dose (TGRD) rate survey has been conducted in Perak State, Peninsular Malaysia. The survey has been carried out taking into account geological and soil information, involving 2930 in situ surveys. Based on geological and soil information collected during TGRD rate measurements, TGRD rates have been predicted in Perak State using a statistical regression analysis which would be helpful to focus surveys in areas that are difficult to access. An equation was formulated according to a linear relationship between TGRD rates, geological contexts and soil types. The comparison of in situ measurements and predicted TGRD dose rates was tabulated and showed good agreement with the linear regression equation. The TGRD rates in the study area ranged from 38 nGy h−1 to 1039 nGy h−1 with a mean value of 224 ± 138 nGy h−1. This value is higher than the world average as reported in UNSCEAR . The TGRD rates contribute an average dose rate of 1.37 mSv per year. An isodose map for the study area was developed using a Kriging method based on predicted and in situ TGRD rate values.

Radiological mapping of Kelantan, Malaysia, using terrestrial radiation dose rate

Measurements of the environmental terrestrial gamma radiation dose rate (TGRD) in each district of Kelantan state, Malaysia, were carried out using a portable hand-held radiation survey meter and global positioning system. The measurements were done based on geology and soil types of the area. The mean TGRD was found to be 209 nGy h–1. Few areas of relatively enhanced activity were observed in Pasir Mas, Tanah Merah and Jeli districts, which have a mean TGRD between 300 and 500 nGy h–1. An isodose map of the area was produced using ArcGIS software version 9.3.

Terrestrial gamma radiation dose rates and radiological mapping of Terengganu state, Malaysia

Measurement of terrestrial gamma radiation dose (TGRD) rates in Terengganu state, Malaysia was carried out from 145 different locations using NaI[Tl] micro roentgen survey meter. The measured TGRD rates ranged from 35 to 340 nGy h−1 with mean value of 150 nGy h−1. The annual effective dose to population was found to be 0.92 mSv y−1. The data obtained were used in constructing the gamma isodose map using ArcGis 9.3 which shows the distribution of TGRD rates across the state.

Measurement of terrestrial gamma radiation dose-rate (TGRD) level in soil samples from the district of Rembau, Malaysia, using high-purity Germanium detectors

This study assesses the gamma radiation levels and associated dose rates from the naturally occurring radionuclides 232Th, 238U and 40K in soil samples collected from the district of Rembau, Malaysia using High-purity Germanium (HPGe) Detectors. A 105 measurement were performed on surface soil using NaI (Tl) gamma-ray detector with crystal size 1"x1", covering about 83% land of the Rembau district. The concentration of the naturally occurring radionuclides 232Th, 238U and 40K in soil samples collected were determined by using HPGe detector based on high-resolution gamma spectrometry system at Malaysia Nuclear Agency. The range of natural gamma radiation measured was from 114±14 nGy h−1 to 857±14 nGy h−1. The range of activity concentrations of U, Th and °K in soil from the studied areas varies from 151-401 Bq kg−1, 113-342 Bq kg−1 and 674-1526 Bq kg−1 with mean values of 245 Bq kg−1, 186 Bq kg−1 and 1152 Bq kg1 respectively. The mean values of terrestrial gamma radiation dose rate measured in Rembau district is 383±18 nGy h−1 compared to the Malaysian average is 92 nGy h−1 and world average is 59 nGy h−1 (UNSCEAR, 2000). The average annual dose from such terrestrial gamma radiation dose rates to an individual in Rembau district, assuming a tropical rural setting is estimated to be 0.78 mSv per year, which is considered to be within the normal range for doses from natural sources. An isodose map for the Rembau district has been plotted.

Isodose mapping of terrestrial gamma radiation dose rate of Selangor state, Kuala Lumpur and Putrajaya, Malaysia

A terrestrial gamma radiation survey for the state of Selangor, Kuala Lumpur and Putrajaya was conducted to obtain baseline data for environmental radiological health practices. Based on soil type, geological background and information from airborne survey maps, 95 survey points statistically representing the study area were determined. The measured doses varied according to geological background and soil types. They ranged from 17 nGy h−1 to 500 nGy h−1. The mean terrestrial gamma dose rate in air above the ground was 182 ± 81 nGy h−1. This is two times higher than the average dose rate of terrestrial gamma radiation in Malaysia which is 92 nGy h−1 (UNSCEAR 2000). An isodose map was produced to represent exposure rate from natural sources of terrestrial gamma radiation.

