A bottle discarded at a waste site in the US contains the oldest sample of bomb-grade plutonium made in a nuclear reactor, scientists say.
The sample dates to 1944 and is a relic from the infancy of the US nuclear weapons programme.
The type of plutonium in the bottle - known as Pu-239 - is a so-called alpha emitter. These alpha particles are too bulky to penetrate skin or paper, but they can cause poisoning if swallowed or inhaled.
It has a half-life (the time it takes for half the radioactive nuclei in a sample to decay) of 24,110 years.
The bottle in question was discovered in a burial trench at the Hanford nuclear site in Washington state, north-western US.
Established as part of the Manhattan Project in 1943, Hanford was home to the world's first full-scale plutonium production facility.