In the early 1950s the future of civilian nuclear power looked very bright. There was significant concern, however, that the worldwide need for uranium would greatly outstrip the known supplies. A possible solution, suggested by W.B. Lewis, was to breed fissionable material by the so-called “spallation” process.
The concept was to use high-energy (greater than 500 MeV) protons to produce copious numbers of neutrons from interactions between the protons and targets such as lead or bismuth. (Lewis talked in terms of grams of neutrons per day.) It was projected that each high-energy proton hitting a target would produce 20-40 neutrons.
These neutrons could then be absorbed in thorium to produce uranium-233 or in uranium-238 to produce plutonium-239, both of which can be split (fissioned) like uranium-235.
Lewis discussed his ideas with both the British and the Americans but quickly discovered a block in the information from the USA, where physicists apparently were secretly looking at the spallation process themselves.
A large problem for Lewis was a lack of good theoretical or experimental information on the yield of neutrons per proton in the high energy range being considered. No accelerators of the required energies had yet been built.
Nature fortunately does supply high-energy protons, in the form of cosmic rays produced throughout the galaxies. Unfortunately for the experimenters, but fortunately for life on earth, the cosmic rays are strongly attenuated by earth’s atmosphere and only about 0.5% of the proton flux of interest reaches the earth’s surface. The atmospheric interactions also produce a huge background of muon particles which complicate experiments.
The solution was to move to higher altitudes, to reduce the atmospheric attenuation. A research facility existed in Echo Lake, Colorado, at 3260 m above sea level. The proton component of the cosmic rays at this altitude was 11 times greater than at Chalk River. The ratio of protons to the interfering muons was also much higher. Permission was granted by the USA to conduct experiments at the Echo Lake site and a portable trailer was constructed for this purpose.
Results at Echo Lake were obtained from a concentrated experimental run in December 1955. The trailer then returned to Deep River where more data was collected at the lower flux. This data, finally published in 1960, was the only experimentally-measured data available at that time. It was used by Lewis and his collaborators to push for the Intense Neutron Generator (ING) accelerator project at Chalk River in the mid-1960s.
Hugh Carmichael of CRNL, Canada’s prime developer of cosmic ray detectors, further expanded Canadian cosmic ray measurements as part of a world-wide network of monitoring stations that recorded the variations in the cosmic ray flux both in direction and time. He led a group that installed a total of 18 monitoring stations across the Canadian Arctic.
A large A-shaped building (dubbed by locals as Carmichael’s chapel), just to the rear of the Canadian Nuclear Heritage Museum, housed his main cosmic ray detection equipment. The measurements from this laboratory played an important role in warning personnel on manned space flights of the radiation bursts from large solar flares. The Deep River station was shut down shortly after Carmichael retired in 1970 and now houses the offices of a legal firm.
To learn more about Canada’s early nuclear history visit the Nuclear Heritage website at www.nuclearheritage.com
Cosmic ray trailer in Deep River prior to leaving for Echo Lake. Back Row, L-R: M. Hudson Jr., J. Steljes, M. Berkovich, G. Johnston, W. McAlpin. Front: J. Mullin, H. McCrady, D. Tennant.
