Cases and solutions Environmental Geology 32 (4) November 1997 7 Q Springer-Verlag 281 Received: 31 January 1997 7 Accepted: 11 March 1997 N. S. Abu-Jaber (Y) 7 A. Jawad Ali Department of Earth and Environmental Sciences, Yarmouk University, Irbid 21163, Jordan E-Mail: abujaber6yu.edu.jo B. A. Al-Bataina Department of Physics, Yarmouk University, Irbid 21163, Jordan Radiochemistry of sediments from the southern Dead Sea, Jordan N. S. Abu-Jaber 7 B. A. Al-Bataina 7 A. Jawad Ali Abstract A sediment core from the southern Dead Sea was analyzed using gamma spectroscopy as well as 210 Pb dating in order to ascertain if any ra- dioactive contamination could be detected and to determine the sedimentation rates in the area. Re- sults of this study show no presence of man-made radionuclides in the area. Sedimentation rates were determined to be between 0.25 and 0.4 g/cm 2 /year. (F0.5 cm/year), which is in line with what would be expected assuming carbonate layers are annual varves. Key words Dead Sea 7 Dimona 7 Jordan 7 Radiochemistry 7 210 Pb dating Introduction The issue of radioactive contamination in southern Jor- dan has recently become a focus of popular concern. This is largely due to the proximity of the Dimona Nuclear Power Plant (NPP) in southern Israel. The secrecy sur- rounding this site and press reports highlighting safety problems associated with the storage of the waste prod- ucts has caused speculation about leakages from the reac- tor. Additionally, high concentrations of naturally occur- ring radon in the Jordan Valley Rift area have recently been documented (Steinitz and others 1992). The source of this gas is believed to be from deep-seated faults. The purpose of this study is to evaluate the nature of the radioisotopes present in the study area near the Dimona NPP. A sediment core from the southern Lisan Bay area in the southeastern corner of the Dead Sea was taken in order to evaluate whether measurable concentrations of fission products and uranium daughters have been incor- porated into the sediments of the area throughout the length of time represented by the sediment core. This time was evaluated by radiochemical techniques, specifi- cally by 210 Pb dating. 210-Pb dating The use of 210 Pb to date sediments ranging from a few years up to 100 years is a common tool in modern ocea- nographic (Nittrouer and others 1979) as well as limno- logical studies (Bollhofer and others 1994). Sediments in modern marine and lacustrine environments accumulate 210 Pb in two ways. In part 210 Pb is derived from the 238 U decay series, due to the presence of the parent isotopes, specifically 226 Ra within the sediment. 210 Pb from this source quickly reaches secular equilibrium with the 226 Ra in the sediment, and remains constant at the time scale of interest to this type of study. 210 Pb from this source is termed “supported”, as opposed to the second source, which is derived due to the decay of 222 Rn in the atmo- sphere. As 222 Rn decays, 210 Pb is formed. Subsequently the 210 Pb adheres to clay particles present in soils or in suspended sediments in water bodies. This 210 Pb is “un- supported”, and subsequently decays at a rate propor- tional to its half-life of about 22.5 years. This unsup- ported 210 Pb is commonly termed excess 210 Pb and is the basis of dating sediments and determining sedimentation rates in modern marine and lacustrine environments. Differentiating between supported and excess 210 Pb is simply a matter of monitoring where 210 Pb becomes con- stant with depth in a core. This constant rate of 210 Pb ac- tivity is the supported 210 Pb, and the excess 210 Pb is thus the difference between total and supported 210 Pb activity. Study area The Dead Sea occupies the lowest point in the Jordan Valley Rift system (JVR). The JVR is a major left-lateral transform fault which separates the Arabian and African crustal plates, and constitutes the continuation of rifting of the Red Sea. This system has led to the formation of a series of downfaulted blocks, thus leading to the descrip-