Abstract
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Objectives Our previous efforts on production of 89Zr with a commercially available 18F target (Bruce Tech. TS-1650) showed feasibility of the approach but only after use of a back-pressure regulator to bleed gases from the target. The objective of the present study was to develop a solution target with improved heat exchange capacity for cost-effective routine production of radiometals using a medium energy cyclotron.
Methods In the present study we designed a prototype target with a water-cooled tantalum insert (1.6 mL volume) for the target solution and dual foils (0.2 mm Al and 20-40 μm Havar) separated by a helium cooling region. The beam energy was effectively degraded to ~14 MeV. The newly designed target was operated as a closed system (no venting) and tested for the production of 89Zr using 1.7-2.75 M Y(NO3)3 solutions in 1 N HNO3 and 63Zn using 1.7 M 63Cu(NO3)2 in 0.1 N HNO3.
Results The target was initially tested for production of 89Zr with 1.7 M Y(NO3)3 solution and an initial overpressure of 30 psi helium. Target pressure stabilized at <90 psi for a beam current of 20 μA over a 3 h irradiation interval. Production yield of 89Zr was 236 MBq. When Y(NO3)3 concentration was increased to 2.75M, target pressure increased slowly (1.0-1.7 psi/min) over the first 30 min at beam currents of 20-40 μA. Production yields of 89Zr were 48-76 MBq for 30 min irradiations. For 63Zn production using beam current of 20 μA, target pressure became stable at 113 psi over the interval 35-75 min. Isolated yield of 63Zn was 1.47 GBq uncorrected.
Conclusions The improved thermal transfer properties of the novel target enable it to be operated as a closed system. Target pressure can be stabilized depending on solution composition and beam current. The novel target design can be applied for production of a variety of radiometal nuclides, including 89Zr, 64Cu, 68Ga, and 63Zn.
Research Support The work was supported by DOE (DE-SC00008947)