A Table-Top Positron Source That Needs No Radioactive Isotopes

For most university labs, doing positron science still means relying on a sodium-22 capsule—a radioactive source that decays continuously, weakens with time, and can never be switched off. This paper describes a different approach: a compact positron beamline built around a 6 MeV medical linac. Electrons strike a tungsten target, producing bremsstrahlung photons that pass through a high-pressure xenon gas cell and turn into electron-positron pairs. A simple magnetic chicane separates the fast positrons, a thin tungsten foil slows them to a few electron-volts, and electrostatic lenses guide them to the sample. The expected slow-positron flux is around 1.8 × 10⁵ per second—directly comparable to a typical sodium-22 setup, but without the radioactive inventory, without the decaying output, and with the ability to turn the beam off at the flick of a switch. The whole system fits on an optical table and uses no cryogens.