Mo can be obtained by the neutron activation (n,γ reaction) of Mo in a high-neutron-flux reactor. However, the most frequently used method is through fission of uranium-235 in a nuclear reactor. While most reactors currently engaged in Mo production use highly enriched uranium-235 targets, proliferation concerns have prompted some producers to transition to low-enriched uranium targets. The target is irradiated with neutrons to form Mo as a fission product (with 6.1% yield). Molybdenum-99 is then separated from unreacted uranium and other fission products in a hot cell.