DSpace at VNU: Long-lived unstable nuclei as microindicators for some processes of nature

120, 33175 Gradignan, Cedex, France ‘Faculty of Nuclear Physics, University of Natural Science, 334 Nguyen Trai, Thanh Xuan, Hanoi 137Cs and gOSr are the long-lived radioactive isotopes

ELSEVIER Nuclear Physics A722 (2003) 528c-53 lc

www.elsevier.com/locate/npe

Long-lived unstable nuclei as microindicators for some processes of nature

Ph Hubert’, F Hubert’, H OShumii, Q.H Pharni,’

‘Centre d’Etude Nucleaire de Bordeaux, Gradignan (CENBG), Domain du Haut

Vigneau, BP 120, 33175 Gradignan, Cedex, France

‘Faculty of Nuclear Physics, University of Natural Science, 334 Nguyen Trai, Thanh Xuan, Hanoi

137Cs and gOSr are the long-lived radioactive isotopes generated from nuclear tests/acciden These isotopes take part in various processes of nature

R.adioactivities due to these isotopes in environmental samples relate closely not only

to date, site, characteristics, etc of nuclear tests/accidents, but also to mechanism of processes in which the isotopes are presented

Determination and analysis of 137Cs and g”Sr radioactivity of environmental samples would disclose interesting information of some natural processes and other relating issues

In this paper the following topics will be discussed:

1 The radial distribution of 137Cs and “Sr in annual tree rings

2 The relation with accumulative deposition of radioactive fallout

3 What would be the mechanism of internal transfer processes during tree aging

1 INTRODUCTION

Cesium is an artificial isotope generated from the nuclear tests/accidents, it is one of thousands of unstable nuclide known so far The half-life of 137Cs is 30 years, so this long-lived isotope diffuses in nature, goes into the soil through rain and transfers to trees

by metabolism processes Each Gee-ring is one year of tree’s life 137Cs concentration

is different in different tree-rings This variable law depends on various environmental factors, on metabolism processes in trees and on other processes of nature [I] The distribution of isotopes and trace elements in tree rings is not only telling us something about environment but also about processes taking place in trees and tree rings

In this article the distribution of 137Cs in tree rings is discussed in relation to the processes taking place in trees and to the accumulative deposition of radioactive fallout

2 EXPERIMENTS

A trunk of Cryptomeria japonica D Don (Japanese name, Sugi) was sent from Japan

to Center for Nuclear Research in Bordeaux Gradignan (CENBG), France Samples were the pieces cut from this trunk Sectioned wood (2cm thickness and 7cm diameter) of 30 - 40g dry weight was subjected to analysis for 137Cs Each sample composes of about 15 +

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20 or more tree rings The samples were cleaned, dried and kept in the polyetylen bags The 137Cs concentration presented in Bq/kg wood were calculated from the 662keV peak’s area of the gamma spectrum measured by the low background gamma spectrometer

in CENBG [l] The set up of this spectrometer is presented in Figure 1

3 RESULTS AND DISCUSSION

The Figure 2 presents the distribution of 137Cs concentration in the tree rings from the inner ring to outer one The most inner ring of the trunk is the oldest The extra high value of 137Cs concentration indicates that the metabolism mechanism in the back

is different from other parts of the trunk This high value could be attributed to ls7Cs directly deposited on the surface of the back

The annual deposition from “Radioactivity Survey Data in Japan” and nuclear explo- sion tests in air from Carter & Moghissi (1977) and Carter (1979) presented in Figure 2 show the correlation between the distribution of 137Cs concentration in the tree rings and the radioactive fallout

137Cs is clearly observed in the tree rings formed before 1945 when the first huclear weapon test was conducted No correlation was observed between 137Cs in individual tree rings and the radioactive fallout This result was also published by Masuchika et al (1988) [3]

The distribution of “Sr and 137Cs in annual tree rings of Sugi was studied by Mo- moshima et al (1994) The authors suggested [l] that the mobility of 137Cs is higher than “Sr The radionuclide 137Cs probably moved in rays of the wood xylem It is rea- sonable Cesium belongs the group I and Strontium - group II of the Periodic Table of the elements To study any possible correlation between variation of 137Cs concentration in tree and radioactive fallout, a set of samples of various French wines with wintage years ranging from 1950 to 1998 has been analyzed by Hubert ed al [2] In the figure 2 the 137Cs concentration in French wine with wintage years are presented

There are a good correlation between 137Cs concentration in wine and radioactive fall- out It is clear that grapes absorbed directly fallout

4 CONCLUSION

The distribution of Cesium and Strontium in tree rings or various parts of tree are different The difference depends on the chemical property of each element

Both two radioactive isotopes 137Cs and “Sr are usually used to study environmental radioactive, but the correlation between the distribution of these isotopes and radioactive fallout does not appear the same

REFERENCES

1 Momoshima N., et al., J Environ Radioactivity 22(1994)93-109

2 Hubert et al., private publication, 2001

3 Masuchika K., et al., J Environ Radioactivity 8(1988)15-19