Carbon foils are being used at particle acclerators everywhere as extractor or stripper foils - as such, these are a very important part of many of the subatomic processes that take place at TRIUMF. When these films became unavailable from a foreign supplier, Dr. Stefan Zeisler and Vinder Jaggi had to get creative. They came up with a way to make these foils in-house, using a well-known process called Carbon Arc Deposition. The process involves the sublimation of a material, in this case amorphous carbon, onto glass slides, such that a film can be deposited and removed easily and afterwards used to extract beams. In their attempt to find an adequate film for MDS Nordion's cyclotron, these two researchers and a colleague from Texas (Dr. Nalin Kumar) discovered the benefits of layering foils in a sandwich-like manner with the diamond-like carbon in the center of two amorphous carbon layers.
Using this new technique, the types of film that can be constructed are quite variable - not only can the scientist using the film change the number and order of the layers, he/she can also change the relative thickness of the layers according to the desired performance of the composite film. Typically, thin foils can be made to measure 5ug/cm2 to 100ug/cm2; however, the new foils made at TRIUMF are at an astounding weight of 200ug/cm2 to 300ug/cm2. Other benefits of using diamond-like carbon include extreme hardness, optical transparency, chemical inertness, and high-wear resistance, all of which enable longer foil lifetime. Since the film would be more durable, replacement time would diminish, allowing decreased radiation exposure to maintence personnel and lower foil replacement costs. Having these higher-quality foils also allwos the researchers to use higher beam densities in their experiments while causing less graphitization of the carbon in the foil.
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Official patent applications have been filed for this technology. For the future, these two researchers see applications in nuclear medicine, PET centers, the radiopharmaceutical industry or even a possible spin-off venture, in addition to providing TRIUMF's cyclotron users with high-quality, durable foils. They were excited about the possibilites with laser ablation techniques specifically, and hope that TRIUMF's recent laser purchase will continue to streamline their manufacturing process and inspire innovative foil production methods.