This technique is more sensitive than gamma spectrometry and is suitable when a small quantity of sample is available for analysis.However the method is destructive and other radionuclides such as Pb dating can be undertaken by gamma spectrometry technique.Please discuss your proposal with the appropriate ANSTO Contact Scientist before submitting your proposal as they will assist you in making the correct capability selection.Pb activity (half-life = 22.3 years) to determine the rate of sediment accumulation.This gas produces 210Pb by decay in the atmosphere.The lead isotope enters the earth’s crust or the water through precipitation.In addition to the mentioned rates, the dating may also give a picture of the stability of the sediments and thus tell whether the chronology of the layers is intact or whether the activity of the benthic fauna has changed the chronology by bioturbation.Local changes of current conditions may also cause changes of the chronology of the layers.
The sediment samples must remain totally undisturbed during sampling to obtain the best possible dating.
Furthermore, the 210Pb method may be used to carry out a sensitivity analysis to estimate the suitability of the sediment to repeated monitoring of, for instance of changes in the flux of contaminants in the sediments.
Pb against depth or cumulative weight (to allow for compacting) will be a straight line if the sedimentation rate has been constant.
The samples are simply packed into petri dishes or vials, left to equilibrate for three weeks and then counted on a High Purity Germanium (HP-Ge) gamma spectrometry system.
In the series of unstable products from the radioactive decay of uranium-238, lead-210 results from the decay of radon-222 and is a precursor of the stable isotope lead-206.