Radioactive lead, 210 Pb, measured in lake sediments, is used to date relatively recent environmental records (from present until the start of the Industrial time) as the 210 Pb radionuclide has a relatively short half life of about 22 years. The 210 Pb content of lake sediments is deriving from two sources: 1) The 222 Rn (half-life 3.83 days) decay, a daughter isotope of 226 Ra (half-life 1622 years), within the sediment column and 2) An excess source deriving from the atmospheric fallout of 210 Pb. In the absence of atmospheric 210 Pb fallout, 210 Pb will be in radioactive equilibrium with the radium isotope 226 Ra in the sediment. Two different models are applied to calculate the age of the sediment dependent on a constant or varying sedimentation rate.
(See e.g. P.G. Appleby & F. Oldfield, 1983. The assessment of 210 Pb data from sites with varying sediment accumulation rates, Hydrobiologia 103, 29-35.)

In the NORPEC project, five short sediment cores from five alpine lakes in a west-east transect in Southern Norway have been sampled by a Renberg corer and sliced into 2.5 mm sections. These cores are 210 Pb dated at the Environmental Radioactivity Research center, at the University of Liverpool by Peter Appleby. These cores are part of the Little Ice Age project within NORPEC where we look for diatom responses to environmental changes during the last 500 - 1000 years.