鈥淭he paper is such that it would be inadvisable to publish it at the present time.鈥� So ends a yellowed note dated 18 December 1941 from James Chadwick to the UK鈥檚 Royal Society. The note was attached to a batch of papers written by two French physicists, Hans Halban and Lew Kowarski. What was Chadwick, the discoverer of the neutron, so concerned about, and why did the Royal Society heed his request and seal the papers?
To mark the 75th anniversary of Chadwick鈥檚 discovery of the neutron, the Royal Society has now broken the seal and revealed that the papers outline the design of a nuclear fission reactor and ways of initiating a chain reaction. Given that continental Europe was already under Nazi control, this was explosive material.
The papers were discovered nine months ago in a box on a shelf in the Royal Society鈥檚 archives as part of an ongoing cataloguing project. 鈥淭hey are the only sealed papers ever discovered in our archive,鈥� says Keith Moore, the society鈥檚 head of library and archives.
Advertisement
Along with Frederic Joliot, Halban and Kowarski had been part of the French nuclear programme working on ways of controlling fission reactions. On the eve of the second world war, Joliot bought 26 drums of heavy water 鈥� the world鈥檚 entire stock 鈥� from the Vermok hydroelectric plant in Norway. Heavy water contains the isotope deuterium instead of hydrogen. The researchers believed they could control fission in a reactor, or 鈥渂oiler鈥�, containing heavy water.
When the Nazis invaded France, Joliot instructed Halban and Kowarski to smuggle their work and the stash of heavy water to England. The pair arrived in Falmouth, Cornwall, on board a steamer in early 1940, and shipped their precious cargo first to Wormwood Scrubs prison in west London, and then to Windsor castle in Berkshire for safety. Halban and Kowarski were finally taken on at the Cavendish Laboratory in Cambridge, where the heavy water eventually joined them, and here they wrote up their sensitive work.
The papers include one entitled 鈥渢echnological aspects of nuclear chain reactions used as a source of power鈥�. 鈥淭hey show a clear understanding of all the crucial aspects that allow fission reactions to occur,鈥� says John Hassard, a nuclear physicist at Imperial College London. 鈥淲hat I find staggering is how quickly they made progress in those days. This is barely a decade after the discovery of the neutron. At the very least, this is a brilliant summary of the state of the work at the time.鈥�
鈥淭hey show a clear understanding of all the crucial aspects that allow fission reactions to occur鈥�
To ensure that the papers didn鈥檛 go astray, Halban and Kowarski sent them to a number of people to deposit them at the Royal Society. One batch was sent to the nuclear physicist Patrick Blackett. In a handwritten note to the Royal Society, Blackett wrote, 鈥淥wing to the necessity of secrecy, they couldn鈥檛 be published and yet Joliot, with whom Halban and Kowarski were working, wanted so to speak to reserve priority rights.鈥�
Jeff Hughes, a historian of science at the University of Manchester, UK, says these comments show that the French scientists were keen to protect their intellectual property. 鈥淭hey clearly wanted to make sure the French got the recognition for the work.鈥� Last week Hughes did a preliminary check in the UK鈥檚 National Archives and found copies of all but one of the sealed papers there. It is likely no one noticed their significance until now. The archives also contain a series of patent applications by Halban and Kowarski outlining designs for a fission reactor.
Halban left the UK during the war to direct the British-Canadian fission reactor project in a new lab set up near Montreal. Kowarski stayed at the Cavendish Laboratory until 1946, after which he returned to France to join its nuclear power programme.
UK intelligence agency MI6 kept a file on Kowarski, as he was known to be left-leaning and a friend of fellow Cambridge physicist Alan Nunn-May, the scientist-turned-spy who stole secrets from the British and American atomic programmes and gave them to the Soviets. However, although there were various allegations about his loyalty, MI6 never did establish his political affiliations.
