By Paul Rincon
BBC News Online science staff, at the BA festival
A new approach to measuring radioactive isotopes in bones could transform the way forensic pathologists determine the ages of skeletal remains in future.
Isotopes could mean more accurate dating of remains
The novel test uses an isotope, or form, of lead, with a so-called half-life (the decay rate) of 22.3 years.
Forensic anthropologists can use this property to pinpoint the exact year of death many decades in the past.
The dating technique is being discussed this week in Exeter at the British Association's Festival of Science.
Scientists have put special detectors on living people to study the content of the isotopes in their skeletons, to set a benchmark that can be employed for better dating of corpses.
"If you know the concentration of bones in the living, you can work out how long it is since a person died," said Professor Stuart Black, of the University of Reading.
The lead isotope concerned is called 210Pb and is absorbed by humans in their food.
"Although we differ in diets, we all have the same concentrations in our bodies because basically all foods have roughly the same concentrations of these isotopes," said Professor Black.
When a person stops eating, the isotope starts to decay and diminish. The half-life is the period over which one half of the original population of radioactive atoms in a sample takes to decay.
So by establishing the 210Pb deficit in a corpse, scientists can determine to within a year the time of death.
Professor Black said the lead technique was already being used by UK forensics teams, and the US Federal Bureau of Investigation had apparently shown interest in its application, too.
Professor Black is also investigating a similar technique using an isotope of the element polonium.
This isotope, 210Po, has a much shorter half-life of 138 days. It would pinpoint time of death on the scale of weeks.
He said it might be more reliable than current methods which rely, for example, on insect activity in the corpse.
Professor Black said these were affected by variations in temperature, season, and uncertainties in how the person died. This can lead to large inaccuracies and, currently, any estimates using this method produce only broad timeframes.