The Value and Cost of Fusion Neutrons
Deuterium-tritium fusion reactions produce high-energy neutrons that can transmute materials into valuable isotopes. Over the next ten years, the cost of fusion neutrons is projected to decrease by roughly seven orders of magnitude. Most ($\sim$5 orders of magnitude) is technological overhang driven by the low availability of current experiments; the remaining $\sim$2 orders of magnitude require higher plasma gain and lower capital intensity. We introduce the levelized cost of a neutron (LCON), an economic metric analogous to the levelized cost of energy that gives the minimum neutron value for economic breakeven of a fusion system. LCON depends on plasma gain, capital intensity, availability, and neutron flux, and is offset by revenue from co-produced electricity, precious metals, and radioisotopes. The revenue per neutron spans at least ten orders of magnitude, from electricity and gold ($\sim$\$$10^{-20}$/neutron) to actinium-225 ($\sim$\$$10^{-10}$/neutron), defining a `neutron ladder': a staged, revenue-positive development pathway from current fusion devices to terawatt-scale power plants.