Radioisotopes In Environment Research Articles

Using 7Be and 137Cs for Assessing the Land Stability of Alexandria Region, Egypt

This paper presents an assessment of land stability using fallout environmental radioisotopes 7Be and 137Cs. The measurement of both isotopes was carried out in samples of soil collected from twenty-five sites covering the studied region. At each site, the samples were taken from five consecutive vertical depth levels to show the vertical displacement or compactness of the soil column. The collected samples were carefully transferred for radioactivity measurement at Alexandria University’s Institute of Graduate Studies and Research. A high-resolution gamma-ray spectrometer utilizing high-purity germanium was employed for the measurements. Surface distribution of the radionuclides levels was used to show the studied lands’ stability over the short- and long-term based on the used radionuclides’ nuclear half-life. For short-term (months) stability, 7Be (half-life: 35.5 days) levels showed that about 73% of the area is very low in stability, while the areas that recorded low, moderate, and high stability are at 18%, 4%, and 5%, respectively. For long-term (years) stability, 137Cs (half-life: 30 years) levels showed that about 80% of the areas are very low in stability, while the remaining areas, predicted as 12.8%, 5.6%, and 1.6%, are low, moderate, and high stability, respectively. It is clear that the eastern side of Alexandria is suffering from soil erosion and subsidence; on the other hand, the western side is more stable. Consequently, due to the origin of the soil, the nature of soil geological formations, and the environmental prevailing conditions, Alexandria is found to be more vulnerable to the consequences of sea-level rise and climate change. Therefore, adequate strategic management, including mitigation measures and adaptation, should be planned and implemented.

Hydrochemical and age constraints of the Chapada dos Veadeiros geothermal reservoir, central Brazil

This paper reports the first conceptual model of non-magmatic system in central Brazil, constrained by structural, hydrochemical and isotopic data. The study involved analyses of carbon, oxygen and hydrogen isotopes (14C,18O, 2H and ³H) in addition to the chemical signatures of water samples from natural springs and borehole. Samples were classified into three hydrochemical groups, based on their pH, electric conductivity (EC) and temperature. Group 1 shows the lowest temperature range and lowest pH and EC values (respectively averages of 27 °C, 5.0, and 15 μS/cm); Group 3 shows higher temperature, pH, EC (42 °C, 7.1, and 215 μS/cm); and Group 2 shows intermediate values (average of 38 °C, 6.2 and 80 μS/cm). The conceptual flow model indicates that the recharge area is located in the higher plateau areas and the only recharge source is rainwater. The groundwater flows towards the southwest for 15–25 km up to the São Joaquim fault system, where the hydraulic conductivity contrast, due to different rock types, induces upward flow to the hot springs area. Buoyancy due to heating through deep circulation can also influence the upward flow, however, it is not the main process. The flow path from NE to SW is controlled by secondary brittle structures, related to fractures represented by long lineaments. Environmental radioisotopes of water (3H and 14C) were used to determine the residence time of thermal waters. ³H data indicate that samples MV2 and TOC1 (respectively from groups 2 and 3), are related entirely to the deep thermal reservoir, with no mixing influence between reservoirs. Samples SJ1 and CH3 show ³H values from 0.9 to 0.64 TU, indicating mixture of water from recent cold waters and the deep thermal reservoir. Group 3 samples yielded a raw 14C age of 9270 years, and the most coherent correction model applied was the International Atomic Energy Agency, resulting in an age of 7877 years. Group 2 yielded age of 2280 years and the most consistent correction model applied was the Pearson equation, ensuing an age of 2281 years. Group 1 samples resulted in negative age, interpreted as contamination from external carbon sources likely related to algae. Sample SJ1 (from a deep well) yielded an age of 1,470, and the correction by the Pearson model resulted in age of 1352 years. The δ2H and δ18O data are plotted above the local meteoric water line, indicating enrichment of lighter isotopes. The values measured for the total dissolved solids; electric conductivity and pH are in agreement with the isotopic data interpretations, and with the aquifer mineralogy.

