Carbon dating becomes more accurate

Scientists from the Australian Nuclear Science and Technology Organisation (ANSTO) and Thailand’s Naresuan University have helped to make carbon dating a more accurate chronological tool. The work was conducted by Quan Hua, Mike Barbetti, Vlad Levchenko and Andrew Smith.

The scientists explained that the use of bomb-pulse radiocarbon has become widespread as a precise dating tool for the last 60 years. Carbon-14 (¹⁴C) was generated by nuclear explosions in the atmosphere due to weapons testing in the ‘50s and ‘60s, and the resultant ¹⁴CO₂, gradually distributed throughout Earth’s atmosphere, “essentially put a mark in time”.

The atmospheric ¹⁴CO₂ level is now approaching its natural pre-bomb value. In the troposphere - the region of Earth’s atmosphere below 10,000 metres - the level of bomb-derived ¹⁴CO₂ was extremely variable in space and time. For this reason, in order to radiocarbon-date materials formed during the last 60 years, scientists need to know what those atmospheric levels were.

The researchers studied tree rings for this purpose, as the trees had photosynthesised the ¹⁴CO₂ into cellulose in their annual rings. The scientists measured the level of radiocarbon in tree rings from Thailand, Indonesia and Australia using ANSTO’s particle accelerators.

Cross-section of Thai three-leaf pine tree DIK 235/1 with rings from 1916 to 1994, from which a sub-section was used for AMS ¹⁴C analysis.

The results, together with published radiocarbon data from tree rings and atmospheric carbon dioxide samples from around the world, revealed that the level of atmospheric ¹⁴CO₂ during the early bomb period from the 1950s to the 1960s was strongly influenced by worldwide atmospheric circulation patterns.

“Using this compilation, we have been able to reconstruct regional and temporal records of atmospheric ¹⁴CO₂ levels to make carbon dating a more accurate chronological tool,” the researchers said.

“In addition, five zonal ¹⁴C data sets have been reconstructed to be used as ‘radiocarbon calibration curves’ for improved bomb-pulse ¹⁴C dating.”

ANSTO last week welcomed a $654 million federal Budget allocation over four years. This includes $76.6 million for the country’s only nuclear research reactor, OPAL, and $22.6 million to develop detailed design options for a national radioactive waste management facility.