Naslov
A critical review of atmospheric 14C activities

Autori
Krajcar Bronić, Ines ; Horvatinčić, Nada ; Barešić, Jadranka ; Obelić, Bogomil ; Vreča, Polona

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Radiation Protection: From Knowledge to Action, Book of Abstracts, Second European IRPA Congress on Radiation Protection / IRPA - Pariz : SFRP, 2006

Skup
Second European IRPA Congress on Radiation Protection, Radiation Protection: From Knowledge to Action

Mjesto i datum
Pariz, Francuska, 15.05.2006. - 19.05.2006

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
14C; atmopshere; CO2; clean-air sites

Sažetak
14C activity of atmospheric CO2 has been measured at the Rudjer Bošković Institute as a part of environmental monitoring in order to determine possible differences between clean-air sites, industrialized city and sites in the vicinity of nuclear power plant. Samples of CO2 from the atmosphere have been collected by absorption of CO2 on the saturated carbonate-free NaOH solution for a period of 1 month under stationary conditions. The obtained Na2CO3 has been dissolved in HCl and the produced CO2 used for CH4 preparation by catalytic reaction with H2 at 450°C. A gas proportional counter filled with CH4 has been used for 14C activity measurement. The method of collection of CO2 does not require any power source and can be therefore used for sampling at the remote sites, such as mountains or forests. However, due to the lack of mixing of the NaOH solution, the absorption process is limited on the surface of the solution, and there exists the possibility of fractionation of carbon isotopes due to different reaction rate constants of 12C and 13C. A continuous record of atmospheric 14CO2 activity exists for the city of Zagreb (1986 – 2005), while shorter records (1-2 years) exist for several other sites of various characteristics: two clean-air sites (Mt. Medvednica, altitude about 1000 m a.s.l., for period 1995 – 1996, and the Plitvice National Park for period 2003 – 2005), and a site close to the Nuclear Power Plant Krško (1984 – 1986). Within the bilateral Croatian-Slovene project we have recently measured also the stable isotope composition (d13C) of Na2CO3 collected at two different sampling sites in order to determine seasonal fluctuations in both 14C and 13C isotope composition. Unexpectedly low d13C values have been obtained about (– 25± 2)‰ instead of expected (-7± 1)‰ . Such low values have been attributed to the carbon isotope fractionation during the CO2 absorption on the highly alkaline medium because of different reaction rate constants of 13CO2 and 12CO2 with OH. Since the reported 14C activities have to be corrected for the  13C content of the sample, the low d13C values of the collected Na2CO3 have to be taken into account. Therefore, our complete database on atmospheric 14C activities has been recalculated. The change of d13C from 7‰ to 25‰ increases the reported 14C activity (d14C) for 36‰ , and this difference could explain previously reported rather low atmospheric 14C activity as compared to other similar sites in Europe. In this paper we present the revised data for all sampling sites and we discuss the differences.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

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