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

Abstract

Abstract: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 (Δ 14 C) 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 Δ 14 C 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‰.

Measurement of 14C Content in Leaves near a Cement Factory in Mount Lebanon

“…The obtained lithium carbide was then decomposed by vacuum hydrolysis, yielding acetylene (C 2 H 2 ), which was converted to benzene (C 6 H 6 ) using a vanadium catalyst regenerated previously at 300-400°C. Purification of benzene was carried out using sulfuric acid followed by vacuum sublimation (Baydoun et al 2014). Butyl-PBD was used as the scintillator in the proportion of 10 mg per 1 g of benzene.…”

“…Normalization was carried out routinely to check stability of the counting system. The counting region optimization was conducted to maximize the factor of merit (FOM = E 2 /B), which was calculated at three counting windows (Baydoun et al 2014), where E is the efficiency and B is the background count rate (Bronić et al 2009;Knoll 2010). For this purpose, a blank sample containing commercial dead benzene purchased from Sigma-Aldrich, and a standard sample, oxalic acid II from NIST-SRM 4990C, were prepared and measured in the adopted counting geometry with 20-mL glass vials (Baydoun et al 2014).…”

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

“…Reference values are presented in Table 5. All reference samples were dried at 105°C without any previous chemical treatment (Różański et al, 1992;Baydoun et al, 2014).…”

“…The data presented are obtained from weekly measurements made on the same weekday over the period of six months. The counting region optimization was performed to maximize the figure of merit (FOM = E 2 /B) which was calculated at three counting windows where E is the efficiency and B is the background count rate of the blank (Bronić et al, 2009;Baydoun et al, 2014). For this purpose, blank sample containing 4 g commercial dead benzene and a standard sample were measured in the adopted counting geometry (4 g benzene).…”

“…Optimization was carried out to test the effectiveness of the lab through the analysis of a set of reference materials and left over proficiency test samples. As well as calibration, normalization of the measurement system was applied, counting regions were set for both Teflon and glass vials and stability of standards used was tested (Baydoun et al, 2014).…”