1. Chernobyl derived 137 Cs in the soils of Israel, 2005. Ehud Ne’eman 1, Joel Kronfeld 2, Victor Steiner 3, Dorothy I. Godfrey-Smith 4 1 Holon Technological Institute, Holon, Israel, 2 Department of Geophysics and Planetary Sciences, Tel-Aviv University, Ramat Aviv Israel 3 Noise and Radiation Abatement Division, Ministry of the Environment, Israel 4 Radiological Analysis and Defense, Defense R&D Canada-Ottawa, Canada, K1A 0Z4 The radioactivity released by the Chernobyl-4-reactor accident has been widely studied in Europe. Much less is known about the contamination of the southern Levant countries The gamma-ray emitting 137 Cs and the shorter lived 134 Cs were among the most important radio-nuclides of concern owing to their high relative abundance and biochemical affinities. The radioactive plume arrived over Israel in May 2, 1986. Though surveys were immediately carried out to ascertain the extent of the contamination pertaining to public health (Schlesinger et al, 1996,IAEA paper # IAEA-CN-63/351), the amount of environmental data published concerning the behavior and distribution of radio-cesium in Israeli soils has been limited. The present study is the first to present relatively widespread coverage of the behavior of radio-cesium from various soil types in depth profiles from Israel. We present how 137 Cs has redistributed itself over the past 19 years. Representative high resolution gamma-ray spectrum of the HP Ge 80 % efficiency detector. Though the health concerns pertaining to radiation from 137 Cs in Israel is minor, this study has implications for areas that were more seriously affected. The majority of the radio-cesium in the soil has been displaced downwards. The surface radiation and thus the external 137 Cs dose rate is found to decrease faster than dictated by the rate of radioactive decay, governed by its half- life. This is due to such effects as the erosion of the soils, uptake by vegetation, and by significant migration downwards, as is seen in this study As the external radioactive dose rate is attenuated exponentially as a function of thickness of the overlying soil, the downward migration (irrespective of the other factors), significantly mitigates the original surface dose rate. Moreover, it is not possible to meaningfully reconstruct the initial amount of soil contamination once a significant time period has elapsed as is the case in this study, because of these factors. Spatial and temporal distribution of the radioactive cloud over the northern hemisphere. The arrival of the cloud over Israel was accompanied by an unseasonable, intermittent drizzle that sporadically deposited the fallout in uneven patches over the country. Initial Chernobyl release: 134 Cs / 137 Cs = 0.5 These gamma-emitting nuclides are readily measured by HP Ge detector coupled to a gamma-ray spectrometer. Preliminary studies of surface soils in Israel at the time of the accident did note this characteristic activity ratio, which can not be seen today as the short-lived (2.08 yr half-life) 134 Cs nuclide has died away by 2005.Today only the 137 Cs (30 yr half-life) is noted. 2 1 1 2 2 3 4 4 5 6 7 8 9-12 13 14 15 16-17 depth cm 5 25cm depth Bq/Kg depth (cm) Bq/kg 5 Kerem Shalom Kurkar Sands (not detected) 4 Rafiach Kurkar Sands 137 Cs Bq/kg 2 3 1 Sample Locator map- showing sites where the soils were obtained. The thickness of the soils over most of the country is quite limited due to historical events that resulted in extensive of soil erosion. Along side the map are the radiometric analyses of 137 Cs (dry weight) as a function of depth, for the year 2005. Large variability in the concentration of radio-cesium from site to site is seen not only at the surface but at the rate at which the cesium has migrated downwards through the soil profile. For example, in the Ramot Eshkol suburb of Jerusalem the surface ( 0-5 cm) radio-cesium ( solely 137 Cs now) was 53 Bq/kg and had declined to only 40 Bq/kg by 10-15 cm through the chalky marl. In comparison, samples from a terra rosa soil of the Beit Safafa, suburb, having a similar surface radioactivity, of 49 Bq/kg, had exhibited a 137 Cs gamma-ray activity of only 3 Bq/kg at the 10-15 cm depth interval. On the other hand, in the hamra soils of the coastal plain by the city of Hadera, the 10-15 cm interval was found to have a greater 137 Cs activity than the two overlying intervals (0-5 and 5-10 cm) combined.