ENVIRONCHRON, INC.
TALLAHASSEE, FLORIDA

By using multiple isotopes, each acting as unique environmental indicators and each with separate qualifying characteristics, provides for in-depth and credible assessment of sedimentary dynamics. : 137Cs, with a half-life of 30.3 years, is a thermonuclear byproduct.  Its presence is directly related to the atmospheric testing of nuclear devices during the latter half of the 1950’s and early 1960’s.  With the exception of the Chernobyl failure and the Indian/Pakistani tests, there has been no cesium-137 released to the atmosphere since the cessation of atmospheric nuclear testing. These events produced minor amount of cesium-137 when compared to the nuclear testing of the sixties. Many investigators use cesium-137 exclusively as a dating tool.  They measure cesium-137 in sediment and assume highest measured value is result of the maximum fluxes between 1962 and 1965. Due to difficulties in sample and sampling resolution the peak value is assumed be correspond to 1963 ± 2 years.  They use this as a “dated” horizon and calculate a sedimentation rate from this value.  In some marsh sediments, this isotope has been demonstrated to be mobile and thus not a good isotope for “dating” purposed.  However, in clay systems, it is conservative and meets criteria #5. 137Cs is a byproduct of thermonuclear weapons testing.  The graph shows that fallout in Miami, Florida was present as early as 1952.  Peak fallout is accurately represented in the study core in 1963, the peak ot thermonuclear weapons testing.  Note that natural mixing phenomenon account for not ideal representation of a fallout curve. 210 Pb, with a half-life of 22.8 years, is ideal for most ecosystem studies, where changes have occurred within the last century.  A member of the 238U series, lead-210 is subject to disequilibria with its distant relative radium-226 (226Ra) due to the physio-chemical activity of the intermediate gaseous progenitor radon-222 (222Rn). Radioactive disequilibrium arises when the gaseous radon-222 escapes into the atmosphere.  With a half-life of 3.8 days, the radon-222 decays through a series of very short half-life isotopes to lead-210. This process produces excess lead-210 in the atmosphere and subsequently the hydrosphere. Like berylium, the highly reactive lead is rapidly adsorbed to or incorporated on particulate material. Precipitation of this material produces excess lead-210 over lead-210 in equilibrium with ambient 226Ra already in sediments.  This excess lead-210 provides the mechanism for age and depositional assessment.  (More :