For over thirty years, from 1979 to 2013, the McLennan building hosted ISOTRACE, a world centre for Accelerated Mass Spectrometry (AMS) research.
The closing of the Linac laboratory in the late 1970s left behind it a great deal of specialized laboratory space and a growing team of particle physicists. Physics Professor Ted Litherland, had recently been integral to experiments at the University of Rochester that showed that Carbon-14 and other isotopes could be counted using a tandem accelerator. With support from both geology and physics, a case was made to establish an AMS laboratory in the former Linac target room.
Carbon-14 is produced when cosmic rays interact with the CO₂ in the upper atmosphere. This radioisotope is incorporated into living tissue. When an organism dies, the C-14 decays into N-14, producing a method of dating carboniferous material up to about 50,000 years. Since its discovery in the late 1940s, C-14 dating had been accomplished by counting decay events. However, a series of accelerator experiments over the 1960s and 1970s hinted that C-14 and various other isotopes could be measured by sending sample material through an accelerator, separating the nuclei by mass, and counting the targeted particles.
By the 1970s, a new generation of sputter ion sources made it possible to test this hypothesis. The critical experiments took place over several years at the University of Rochester, where physicist Ken Purser (1929-2018) supplied ion sources for the Rochester MP tandem accelerator. In May of 1977, Ted Litherland and a group of collaborators first detected a C-14 signal.
The subsequent effort to establish an AMS laboratory at Physics was supported by the influential geophysicist David Strangway (1934 – 2016) who saw the value in measuring C-14 and other radioisotopes for geological research. The ISOTRACE facility was founded in 1979. Three years later, the tandem accelerator was completed and operational. The facility operated until 2013. It was superseded by the current André E. Lalonde National Facility in Accelerator Mass Spectrometry at the University of Ottawa.
Model of an EN Tandem Accelerator (c. 1960s)
A version of the accelerator depicted by this model was used by the IsoTrace laboratory.
This model represents the first tandem model built by High Voltage Engineering (HVEC), in Massachusetts. The first tandem accelerator of this kind was installed at Atomic Energy of Canada in 1959, where it was used by Dr. Ted Litherland. A later model was the basis for the Department of Physics IsoTrace AMS.
The model was donated to the University of Toronto by Susan Purser, daughter of physicist and engineer Dr. Kenneth H. Purser. Ken Purser was instrumental in improving the AMS voltage supply and ion source. These developments made it possible to use the technology for radioisotope dating.
These tiny sample slugs were the basis for radiocarbon dating at the IsoTrace AMS.
These carbon samples were used in the radiocarbon dating process developed by the IsoTrace laboratory. They consist of a cylindrical aluminum slug with a small amount of sample carbon pressed onto one face. The slug is placed in a cesium sputter source that releases the carbon into the accelerator.
This sample preparation method was developed by Dr. Rolf P. Beukens at the Chalk River Nuclear Laboratory, as well as on the 1 Mv JN Van Der Graaff accelerator that was used at the University of Toronto Department of Physics before the opening of the IsoTrace Laboratory in 1982.
These are probably early samples; at one point in the lab’s operation, a handling error prompted the laboratory to begin laser engraving sample numbers on the aluminum slugs. These examples are lack this engraving.
Maple Test Blank For IsoTrace Upgrade (c. 2000)
This wooden test piece was created as part of a significant upgrade to the IsoTrace tandem accelerator.
After around twenty years of almost continuous operation, the glass accelerator tube on the tandem accelerator had developed microscopic cracks and needed to be replaced. A major upgrade was undertaken, the first phase of which was completed in March of 2000.
As part of this process, researchers and technicians at the University of Toronto undertook to solve a misalignment in the accelerator tube caused by around 150 glue joints. The solution involved a new insulator to support the tube assembly at its centre. This required a modification to the high voltage terminal cover plate. This wooden test piece was produced during the process of machining a stainless steel metal opening that was welded into the terminal cover plate.