Spatial distribution and lifetime cancer risk due to gamma radioactivity in Yelagiri Hills, Tamilnadu, India

The spatial distribution of natural radioactivity due to uranium, thorium and potassium was investigated in soils from the undisturbed areas in Yelagiri Hills, Tamilnadu, India by Isodose map. The radiological hazards due to natural radionuclides content such as representative level index (RLI), activity utilization index (AUI), excess lifetime cancer risk (ELCR) and internal radiation hazards (Hin) of the soil samples in this area were calculated. The calculated radiological hazard parameters are compared with different countries of the world. The calculated range of ELCR is 0.326 × 10−3 to 1.067 × 10−3 with an average of 0.700 × 10−3 for soils. This average value of ELCR is more twice than the world average (0.290 × 10−3). A correlation analysis was made between measured dose rate and individual radionuclides, in order to delineate the contribution of the respective nuclides toward the dose rate. The U/Th concentration ratio in surface soil samples ranged from 0.05 to 1.72 with an average of 0.43 which is more higher (80%) than the world average of 0.26. The application of cluster analysis (CA) and principal component analysis (PCA), coupled with Pearson correlation coefficient analysis, were utilized to analyze the data, identify and clarify between the radiological parameters to know the existing relations. The CA and PCA results showed that the former method yielded three distinctive groups of the soil variables whereas the latter one yielded the number of variables into two factors with 94.47% variance explanation.

Terrestrial gamma dose rate in Pahang state Malaysia

Environmental terrestrial gamma radiations (TGR) were measured in Pahang state Malaysia between January and April 2013. The TGR dose rates ranged from 26 to 750 nGy h−1. The measurements were done based on geology and soil types of the area. The mean TGR dose rate was found to be 176 ± 5 nGy h−1. Few areas of relatively enhanced activity were located in Raub, Temerloh, Bentong and Rompin districts. These areas have external gamma dose rates of between 500 and 750 nGy h−1. An Isodose map of the state was produced using ArcGIS9 software version 9.3. To evaluate the radiological hazard due to terrestrial gamma dose, the annual effective dose equivalent and the mean population weighted dose rate were calculated and found to be 0.22 mSv year−1 and 168 nGy h−1 respectively.

Absorbed dose to lesion and clinical outcome after liver radioembolization with 90Y microspheres: a case report of PET-based dosimetry

A 54-year-old woman with metastatic colorectal carcinoma underwent liver radioembolization with (90)Y resin microspheres. Microsphere biodistribution was assessed 2h after the treatment through a 20-min long (90)Y PET scan. Isodose map and lesion dose-volume histogram (DVH) were then evaluated using a MATLAB-based code. Response to therapy was assessed performing a (18)F-FDG PET 6months after the treatment. At (90)Y PET the patient showed a well-defined horseshoe-shaped hepatic lesion with hot margins and a cold core. The lesion presented a heterogeneous DVH with a hot margin receiving an average radiation dose as high as 287Gy and a cold area receiving an average radiation dose of 70Gy approximately. Six months after the treatment the patient reported a complete remission of tumour areas which received a high radiation dose, while progression of metastases was observed in the area that presented scarce microsphere localization at (90)Y PET. According to our experience, the use of (90)Y PET voxel dosimetry may provide a useful tool to assess possible correlations between microsphere biodistribution and clinical outcome of the treatment. In agreement with current literature findings, an average radiation dose greater than approximately 100Gy may be required to sterilize liver metastases.

Terrestrial gamma radiation and its statistical relation with geological formation in the Mersing district, Johor, Malaysia

An extensive survey was carried out for gamma dose rates (GDRs) in the Mersing district, Johor, Malaysia. The average value of GDR measured in the district was found to be 140 nGy h(-1), in the range of 40-355 nGy h(-1). The mean weighted dose rate to the population, annual effective dose equivalent, collective effective dose equivalent, lifetime cancer risk were 0.836 mSv y(-1), 0.171 mSv, 1.18 × 10(1) man Sv y(-1) and 6.98 × 10(-4) Sv y, respectively. An isodose map was produced for the district. One way analysis of variance was used to test for differences due to different geological formations present in the Mersing District.

Radiological monitoring: terrestrial natural radionuclides in Kinta District, Perak, Malaysia

Natural background gamma radiation and radioactivity concentrations were investigated from 2003 to 2005 in Kinta District, Perak, Malaysia. Sample locations were distant from any ‘amang’ processing plants. The external gamma dose rates ranged from 39 to 1039 nGy h −1. The mean external gamma dose rate was 222 ± 191 nGy h −1. Small areas of relatively enhanced activity were located having external gamma dose rates of up to 1039 ± 104 nGy h −1. The activity concentrations of 238U, 232Th and 40K were analyzed by using a high-resolution co-axial HPGe detector system. The activity concentration ranges were 12–426 Bq kg −1 for 238U, 19–1377 Bq kg −1 for 232Th and <19–2204 Bq kg −1 for 40 K. Based on the radioactivity levels determined, the gamma-absorbed dose rates in air at 1 m above the ground were calculated. The calculated dose rates and measured dose rates had a good correlation coefficient, R of 0.94. To evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the gamma-absorbed dose rate and the mean population weighted dose rate were calculated. An isodose map for the Kinta District was also produced.