Applied Radioisotopes

TRIUMF’s accelerator infrastructure and expertise provides for a unique and fertile ecosystem for the development of isotopes for new medical applications. Over the past 5 years, the Life Sciences division has been working to expand its portfolio of isotopes beyond the traditional repertoire of positron- and gamma-emitting imaging isotopes to include a number of alpha-, beta- and Auger-emitting isotopes that can be used in therapeutic applications. Examples of isotopes recently produced for further study include ²¹¹At, ^212,213Bi, ²²⁵Ac, ²¹²Pb and ²¹²Bi. Interests also include ²²⁷Th, ¹⁴⁹Tb, ¹¹⁹Sb, ¹⁰⁵Rh and ⁶⁷Ga. To obtain these isotopes, the Life Sciences program at TRIUMF continues to exploit production capabilities on legacy (BL1A, TR-13 and ISAC) as well as future (ARIEL proton and electron beamlines, IAMI) infrastructure. With ready access to a broad repertoire of isotopes, TRIUMF scientists, along with their collaborators, will enable the production of new radiopharmaceuticals for Targeted Radionuclide Therapy (TRT).

Virtually contamination-free radioactive ion beams can now be provided at ISAC from a new ion-guide laser ion source (IG-LIS) [1]. This IG-LIS allows for experiments on isotopes that for decades have been overwhelmed by contamination from surface-ionized isobars. TRILIS now routinely provides isotopes from 37 different elements. Laser ionization schemes for an additional 24 elements are ready for off-line testing. TRILIS also supports an in-source laser spectroscopy program that investigates fundamental properties of the rarest isotopes such as atomic energy levels and elemental ionization potentials have been determined for the first time [2] or improved significantly [3].

New aqueous fluorination techniques: ¹⁸F is a key isotope for the production of many radiopharmaceuticals. For decades, the addition of ¹⁸F to radiopharmaceutical precursors required harsh (high temperature, anhydrous) chemical conditions in order to provide adequate yields of the desired products. These conditions typically degrade more sensitive biomolecules, such as antibodies, peptides and proteins. Over the past 5 years, TRIUMF has worked collaboratively with scientists at the University of British Columbia and Simon Fraser University to develop two novel aqueous fluorination methods. Efforts with Dr. David Perrin (UBC, Chemistry) enabled the development of aqueous aryltrifuloroborate chemistry for rapid, 1-step incorporation of ¹⁸F onto peptides and other biomolecules; while those with Dr. Robert Britton have resulted in a novel method that uses a light-activated catalyst to place fluorine atoms on very specific locations of certain amino acids. These methods give radiopharmaceutical chemists new tools by which to produce radiopharmaceuticals that have been, until now, inaccessible or too difficult to produce.

Novel radiopharmaceuticals for imaging unique metabolic pathways in cancer: Amino acids play an important role in many biological processes, serving a key role in protein synthesis and as substrates for important intermediary metabolic processes and cell signaling pathways. This makes them prime candidates for templates for new medical imaging probes – substances that can be used to diagnose and track the development of diseases. To this end, TRIUMF has developed novel tracers toward two molecular systems: x_C- and LAT1. System x_C- helps to maintain homeostasis via antioxidant/free radical management at the cellular level, while the LAT1 transporter is an important component of protein synthesis in cells. TRIUMF has developed ¹⁸F-fluoroaminosuberic acid (¹⁸FASu) as a specific positron-emitting substrate of system x_C-; and via collaborative efforts with scientists at SFU, a series of leucine-like radiolabeled amino acids as substrates of LAT1. Studies are ongoing to establish the utility of both tracers in the detection, staging and treatment monitoring of a number of different cancers.  

bNMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface Hard drives use disks made of magnetic material to store information, and an electromagnet in the read/write head writes information to the disk by magnetizing small sections of the disk. Increasing the information on a hard drive requires shrinking the size of the magnetic sections and this means the near-surface regions are increasingly important. The prototypical antiferromagnet α-Fe₂O₃ has a first-order transition known as the Morin transition at 260 K, where the orientation of antiferromagnetic order with respect to the crystal lattice undergoes an abrupt change. In this work the static spin orientation and dynamic spin correlations within nanometers from the surface of a single crystal was studied via the nuclear spin polarization of implanted ⁸Li ions and detected via bNMR spectroscopy. As reported in Physical Review Letters (2016), the experiment found that the Morin transition temperature was independent of depth from 1 to 100 nm from the free (110) surface but the fluctuations of the electronic spins are faster near the crystal surface and decay into the bulk over a characteristic length of 11 nm.  The results suggest the magnetic order parameter undergoes a continuous gradient rather than a phase separation of bulk vs. surface magnetism. Whereas previous studies made use of nanoparticles to achieve sufficient near-surface volume fraction to extract a signal, bNMR spectroscopy allowed a depth-resolved characterisation of the magnetic order parameter into a macroscopic single crystal of α-Fe₂O₃, differentiating free-surface and finite-size effects on magnetic order.

bNMR reveals nanoscale surface details in topological insulators: Wolfgang Pauli said, “God made the bulk; surfaces were invented by the devil”, a recognition of the fact that theories and experimental measurements of near-surface properties are very difficult. Surfaces may be difficult to study, but it is where much interesting physics arise. Topological insulators (TI) are materials where the bulk is an insulator but whose surface contains conducting states, which means that electrons can only move along the surface of the material. Topologically protected states could act as a source of spin-polarized electrons with properties relevant to spintronics applications including quantum computing. As published in the Proceedings of the National Academy of Sciences (2015) researchers at CMMS used bNMR spectroscopy as a nano-scale depth-resolved probe of magnetism and conductivity within about 10 nm of the free surface of (Bi,Sb)2Te3. This depth-dependent study of electronic and magnetic properties of TI epitaxial layers using implanted, spbin-polarized ⁸Li⁺ ions reveals differences in the band structure between the near-surface and deeper into the bulk material.