PLANTS COVERING INFLUENCE TO THE RADIOISOTOPES EXISTENCE OF Cs-137 AND Pb-210 IN THE SOIL

PLANTS COVERING INFLUENCE TO THE RADIOISOTOPES EXISTENCE OF 137Cs and 210Pbex IN THE SOIL. Cs-137 and Pbex-210 of environmental radioisotope content in the soil can be useful to estimate the rate of erosion/deposition in an area, by comparing the inventory value of Cs-137 or Pbex-210 in observed site with those in a stable reference site. Cs-137 and Pbex-210 stick very strongly at the surface of the soil (clay), so it can use as a tracer for the movement of soil. Plants very influence the existence of Cs-137 and Pbex-210 environmental radioisotopes as a cover. If without a plant cover, then this environmental radioisotope at the soil would be gone by rain off. This experiment aims to observe the effect of plant cover on the existence of Cs-137 and Pbex-210 at the soil in uncultivated land. Sampling had been done in two uncultivated lands when the land still covering by plants (2016) and after becoming vacant land (2018), using coring (10 cm) for the surface layer and coring (7 cm) for the depth of 20 cm. The result showed that the activity of 137Cs and 210Pbex environmental radioisotopes at the surface layer decreased very significantly, and total inventory values until the depth of 20 cm decreased quite significantly at a vacant land condition. The corrosion rate for the vacant land is higher than the planted land. The value of erosion rate using the 137Cs method is 44.1 t/ha.y (CBG); -4.3t/ha.y (BMC) and 4 t/ha.y (CBG); -27.1 t/ha.y (BMC) for planted land and vacant land, respectively. Meanwhile, using the 210 Pb ex method is -8 t/ha.y (CBG); -36.9 t/ha.y (BMC) for planted land and -58 t/ha.yrs (CBG), -79.9 t/ha.yrs (BMC) for vacant land.

Dating of hot springs at Attri, Tarabalo and Athmalik sites in Odisha, India using radiocarbon technique

In this study environmental radioisotopes of water (3H and 14C) were used to determine the residence time of thermal waters. The temperature of geothermal waters was found to be uniform (57.6 °C ± 0.75 °C) with similar field alkalinity and pH values. The δ13C values of thermal water ranged between − 21.3 and − 18.75‰, which clearly reflect no/minimum contribution of carbonate minerals to the system. Environmental tritium concentration was found to be very low in these thermal waters indicating insignificant recharge from modern sources. The Pearson modelled 14C ages were found to vary from 4964 to 17,714 years.

A Trial to Natural Neutron Radiography

Neutron radiography system without the use of artificial neutron source has been developed. It uses only natural neutrons which exist continuously in any place. The system consists of a high sensitivity neutron imaging device and neutron moderator. The imaging device used was a 2-dimensional photon counter system which has been developing so far for high sensitivity neutron imaging. However, further improvement of neutron sensitivity and reduction ofγ-ray response is no doubt indispensable, whileγ-rays originated by cosmic rays and environmental radio isotopes also exist with the flux in several orders of magnitude large compared with that of the neutrons.The environmental neutrons are originated by cosmic ray. The intensity of natural neutrons is changed with the environmental conditions. Interestingly, the neutrons were observed to increase considerably with the condition near the massive iron blocks. The phenomenon is useful for our purpose, while the main object of the natural neutron imaging system is the field inspection of large iron structures.

Estimation of groundwater residence time using environmental radioisotopes (14C,T) in carbonate aquifers, southern Poland

Triassic carbonate aquifers in the Upper Silesia region, affected by intense withdrawal, have been investigated by means of isotopic analyses of 14C, δ13C, δ2H, δ18O and 3H. The isotopic examinations were carried out in the 1970s and in the early 1980s, and it was the first application of tracers to estimate age and vulnerability for the contamination of groundwater in this region. Similar isotopic analyses were conducted in 2007 and 2008 with the same Triassic carbonate formation. The isotopic examinations were performed within the confined part of the carbonate formation, wherein aquifers are covered by semi-permeable deposits. The direct recharge of the aquifer occurs in the outcrop areas, but it mainly takes place due to percolation of the water through aquitards and erosional windows. The Triassic aquifer has been intensively drained by wells and by lead–zinc mines. Nowadays, the declining water demand and closure of some mines have induced a significant increase in the water table level. The detailed analysis of the results, including the radiocarbon age corrections and the comparison of radioisotope activities, has made it possible to estimate the range of residence time within the carbonate Triassic aquifer. This range from several tens to several tens of thousands indicates that the recharge of aquifers might have occurred between modern times and the Pleistocene. The apparent age of the water estimated on the basis of 14C activity was corrected considering the carbon isotope exchange and the diffusion between mobile water in fractures and stagnant water in micropores. The obtained corrected period of recharge corresponds to the result of investigations of noble gases, which were carried out in the 1990s. In almost half of the cases, groundwater is a mixture of young and old water. The mixing processes occur mainly in areas of heavy exploitation of the aquifer.

THE INFLUENCE OF CONVERSION MODEL CHOICE FOR EROSION RATE ESTIMATION AND THE SENSITIVITY OF THE RESULTS TO CHANGES IN THE MODEL PARAMETER

A study of soil erosion rates had been done on a slightly and long slope of cultivated area in Ciawi - Bogor, using 137Cs technique. The objective of the present study was to evaluate the applicability of the 137Cs technique in obtaining spatially distributed information of soil redistribution at small catchment. This paper reports the result of the choice of conversion model for erosion rate estimates and the sensitive of the changes in the model parameter. For this purpose, small site was selected, namely landuse I (LU-I). The top of a slope was chosen as a reference site. The erosion/deposit rate of individual sampling points was estimated using the conversion models, namely Proportional Model (PM), Mass Balance Model 1 (MBM1) and Mass Balance Model 2 (MBM2). A comparison of the conversion models showed that the lowest value is obtained by the PM. The MBM1 gave values closer to MBM2, but MBM2 gave a reliable values. In this study, a sensitivity analysis suggest that the conversion models are sensitive to changes in parameters that depend on the site conditions, but insensitive to changes in parameters that interact to the onset of 137Cs fallout input. Keywords: soil erosion, environmental radioisotope, cesium

