Rana Baydoun

Determination of natural and artificial radioactivity in soil at North Lebanon province

The concentrations of natural and artificial radionuclides at 57 sampling locations along the North Province of Lebanon are reported. The samples were collected from uncultivated areas in a region not previously reported. The samples were analyzed by gamma spectrometers with High Purity Germanium detectors of 30% and 40% relative efficiency. The activity concentrations of primordial naturally occurring radionuclides of (238)U, (232)Th, and (40)K varied between 4-73 Bq kg(-1), 5-50 Bq kg(-1), and 57-554 Bq kg(-1) respectively. The surface activity concentrations due to the presence of these radionuclides were calculated and Kriging-geostatistical method was used to plot the obtained data on the Lebanese radioactive map. The results for (238)U, (232)Th, and (40)K ranged from 0.2 kBq m(-2) to 9 kBq m(-2), from 0.2 kBq m(-2) to 3 kBq m(-2), and from 3 kBq m(-2) to 29 kBq m(-2) respectively. For the anthropogenic radionuclides, the activity concentrations of (137)Cs founded in soil ranged from 2 Bq kg(-1) to 113 Bq kg(-1), and the surface activity concentration from 0.1 kBq m(-2) to 5 kBq m(-2). The total absorbed gamma dose rates in air from natural and artificial radionuclides in these locations were calculated. The minimum value was 6 nGy h(-1) and the highest one was 135 nGy h(-1) with an average of 55 nGy h(-1) in which the natural terrestrial radiation contributes in 99% and the artificial radionuclides mainly (137)Cs contributes only in 1%. The total effective dose calculated varied in the range of 7 μSv y(-1) and 166 μSv y(-1) while the average value was 69 μSv y(-1) which is below the permissible limit 1000 μSv y(-1).

Activity concentrations and mean annual effective dose from gamma-emitting radionuclides in the Lebanese diet

Since the primary factor contributing to the internal effective dose in the human organism is contaminated food, the control of radionuclides in food represents the most important means of protection. This study was conducted to determine the levels of the dietary exposure of the Lebanese population to gamma-emitting radioisotopes. The activity concentrations of gamma-emitting radioisotopes have been measured in food samples that represent the market basket of an adult urban population in Lebanon. The artificial radionuclide (137)Cs was measured above detection limits in only fish, meat and milk-based deserts. The most abundant natural radionuclide was 40K (31-121 Bq kg(-1)), with the highest content in fish and meat samples. The annual mean effective dose contributed by 40K in the reference typical diet was estimated equal to 186 microSv y(-1), a value reasonably consistent with findings reported by several other countries.

Set-up, optimization and first set of samples at the radiocarbon laboratory in Lebanon

A new radiocarbon laboratory has been established recently at the Lebanese Atomic Energy Commission. This laboratory consists of benzene synthesis line and a low background liquid scintillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard detector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintillation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three different counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student’s t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future research in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ14C) deduced from the Percent Modern Carbon or PMC. This work represents the results of four reference materials and those of five green grass samples. The Δ14C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.

Seasonal Variations of Radiocarbon Content in Plant Leaves in a 14 C-Depleted Area

The determination of radiocarbon content in biogenic samples such as tree leaves and short-lived plants is crucial when studying the anthropogenic impact on the ecosystem and for detecting any alteration in stable and radioactive CO 2 . A total of 76 samples of evergreen and deciduous tree leaves as well seasonal plants were collected in winter, spring, and summer. Sampling was carried out from rural villages located in Mount Lebanon Province, Lebanon. Based on the data obtained from a previous study carried out in autumn, which showed that the selected sites are characterized by depletion of 14 C caused by the releases of pollutants and CO 2 from a cement factory in the region, further investigation was carried out in the present work to determine possible significant seasonal variations in Δ 14 C values. Reference samples of identical species were collected in the same period from a clean zone. The conventional 14 C method was used to determine the carbon isotopic ratio. Δ 14 C data are compared to those obtained in autumn. 14 C concentration in the studied sites was significantly lower than in the clean area in all seasons. ANOVA tests showed that there is a significant seasonal variation for deciduous leaves and seasonal plants, while this difference was not significant in evergreen leaves. In addition, no significant variation was recognized for different species in the same season. DOI: 10.2458/azu_rc.57.18350

Method validation for the determination of fraction of modern (F14C) in wood samples using conventional method

Abstract The radiocarbon laboratory at the Lebanese Atomic Energy Commission is undertaking environmental studies, in order to determine the anthropogenic impact of technologies on the ecosystem through the determination of radiocarbon content in tree leaves and plants. Thus, it was important to validate the method used to demonstrate that the applied procedure gives reliable results. Method validation is universally applied in analytical laboratories as an essential part of quality assurance system and as a basic technical requirement of the ISO 17025 standard. The conventional method used for determination of Fraction Modern (F14C) is a standard method issued by the American Society for Testing and Materials in 2011 with a code ASTM-D 6866-11 Method C. According to Eurachem guide, internal validation was expressed in terms of accuracy that was evaluated by trueness and precision. Trueness was expressed in terms of relative bias, while for precision ten consecutive replicates were carried out to under repeatability conditions and five duplicates were analyzed under reproducibility conditions. The limit of detection and the minimum detectable activity (MDA) were calculated. Uncertainty sources were defined and their relative standard uncertainties were calculated in order to determine the combined standard uncertainty. Five reference samples of different matrices were analyzed; calculated z score values were acceptable as being between –2 and +2. The calculation and results are presented in this work.