B.G. Harvey at CRNL (Photo from the Empire Digest, June 1948)
The files of the Canadian Nuclear Heritage Museum (CNHM) contain a copy of the minutes of a meeting held to discuss nuclear physics experiments at the Montreal Lab December 13, 1944. The meeting was chaired by chaired by John Cockcroft. A note at the top of the document states that only eight copies of these minutes, which were originally labelled “SECRET”, were made. One of the materials discussed at the meeting was “49”. What was this material, which was considered so secret that a code name had to be used for it even in a SECRET, highly-controlled, document?
The material was plutonium-239 (Pu-239), an isotope with an interesting background. Glenn Seaborg and his colleagues at UCLA Berkeley are generally credited with “discovering” plutonium in 1940 and it is usually regarded as a “man-made” element. However, as Seaborg later reported in a 1951 paper, it has existed in nature for as long as the planet itself. Uranium 238 (U-238) occasionally undergoes spontaneous fission, which releases a number of neutrons. These neutrons can be absorbed by adjacent U-238 atoms in an ore body to form U-239 which decays to short-lived (half-life 2.4 days) Np-239 and then to long-lived (half-life 24,100 years) Pu-239. The concentration in ore bodies is, admittedly, very low with only a few micrograms of plutonium in every tonne of uranium.
As soon as sufficient quantities of Pu-239 became available from the first reactors so its nuclear properties could be measured, it became clear that Pu-239 would be an important material for nuclear weapons and the shroud of secrecy descended on it. Work was started in many laboratories, including Chalk River, on the chemical properties of the element. A group led by Bernie G. Harvey set to work with a 5 mg sample of the material. Harvey had been a member of the Tube Alloys team from the UK and remained in Canada following the return to Britian of many of the rest of the Tube Alloys team.
In 1947 the Chalk River group listed as “B.G Harvey, H.G. Heal, A.G. Maddox and (Miss) E.L. Rowley” published the first scientific paper on plutonium. It was titled “Chemistry of Plutonium” and appeared in the Journal of the Chemical Society.
Seaborg and his group at Berkeley were sufficiently impressed by the Chalk River work that within a short time Bernie Harvey became a staff member in the Seaborg group. Among his many distinguished accomplishments there, he is credited as being the co-discoverer in 1955 of the new element mendelevium (Z=105). He also played a role in the discovery of einsteinium (Z=99) and fermium (Z=100).
While at the CNHM we do not have any samples of isolated plutonium that we can offer visitors to view, we do have a ~2 kg sample of ore from Blind River that is used as the base of a retirement gift for Les Haywood. Back-of-the-envelope calculations tell us that there should be of the order of one nanogram of plutonium in this sample based on the concentrations reported by Seaborg. Spotting those sparce atoms is a task we leave to good imaginations.
