Abstract
This paper presents a design and working principle for a combined powder-in-gas target. The excellent surface-to-volume ratio of micrometer-sized powder particles injected into a forced carrier-gas-driven environment provides optimal beam power-induced heat relief. Finely dispersed powders can be controlled by a combined pump-driven inward-spiraling gas flow and a fan structure in the center. Known proton-induced nuclear reactions on isotopically enriched materials such as 68Zn and 100Mo were taken into account to be conceptually remodeled as a powder-in-gas target assembly, which was compared to thick target designs. The small irradiation chambers that were modeled in our studies for powdery ‘thick’ targets with a mass thickness (g/cm2) comparable to 68Zn and 100Mo resulted in the need to load 2.5 and 12.6 grams of the isotopically enriched target material, respectively, into a convective 7-bar pressured helium cooling circuit for irradiation, with ion currents and entrance energies of 0.8 (13 MeV) and 2 mA (20 MeV), respectively. Current densities of ~2 μA/mm2 (20 MeV), induces power loads of up to 4 kW/cm2. Moreover, the design work showed that this powder-in-gas target concept could potentially be applied to other radionuclide production routes that involve powdery starting materials. Although the modeling work showed good convective heat relief expectations for micrometer-sized powder, more detailed mathematical investigation on the powder-in-gas target restrictions, electrostatic behavior, and erosion effects during irradiation are required for developing a real prototype assembly.
Highlights
Across the world, hundreds of cyclotrons with beam energies of 13 MeV and higher are applied for radionuclide production [1,2,3]
The design work showed that this powder-in-gas target concept could potentially be applied to other radionuclide production routes that involve powdery starting materials
Particle size in the table indicates a certain accuracy range for the operation. Particles outside this range will be transferred to the Powder injection and recovery (PIR) unit
Summary
Hundreds of cyclotrons with beam energies of 13 MeV and higher are applied for radionuclide production [1,2,3]. The cyclotron-based radionuclide production of 68 Ga and 99m Tc has gained particular interest owing to the growing demand for 68 Ga, and the expected shortages of the most widely used radionuclide, 99m Tc, obtained from 99 Mo/99m Tc generators. The cyclotron-based production of 99m Tc is an emerging technology that serves as an alternative to reactor-produced 99 Mo. For the Netherlands (population 18 million), the total daily 99m Tc demand corresponds to 20 MeV proton irradiations of 12,000 μAh in 6-hour-run batches each day. For the Netherlands (population 18 million), the total daily 99m Tc demand corresponds to 20 MeV proton irradiations of 12,000 μAh in 6-hour-run batches each day This daily demand can be covered by one or two cyclotrons of 2 mA current. Growing demands for the radioisotope 68 Ga for positron emission tomography can be met by an improved design of the 68 Zn production target
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