Instructions on how to build a nuclear reactor, kept safe by James Chadwick, discoverer of the neutron, were sealed in envelopes for over 70 years. Chadwick felt that the contents were "far too sensitive to publish at the time" and described as "cutting-edge science."
The envelopes contain the work of two French scientists, Hans Von Halban and Lew Kowarski, who worked in the Cavendish laboratory in Cambridge.
It reveals detailed experiments on nuclear fission, covering the components needed to make a nuclear reactor, how to create plutonium from uranium, and methods to stabilise nuclear chain reactions.
Dr Brian Cox, a particle physicist from Cern, said: "These papers describe what was cutting-edge science at the time.
"The sheer amount of knowledge that these papers contain amazes me - only eight years after Chadwick discovered that a neutron even existed, these scientists are already looking at how to use neutrons to bring about nuclear fission and energy.