Estimation of Soil Erosion Using Field and Modelling Approaches in an Undisturbed Arnhem Land Catchment, Northern Territory, Australia

AbstractAn assessment of slope erosion at Tin Camp Creek catchment, Arnhem Land, Northern Territory, Australia, was carried out using the fallout environmental radioisotope caesium‐137 (137Cs) as an indicator of soil erosion status, two numerical models (SIBERIA and the Revised Universal Soil Loss Equation (RUSLE)) and erosion pins. This undisturbed drainage basin is situated in the seasonally wet‐dry tropics, with high energy storms and a mean annual rainfall of 1389 mm. Tin Camp Creek catchment is unaffected by European agriculture or pastoral activities, but often experiences fire during the dry season. Two transects were sampled for 137Cs in 2002 and 2004, and two models were used to convert 137Cs measurements into soil loss estimates. Two methods using the theoretical Profile Distribution Model (PDM) gave net soil redistribution rates between +2.72 and –22.19 t ha−1 yr−1 and +2.95 and –24.06 t ha−1 yr−1, respectively, while an Australian empirical model (AEM) for uncultivated soils produced estimates between +1.84 and –7.00 t ha−1 yr−1 (negative values indicate soil erosion, positive, deposition). The RUSLE gave estimated soil losses for the two transects of approximately 10 t ha−1 yr−1, while the SIBERIA model produced values between 0.5 and 2 t ha−1 yr−1 for the transects and between 3.5 and 11 t ha−1 yr−1 for the total catchment. Average net soil losses of 14 and 15 t ha−1 yr−1 for the total catchment and slopes, respectively, were measured by erosion pins. The soil losses in the catchment are similar to those for some other transects in the Northern Territory and the Kimberley region of Western Australia (measured by the 137Cs AEM), even though these areas are affected by pastoral activities. This may be at least partly explained by erosion in Tin Camp Creek catchment during high intensity rainstorms at the commencement of the wet season, especially if the slopes have been affected by fire during the previous dry season.

Advances in Instrumentation and Methods for Environmental Radioisotope Monitoring

Radiation monitoring apparatus and methods are classified by main operation characteristics - minimal detectable activity (MDA) and the capability to separately identify nuclides from a mixture of several radionuclides. The lowest MDA per unit volume is achieved by a large-size device (large sample and scintillation crystal) using high-energy γ-photons for the identification of nuclides; MDA strongly depends on the size and effective atomic number of the crystal. If the examined sample contains a number, K, of nuclides, their separate identification without limitation of K can be carried out by the fitting method (the amplitude spectrum of measured signals is expanded over the spectra of separate nuclides). In cases where MDA per unit volume is less important, nuclides can be identified by γ-particles and low-energy β-photons with the use of a compact device - phoswich detector with two scintillation layers strongly differing in thickness and decay time.

Differentiation of palaeomarine and modern seawater intruded salinities in coastal groundwaters (of Karaikal and Tanjavur, India) based on inorganic chemistry, organic biomarker fingerprints and radiocarbon dating

Hydrosalinity evolution is examined in the Karaikal and Tanjavur coastal aquifers situated about 300 km south of Madras, Tamil Nadu, India. Ancient and modern sources of solutes in groundwaters have been differentiated using hydro-geochemical data, environmental radioisotope dates and organic biomarkers. Results from different techniques show consistently that the Pliocene aquifer possesses characteristic palmitoleic and oleic acid biomarkers, apparent 14C ages of more than 20 000 years and high I/Cl ratio; the modern marine-estuarine intruded groundwaters in the alluvial aquifer display relatively younger apparent 14C ages (modern to 3000 years), enriched potassium ion, low I/Cl ratio and contain vaccenic and hopanoic acid biomarkers, and they also tend to display transient changes in chemical characteristics. These results have practical importance with regard to identifying and controlling seawater intrusion in coastal areas.

Basal flow rate of Changme-Khangpu glacier, Sikkim Himalaya based on32Si and210Pb chronology

Using environmental radioisotopes silicon-32 and lead-210, the radiometric ages of ice at the surface and at 5 m depth at the snout of the Changme-Khangpu (ck) glacier have been calculated to be 100 and >650 years respectively. Based on i) these age estimates, ii) a net uniform accumulation rate of 0·7 m/yr of ice in the accumulation zone; and iii) applying a simple ice flow model assuming melting of ice of 1 cm/yr at the base of the glacier, it is demonstrated that the average basal flow rate of theck glacier is much smaller (at least by a factor of three) than that of 40 m/yr estimated for the surface ice. This observation is in good agreement with the earlier work on basal flow rates and indicates that the deeper ice near the bed rock travels much slower than the surface ice.