Thursday, 30 September 2010

Nuclear archaeology

Nuclear Physics can help in the world of archaelogy, helping to understand artefacts created long before humankind knew anything about atomic nuclei. I heard a story on Radio 4's Today programme yesterday about the discovery of the skeleton of a bronze age teenage boy near Stonehenge who came from the Mediterranean.

The story mentioned "geochemical" analysis, but the main interviewee mentioned nothing about the nuclei behind the story. What they really discovered was that the isotope ratios of both Oxygen and Strontium isotopes were more characteristic of someone growing up in a Mediterranean environment than a British one.

Heavy oxygen isotopes in water molecules tend to fall more readily as rain when a cloud is cooling, and when it gets colder and colder it tends to be more and more depleted in heavy oxygen. The ratio of Oxygen-18 to Oxygen-16 can be used therefore as a reasonable guide to temperature (and it is used, for example, in measuring the historical temperature of the earth by looking in ice cores from Greenland).

By looking at the oxygen isotope ratio in tooth enamel, which is grown during childhood, evidence of the climate one experienced while growing up can be found.

The other clue comes from the presence of Strontium. Strontium occurs all over the world in ores, but its occurrence, like with all elements varies across the world as a result of chance geological events. Strontium makes its way into the local food chain and then substitutes for calcium in bones, it being in the same chemical group of the periodic table. Looking at the strontium isotopes can then be correlated with where one grew up. This all adds up to the ability to determine where a boy from 1550 BC grew up!

More details can be found on the British Geological Survey's website.