**4. Conclusions**

220 Radioisotopes – Applications in Physical Sciences

convection velocities resulted rather higher when compared with the data of temperate regions from Chile [Schuller et al., 1997], while the diffusion coefficient was close to those

Fig. 9. Diffusion coefficient (*De*) and convection velocity (*ve*) parameters together with the

The present set of transport parameters of 137Cs in soils is presented in Fig. 9. A scatter is observed in the data. Most of Argentinean diffusion coefficient data are slightly larger than the average values reported by IAEA for weapon test fallout [IAEA, 2010] while the Chilean data fit quite well with the average values with the exception of CS3, CS4 and CS43. Concerning the convection velocity parameter, the determined values from Provincia de Buenos Aires-Argentina soils resulted close to the worldwide average ones [IAEA, 2010], while those determined in the San Luis Province-Argentina are higher than the IAEA data [IAEA, 2010]. In Chile, the values were lower than the worldwide average [IAEA, 2010], being some of them negative, probably related to the periodic flooded lowland. Several mechanisms, such as bioturbation, horizontal transport, transport through macropores, migration of suspended particles, etc., have been used to explain the deviations from the convection-dispersion predictions, putting the ODCDE model under consideration and suggesting that the model is an oversimplification of such a complex process. However the ODCDE model is very useful to estimate the transport

obtained in the Antarctic region [Schuller et al., 2002].

IAEA (dash line) [IAEA, 2010].

parameters.

A systematic compilation of radionuclide activity data in soil of South America has been completed. Radionuclide activity data concern to the natural 40K, 238U and 232Th chains, and to the anthropogenic 137Cs nuclides.

The surface activity concentrations for 238U for Brazil and Argentina are higher that the worldwide mean values. The 232Th activity data of Argentina are closer to the worldwide values while the Brazilian ones are quite higher than the worldwide values. In the case of Uruguay, it is not possible to extract conclusions yet due to the insufficiency and dispersion of data. The 40K data are higher than the mean values in most of the cases, and fit into the worldwide range with some exceptions. The annual committed effective terrestrial exposure dose for infants, children and adults have been calculated, resulting the values slightly higher than the UNSCEAR value in the case of adults. The analysis of the 137Cs inventories allows concluding that the experimental data do not follow the latitudinal band deposition predictions proposed by UNSCEAR. It is worth to mention that the analysis of the whole set of information in South America allows to establish a correlation between the inventory and the annual precipitations. Different shape type profiles have been determined for Argentina, Brazil and Chile. In several cases it was possible to reproduce the 137Cs profiles with models accounting diffusion and convection process. The transport parameters agree well with the average worldwide values due to nuclear weapon test fallout. Some discrepancies were detected when bioturbation and floodedland are present, indicating that efforts to include these processes should be done to fully reproduce the caesium profiles, hence to be able to make predictions of migration in case of possible pollution.

The present set of data contributes to the establishment of regional baselines as well as help in the development of local regulations concerning to permitted activity limits to people health protection.

#### **5. Acknowledgements**

Research grants PIP 0230 from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina) and PICT 38047-Préstamo BID from Agencia de Promoción Científica (ANCYT, Argentina) are gratefully recognized.

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**12** 

*Mexico* 

**Radioactivity in Marine Salts and Sediments** 

Manuel Navarrete, José Golzarri, Guillermo Espinosa, Graciela Müller,

Radioactivity is a natural phenomenon always taking place in our planet and in the whole universe. In the very beginning of matter, which it is evolving till now, some radioactive isotopes were created, among others, to form either in a mixture or as a single one, the ninety material units known as elements, which combined in a huge number of ways represent what is called matter, nature and universe. This sort of radioisotopes are, for example, 40K, 50V and 87Rb, as well as every radioisotope found from bismuth to uranium, all of them radioactive, classified by Mendeleieff according their atomic number and weight in the Periodic Chart. These natural radioisotopes are called Primordial and are

Radioisotope Half Life (years) Isotopic Abundance (%) K 1.3x10**9** 0.0118 V 6x10**15** 0.24 Rb 4.7x10**10** 27.85 Cd 9x10**10** 12.3 In 6x10**14** 95.72 Te 1.24x10**13** 0.87 La 1.3x10**11** 0.089 Nd 2.1x10**15** 23.85 Sm 1.1x10**11** 15 Sm 7x10**15** 11.2 Gd 1.1x10**14** 0.20 Dy 2x10**14** 0.06 Lu 3x10**10** 2.6 Hf 2x10**15** 0.18 Re 5x10**10** 62.6 Os 2x10**15** 1.6 Pt 6x10**11** 0.0127 Bi > 2x10**18** 100 Table 1. Radioisotopes in the isotopic mixture of elements from K to Bi (Primordial)

**1. Introduction** 

shown in Table 1.

(Choppin a, 1980)

*National University of Mexico/Faculty of Chemistry/Institute of Physics* 

Miguel Angel Zúñiga and Michelle Camacho

