Aisling Irwin reports from the annual meeting of the American Association for the Advancement of Science in Atlanta. High-tech neutron techniques are being used by archaeologists to examine ancient societies - by distinguishing between objects used less than a kilometre apart from each other.

The process involves bombarding a substance with neutrons. Atoms are transformed into radioactive nuclides which emit gamma rays with an energy characteristic of the molecule.

As a result, tiny impurities in ancient materials, such as clay pots, can be pinpointed to a small area.

James Blackman, senior research chemist at the Smithsonian Institution recently worked on a site in south western Iran, populated by a people between 3200bc and 2800bc.

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There was a mound containing the remains of highly decorated buildings and artefacts such as jars and writing tablets with large numbers enscribed on them. There were also other buildings at the bottom of the mound - with jars of small ornaments and tablets with small numbers on them. The archaeologists wanted to know whether goods were moved.

Dr Blackman analysed the clays and found that they differed.

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He found that jars were made on the individual sites and never moved. Tablets from the low ground were always made there as well. But the high mound contained tablets that originated from both high and low areas.

Dr Blackman says: "Information was flowing from one area to what was probably an administrative centre." This proved the existence of an early state.