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 identify the remains of a woman found in New South Wales 45 years after she went missing.
Police said on Monday that a homicide inquiry had been launched after the remains found in 2009 were identified as Judith Bartlett, who went missing in 1964, aged 28.
Police Detective Inspector Denise Godden said bone was sent to Waikato University 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," Ms Godden said.
Deputy director of the Waikato University laboratory, Dr Fiona Petchey, said they were unaware of their involvement in the New South Wales cold case, as they are given limited details on samples.
But it's 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 away over time and does so at a set rate, it therefore 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 is then calibrated according to fluctuations of carbon in the atmosphere over time.
Samples since 1950 are calibrated on what's known as the 'bomb curve', based on changes of carbon in the atmosphere caused by nuclear bomb testing.
"Anything post-1950 has got bomb carbon in it that stems from atmospheric nuclear bomb testing that enriched the atmosphere with C14," Dr Petchey said.
"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," she said.
Atmospheric carbon levels have been constantly measured since that time, giving very accurate data for carbon dating scientists to work from.
"We've got a very good calibration curve over the last 60 or so years that enables us to give a precise date for anything that has lived between about 1950 and present day."
Levels of atmospheric C14 have been declining since atmospheric nuclear testing was banned in the mid-1960s, Dr Petchey said.
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 release further details.
- By Heather McCracken of APNZ
