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Development of nanofibrous target materials for short-lived isotope production Wong, John


For over a decade, refractory metals and carbide powder materials have been used to produce radioactive ion beams (RIB) using the isotope separation online method at the ISAC facility at TRIUMF. A continuous 500 MeV proton beam generated from the world’s largest cyclotron is used to bombard the target materials to produce exotic isotopes. Particularly, short-lived isotopes are of high degree of interest in many disciplines including medicine, but only limited quantities are available due to the nuclear decay during the time associated with the diffusion and effusion of the species to migrate from the target materials to the ion source. The target materials are required to operate at high temperature to promote the release of the species; therefore, sintering of the grains is promoted, which results in lengthening of the diffusion paths for the isotopes causing the reduction of RIB yields. A possible way to improve the intensities of RIBs is by incorporating nanoparticle materials into nanofibres to increase the release efficiencies. In this study, nanometric SiC fibre target materials are fabricated by electrospinning. Upon a high-temperature heat treatment process, the organic carrier converts into a carbon fibre backbone that immobilizes the SiC target material with controlled nanometric grain size and reduced sintering dynamics. The weight composition of the final product is determined to be 60% SiC and 40% carbon nanofibre. The nanofibres were pressed into discs to achieve a combination of highly dense (1.1-1.2 g/cm³) and porous (56-54% total porosity) target materials, preserving the fibre morphology. The nano-SiC fibrous target material will be tested in September 2018 to evaluate the RIB yields explicitly for the short-lived isotopes at several milliseconds such as ²²Al (91.1 ms), ²⁰Mg (90.8 ms), ²¹Mg (122 ms), and ²⁰Na (447.9 ms).

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