Determination of Depleted Uranium in Environmental ...

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suitable and inexpensive biological detectors of the fallout pattern [5]. ... Sector 54-30 TIMS equipped with nine Faraday cup collectors and a Daly ion-counting.
Determination of Depleted Uranium in Environmental Bio-monitor Samples and Soil from Target sites in Western Balkan Region Sarata K. Sahoo", Hiroko Enomoto", Shinji Tokonami", Tetsuo Ishikawa", Predrag Ujic'', Igor Celikovic'' and Zora S. Zunic'' "National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan Institute of Nuclear Sciences „ Vinca, Mike Petrovica Alasa 12-14, 11000 Belgrade, Serbia Abstract. Lichen and Moss are widely used to assess the atmospheric pollution by heavy metals and radionuclides. In this paper, we report results of uranium and its isotope ratios using mass spectrometric measurements (followed by chemical separation procedure) for mosses, lichens and soil samples from a depleted uranium (DU) target site in western Balkan region. Samples were collected in 2003 from Han Pijesak (Republika Srpska in Bosnia and Hercegovina). Inductively coupled plasma mass spectrometry (ICP-MS) measurements show the presence of high concentration of uranium in some samples. Concentration of uranium in moss samples ranged from 5.2 - 755.43 Bq/Kg. We have determined ^''U/^'^U isotope ratio using thermal ionization mass spectrometry (TIMS) from the samples with high uranium content and the ratios are in the range of 0.002097-0.002380. TIMS measurement confirms presence of DU in some samples. However, we have not noticed any traces of DU in samples containing lesser amount of uranium or from any samples from the living environment of same area. Keywords: environmental radioactivity, uranium, depleted uranium, mass spectrometry. PACS: 29.25.Rm

INTRODUCTION Uranium is a naturally occurring radioactive element present in Earth's crust, depending on the geological location, its concentration in surface soil varies from 0.1 mg kg"^ to 20 mg kg"^ (activity 35 Bq Kg"^) [1]. The natural abundances of three long234

235

238

lived primary isotopes of U, U and U are approximately 0.0054%, 0.720% and 99.275 % respectively. However, DU is a by-product of the manufacture of enriched 235

238

uranium for use as a fuel in nuclear reactors and nuclear weapons. DU has a ""U/"°U atomic ratio up to -0.002. During Military conflicts in Kuwait and Iraq (1991), Bosnia (1995) and Kosovo and South Serbia(1999) approximately 330 tons of depleted uranium (DU) munitions were used [2]. The type of ammunition employed contains a conical DU "penetrator" 95 mm in length and with a base diameter of 16 mm, weighing approximately 300 g. As per NATO, about 9 tons of DU munitions were fired around 112 locations in Kosovo [3] and around 1.5 tons in South Serbia (Bratoselce, Reljan, Barovac). Most penetrators are thought to have missed targets. On the other hand, when DU penetrators hit hard targets or when DU metal bums, DU aerosols or dust particles are formed, which can be dispersed into the environment, with the risk of contaminating the surrounding soil and CP1034, The Natural Radiation Environment—S International Symposium, edited by A. S. Paschoa © 2008 American Institute of Physics 978-0-7354-0559-2/08/$23.00

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vegetation. Thus, knowledge of the uranium isotopic composition is important to clarify the possible origin of uranium. Lichens have been reported to accumulate a variety of radioactive and stable elements. The radiological interest in lichens as bioindicators of radioactive fallout originates from the period of atmospheric nuclear tests. Long-lived radionuclides, such as Cs, Sr and Pu contributed significantly to the radiation burden of people living on reindeer meat as a result of the lie hen-reindeer-man food chain [4]. Chernobyl nuclear accident renewed interest in the behavior of Cs and suggest that lichens are suitable and inexpensive biological detectors of the fallout pattern [5]. However, there are a few studies available on the determination of uranium concentration or its isotopes in lichen samples from contaminated areas [6]. This paper reports determination of uranium and its isotopes from soil and lichen samples collected from first targeted site in Balkan region in 1999, Han Pjesak (FIG 1) using ICP-MS and TIMS. It is possible to measure ^U not only in soil samples but also in lichen samples.

MATERIALS AND METHODS Samples and sample preparation The samples selected were lichens belonging to different species, sometimes with bark on which they grow, moss and uppermost layer of soil. All samples were collected from Han Pijesak in April 2003 and its location is presented in Fig. 1. MU MGARY CROATIA^

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