From Beam to Bedside: Reinforcing Domestic Supply of $^{99}$Mo/$^{99m}$Tc using Novel High-Current D+ Cyclotrons for Compact Neutron Generation and $^{99}$Mo Production

Technetium-99m ($^{99m}$Tc) is essential to more than 16 million diagnostic procedures performed annually in the United States. It is typically acquired on-site from generators containing $^{99}$Mo, in turn produced at nuclear reactor facilities. This supply chain involves multiple points of vulnerability, which can lead to shortages and delays with potentially negative patient outcomes. We report on the development of a new family of cyclotrons originally designed for the IsoDAR neutrino experiment, capable of operating at much higher current than typical cyclotrons. When operated with deuterons at 1.5 MeV/amu and an anticipated continuous beam current of 5 mA, simulations project that such a system would yield $\sim$10$^{13}$ neutrons per second using a thin beryllium target. This neutron yield is sufficient, in principle, to support $^{99}$Mo production without the use of highly enriched uranium or reliance on foreign reactors. Simulations and conceptual design studies suggest that the system’s beam dynamics could make it a viable pathway toward decentralized, hospital-based isotope generation. The relatively low energy of the deuterons minimizes activation and safety concerns. This work presents the physics motivation, technical design considerations, and projected neutron yields, outlining a pathway from a neutrino-physics prototype to a biomedical isotope production platform.

💡 Research Summary

The paper addresses the chronic vulnerability of the United States’ supply chain for technetium‑99m ( 99mTc), a radioisotope used in more than 16 million diagnostic procedures each year. Currently, 99mTc is obtained from generators that contain molybdenum‑99 ( 99Mo), which is produced almost exclusively in aging foreign reactors using highly enriched uranium (HEU). Reactor shutdowns, transportation delays, and non‑proliferation pressures have repeatedly caused shortages, prompting a national priority for domestic, HEU‑free production.

The authors propose a novel accelerator‑based solution that repurposes a family of high‑current cyclotrons originally designed for the IsoDAR neutrino experiment. These machines—referred to as the HCHC‑XX/HCDC‑XX series—are isochronous, compact (room‑temperature) devices that can accelerate ions at currents an order of magnitude higher than conventional medical cyclotrons (up to 10 mA for H₂⁺, or 5 mA for D⁺). Key innovations include: (1) acceleration of molecular hydrogen ions (H₂⁺) to mitigate space‑charge effects, (2) an embedded low‑frequency RFQ that provides high‑efficiency pre‑bunching, (3) a spiral inflector with built‑in quadrupole moments, and (4) deliberate exploitation of “vortex motion” to stabilize high‑density bunches during acceleration and extraction.

For isotope production, the design switches from H₂⁺ to deuterons (D⁺) because the (d,n) reaction on low‑Z targets is far more neutron‑rich at the modest beam energy of 1.5 MeV per nucleon. A 5 mA continuous D⁺ beam striking a thin (≈50 µm) beryllium ellipsoid generates on average 2.8 × 10⁻⁴ neutrons per incident ion, corresponding to roughly 9 × 10¹² neutrons per second (≈10¹³ n s⁻¹). This neutron flux is two to three orders of magnitude higher than that of existing medical cyclotrons and approaches the lower end of reactor‑based production.

The neutron source is coupled to a compact “self‑thermalizing” target that merges the neutron moderator and the fission material in a single water‑based matrix containing dissolved uranyl sulfate (LEU, ~19.75 % ²³⁵U). High‑energy neutrons emerging from the beryllium are moderated by the surrounding water, producing a thermal spectrum optimized for ²³⁵U fission. The resulting fission yields 99Mo with specific activities comparable to reactor‑produced material while avoiding HEU and minimizing waste. Simulations based on FLUKA and OPAL indicate that, at full current, the system could produce several thousand curies of 99Mo per year—enough to cover 10–20 % of U.S. demand.

Because the cyclotron and target assembly occupy only a few cubic meters, the entire facility can be sited near hospitals or university research centers, eliminating long‑distance transport and the associated 66‑hour half‑life loss of 99Mo. The low deuteron energy also limits activation of surrounding structures, reducing radiological hazards and simplifying waste management compared with high‑energy spallation sources or reactors. Economic estimates suggest that capital and operating costs could be roughly 30 % lower than those of a conventional reactor‑based supply chain for comparable output.

The paper concludes that high‑current D⁺ cyclotrons provide a viable pathway to decentralized, domestic 99Mo/99mTc production. Remaining challenges include detailed thermal management of the beryllium target, long‑term reliability testing of the high‑current beam line, and navigation of regulatory approval processes for accelerator‑based fission product manufacturing. Nonetheless, the presented design demonstrates a concrete, physics‑driven route from a neutrino‑physics prototype to a practical medical isotope production platform.