Bomb tests help work on cold case

Dr Fiona Petchey says staff at the Waikato University laboratory are given few details about the samples they test. Photo / University of Waikato

Data from nuclear bomb testing helped New Zealand scientists pinpoint the age of a skeleton found in Australia, leading to a decades-old cold case being reopened.

The University of Waikato's radiocarbon dating laboratory helped to identify the remains of a woman found in New South Wales 45 years after she went missing.

Police have begun a homicide inquiry after the remains found in 2009 were identified as Judith Bartlett, who went missing in 1964, aged 28.

Detective Inspector Denise Godden of New South Wales police said bone was sent to Waikato because the university was able to provide the most accurate testing.

"As it turns out, the dating of the bone was very accurate and was a useful tool in the investigation."

The deputy director of the Waikato University laboratory, Dr Fiona Petchey, said lab staff were unaware of their involvement in the New South Wales cold case, as they were given limited details on samples.

But it was not unusual for the laboratory to test human bone as part of the university's work for commercial clients, including police.

Radiocarbon dating uses levels of the radioactive carbon isotope C14 in organic material to determine its age.

"Because it decays over time and does so at a set rate, it ... enables us to go directly into the sample and measure the amount of C14, and then calculate how long since that sample stopped interacting with the atmosphere," Dr Petchey said.

The age was then calibrated according to fluctuations of carbon in the atmosphere over time, she said.

Samples since 1950 were calibrated on the "bomb curve", based on changes of carbon in the atmosphere caused by nuclear bomb testing.

"In a very short period of time there was an enormous spike in C14 in the atmosphere, that transferred into the oceans and into the soil."

Atmospheric carbon levels had been constantly measured since that time, giving accurate data for carbon dating scientists to work from.

New South Wales police said samples of Mrs Bartlett's remains were also sent to Texas for DNA testing.

Scientific evidence had contributed to the conclusion her death was suspicious, but police would not reveal further details.