遇见地球上20亿年前已知天然核反应堆——奥克洛

Rock samples from Oklo, some of them recovered during drilling campaigns, are stored in the headquarters of France’s nuclear power and renewable energy company Orano. In early 2018, two half split drill-core samples were donated to Vienna’s Natural History Museum. The donation was made possible by the financial contribution of Orano and France’s Alternative Energies and Atomic Energy Commission (CEA), with the support of the French Permanent Mission to the United Nations and the International Organizations in Vienna. IAEA scientists helped when the sample was delivered to Vienna by monitoring radioactivity levels and facilitating the rock’s safe handling.

The two samples emit a radiation of approximately 40 microsieverts per hour if you stand 5 centimetres away from them, which roughly compares to the amount of cosmic radiation a passenger would receive on an eight-hour flight from Vienna to New York. The museum, which receives 750 000 visitors a year, is used to dealing with radioactive samples since it already displays a number of slightly radioactive rocks and minerals.

“We want people to learn about natural radioactivity, to make them aware of the fact that radioactivity is all around us, that it’s natural and that at low levels it’s not dangerous. Radioactivity is in the floors and walls of our homes, in the food we eat, in the air we breathe, and even in our own body,” said Ferrière. “What better way to explain this than by showing a real sample from Oklo, where nuclear fission occurred naturally billions of years ago?”

The permanent exhibition will show different sources of background radioactivity. Perhaps a world map with the distribution of radioactivity, a radiation detector or Geiger counter or a cloud chamber, will allow visitors to see exposure to natural radiation for themselves.

“Rocks are like books. You can look at the cover and get some basic information, but it’s when you open them that you get the full story,” Ferrière said.