Radioactive contamination of wood and its products

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Abstract

This paper presents research on radioactive contamination of the three most common kinds of wood in Croatia — beech, oak and fir as well as acorn. Gamma-spectrometric measurements carried out on the samples of bark and wood of beech, oak, fir and acorn have shown radioactivity contents ranging from 1.6±0.1 to 37.3±0.5 Bq/kg from deposited 137Cs, whose concentrations in the soil of Croatia have increased after the Chernobyl accident. Measurements have also shown the radioactivity originating from 40K and 214Bi, which are part of the natural composition of the soil. The distribution of the radionuclides in wood has been discussed, as well as the impact of radioactive contamination of wood by the artificial radionuclide 137Cs upon the forest ecosystem. According to the corresponding model, it has been calculated that a 10 h daily stay in a typical family house increases the annual radiation dose of the population, due to the deposited 137Cs in the structure or furniture, by 343 μSv.

Introduction

Global pollution with artificial radionuclides as a consequence of nuclear experiments or accidents in nuclear plants has resulted in radioactive contamination of various degrees in certain forest ecosystems. As a consequence, apart from natural radionuclides that are usually found in the composition of soil in a habitat, artificial radionuclides are also deposited on trees. Such artificial radionuclides contaminate the habitat. The quantities of radionuclides deposited in wood depend on a number of factors related to the physiology of a live tree. However, such quantities will primarily depend upon the quantity and distribution of radionuclides in the habitat soil, from which they are transported by means of complex mechanisms in the roots and thus are deposited in the wood.

Radioactive contamination of soil in certain forest ecosystems in the Republic of Croatia, as a consequence of dry and wet deposition of radionuclides from the atmosphere, has been measured and published (Filipović-Vinceković, Barišić, Mašić, & Lulić, 1991; Barišić, Lulić, Kezić, & Vertačnik, 1992). After the Chernobyl accident, the content of 137Cs has been the most prominent. Its quantity — measured up to the depth of 26 cm — most often reaches 5–40 Bq/m2. As a result, this radionuclide will be predominantly deposited in wood and its products.

Processed wood, as building material or furniture, is permanently present in the environment of humans, and by its radioactive contamination it will contribute to an increase of the radiation rate. Wood used as fuel or in paper manufacturing will also contribute to an increase in the radiation rate received.

For the above-mentioned reasons it is necessary to determine the level of radioactive contamination of wood and its products, as well as to estimate the increase in the radiation dose in the human environment. This is the reason for concentrating, in the present paper, on research on the three most common kinds of trees in the Republic of Croatia — beech, oak and fir, both their bark and bole, as well as on the radioactive contamination of acorn.

Section snippets

Experimental

The wood samples were obtained after cutting the trees of a corresponding trunk measurement, i.e. age. At a height of 5 m above the root, an 8 cm thick piece of wood was cut. Radioactivity of samples may be considered to represent the whole trunk, while other parts of the tree may have different radioactivity, as was already measured on fir-trees (Kezić et al., 1997). After drying at room temperature, the bark was separated from pure wood. The samples of bark, wood as well as acorn were

Results

In the determination of radioactive contamination of wood there are certain difficulties in obtaining the samples because an appropriate sample can be obtained only if the whole tree is cut down. Therefore the results of research of radioactive contamination of wood in the Republic of Croatia, presented in this paper, refer to representative samples of the three largest and most frequently used kinds of trees — beech, oak and fir — as well as of acorn. A number of factors that have an impact on

Discussion

Deposition of radionuclides in wood is not the consequence of dry and wet deposition from the atmosphere being retained by the crowns of trees. As in the case of other minerals, it is the consequence of the presence of radionuclides in the habitat soil, from which they are transported by means of complex mechanisms in the roots and thus deposited in the wood.

Deposition and distribution of minerals and radionuclides in a live tree are affected by a number of factors whose interdependence cannot

Conclusion

Wet and dry deposition of artificial radionuclides results in the radioactive contamination of the soil in forests. The specific kind and rate of radioactive contamination of forest soils depends not only on the source of the radionuclides but also on their spread in the atmosphere and the migration processes of radionuclides in the soil, which are caused by various chemical and physical processes. In the assessment of radioactive contamination of the entire forest ecosystem, wood can be taken

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