Why can't we use electron-positron annihilation as an energy source? Unlike antiprotons, positrons sometimes pop out of beta decay and positron-producing isotopes with short half lives are routinely produced in cyclotrons around the world for hospital PET-scanners. Positrons and electrons both have a charge, so magnetic confinement should be possible. And electrons are 1/1836th of the mass of a proton, so compared to the equivalent mass of protons/antiprotons, we'd need about 1836 times as many positrons/electrons. Since positrons come out of beta decay, this shouldn't be that difficult. Reactors that rely on matter-antimatter annihilation are popular in science fiction. How feasible would it be to use these isotopes to produce positrons for positron-electron annihilation and energy production?