Environmental Radioactivity in Different Climate Types: Measurement, Terrestrial Transport Process and Radiation Exposure

Abstract

The radionuclide 137Cs dose not exist naturally in the environment. Its main sources in the environment are the nuclear bomb tests, which took place mainly during 1954-1964, and the nuclear power plants accidents. The most severe accident was Chernobyl (26 April 1986). There is no record for 137Cs from nuclear bomb tests fallout (pre-Chernobyl fallout) in Jordan. So the main questions arising about the probable source of 137 Cs in Jordan are; What is the 137Cs contamination fraction due to nuclear bomb tests? Has Chernobyl affected Jordan? if yes, how large was its effect? How does 137Cs migrate in the Jordanian soils? Is it still available for the plants uptake? Is the presence of 137Cs in Jordanian soil a risk for public health? To answer these questions, two sets of soil samples were collected from pre-assumed undisturbed areas from the northwestern part of Jordan, where most of the population live. The first set of samples was collected in April 2004 from eleven different sites of area of about 10 m à ´ 10 m each, comprising 67 samples in total. The second set of samples was collected in July 2005 from six of the previous sites where higher 137Cs contaminations were found and it consists of 104 samples. The soil profiles in the second set of samples were thinly sliced for a detailed study of 137Cs profiles. The second set of samples was collected from small area ( about 10 cmà ´20 cm) that made it less representative as compared to the first set regarding the total inventory of 137Cs. The necessary laboratory preparations were performed before submitting the samples to gamma measurements. The 137Cs-90Sr ratio was used to find the ratio between 137Cs from Chernobyl and 137Cs from the nuclear bomb tests (137CsCh-137CsNB), thus a chemical separation of 90Sr was done using the so-called 'Nitric Acid Method' before submitting it to the beta measurements. Gamma measurements were done using a HPGe detector with 50% relative efficiency and 2 keV resolution at 1.33 MeV. Beta measurements were done using a gas-filled proportional detector of type Berthold Low-Level-Handprobenwechsler LB 750 L with efficiency of 21.3% cps/Bq. The specific activities of 137Cs were measured for the first and the second set of samples and the surface activities were calculated. A comparison was held between the contamination of 137Cs in the Jordanian soils and that in the neighboring countries and some countries from south, north, east, west and central Europe. The effective dose equivalent due to 137Cs in soil was calculated for the first set of samples at a height of 1 m above the soil surface in order to estimate the risk on the public health due the external irradiation. The correlations were studied between the depositions of 137Cs for the first set of samples and each of the sites average annual rainfalls and sites altitudes. The total inventories of 90Sr were measured as averages for all profiles in the first set of samples. In addition, 90Sr was measured for every layer in three profiles from the first set and one profile from the second set of samples. The mobility of 90Sr was clearly higher than that of 137Cs. In order to study the migration of 137Cs in soil, soil analysis was carried out for the second set of soil samples and two methods were applied to the measured data, namely: the 137Cs-90Sr ratio, which was applied on the first set of samples, and a convection dispersion model, which was applied to the second set of samples.