Targetry for the in-beam activation of tracer particles for positron emission particle tracking

Abstract

Positron emission particle tracking measures the trajectory of a single radioactively labelled tracer particle by coincident detection of emitted annihilation photons. The technique enables the non-invasive study of dense opaque flows, with the tracer acting as a small neutrally buoyant flow-follower. The University of Cape Town has established a PEPT facility at iThemba LABS, utilising tracer particles produced through radiochemical methods, and measured using adapted positron tomographs. An activation approach producing the positron emitter 18F inside glass target spheres of diameter between 5.0 and 10 mm using accelerated beams of alpha-particles has been explored. The reaction 16O(O, x)18F is used, exploiting the high concentration of natural oxygen and the correspondingly high cross-sections for 18F formation. A standard target holder for the batch production of radionuclides at iThemba LABS was modified, reducing the entrance window thickness, allowing ingress of circulating cooling water, and adapted for a primary tparticle beam of 100 MeV energy delivered by the separated sector cyclotron (SSC) of iThemba LABS. Two-hour bombardment at nominal beam current 0.8 eµA produced activities up to ~ 110 MBq (3 mCi), with over 95% of the activity being 18F.