The arrival of an accelerator mass spectrometer will help predict the effects of global warming, writes Anthony King
Queen's University Belfast recently received a very special delivery, a €2.05 million piece of equipment that can count atoms.
Its new Accelerator Mass Spectro-meter (AMS) is the first machine of its kind in Ireland and will be put to use within the next few weeks, according to Dr Paula Reimer, director of the centre for environment and chronology in Queen's.
The advanced device has myriad applications, she says. The AMS will help scientists understand past climate change and date archaeological sites. The machine can even identify sources of pollution and help predict effects of global warming on Irish bogs.
Ancient bones, wooden artefacts and other organic materials can be dated because a tiny fraction of carbon in the environment is radioactive carbon-14. It decays to nitrogen over a known length of time and, by measuring the amount of carbon-14 remaining in organic material, scientists can work out when the material was last alive.
AMS counts the number of carbon-14 atoms in a sample, whereas the older method counts individual radioactive emissions. "We would have spent a couple of weeks, to months, dating by the conventional method," says Dr Reimer. "With the AMS, it can process samples within hours, though pretreatment is still necessary."
"Another benefit is that we can use very small samples, less than a milligram of carbon," says Dr Reimer. "This means we don't have to destroy an artefact but can take just a small piece." The older method required 1,000 times more material.
Queen's researcher Dr Emily Murray plans to use the AMS in her research on Irish ringforts, early medieval settlement sites. These are the most common Irish monuments, yet less than 1 per cent of them have been dated.
Most seem to have been built in the seventh and eighth centuries, says Dr Murray. She hopes dating can show whether the forts are linked to an environmental downturn in the mid-sixth century. "We can't answer the question of why they were built if we can't date them. We need to get a better handle on the dates."
Trees live for hundreds of years, so a small quantity of heartwood in the bulk samples used in the older system would have skewed the results. With AMS, you can date individual seeds, leaves or bones and this ability to date individual short-lived organisms should give Murray a more precise date.
Dr Gill Plunkett of Queen's will use AMS to assess the role of solar forcing on climate change in Ireland during the Little Ice Age and Bronze Age. She dates peat sections as part of her research, but there is not enough peat in her sections for the old system.
The fact that the new system needs smaller samples will also prevent contamination. "You can have roots growing down into older peat," says Dr Plunkett. "If you can pick out the leaves you can eliminate the risk of dating something younger."
The faster turnaround time in AMS means researchers can publish their work faster, giving them a competitive advantage over other groups.
"We used to get samples back in maybe three months or more. Now we can get dates back in a few weeks," says Dr Nicki Whitehouse, a Queen's researcher interested in past climates. Also, Queen's researchers pay special rates for radiocarbon dates, which will allow for more measurements. "With more dates, the impact of our science is generally much higher," says Dr Whitehouse.
Global warming could cause peat to release more greenhouse gases into the atmosphere. With AMS, researchers can look at what happened previously when the climate heated up and see if carbon dioxide was released, says Dr Reimer. "We can also bring peat into the lab and study what happens if you keep it in warmer conditions. We can see if new or old material will enter the atmosphere."
The machine itself applies staggering forces to atoms. AMS vaporises carbon into ions, zaps them with half a million volts, and accelerates them past a magnet. "Different masses going at high velocities through a magnet curve differently," explains Dr Reimer.
She likens it to the difference between a lorry and a small car. A small car can take the corner due to its smaller mass, while the lorry shoots straight off. The phenomenon means you can ... separate isotopes of an element due to their varying number of neutrons.
AMS will help identify sources of pollution because carbon-14 is not present in material older than about 60,000 years, which includes anything made from oil. This allows scientists to say whether material in a river or landfill is modern carbon or fossil carbon.