The gamma ray photons and iron atoms are tuned to react with each other in something called the Mossbauer isotope. When an iron nucleus absorbs a photon, it becomes unstable and releases a small burst of energy that knocks an electron out of its proper orbit, which then bumps outer electrons astray. What follows is an Auger cascade, a kind of microscopically localized electron explosion, Gagnon explains. The electrons are shooting off, breaking things all over the place, and then the iron becomes attached to the DNA fragments. There's no way a cell can repair so much damage.
Healthy cells tear apart the transport molecule and the iron drifts safely off.
It's just an amazingly clever idea. But having said that, this is nothing to sneeze at. The elegance of the idea is impressive. In addition, he says, the radiation used in his original tests was so negligible that he could increase it by a factor of 1000 without any resulting discomfort to the patient. Mills says he's since sharpened his technique to use ultrasound or magnetic scanners to take aim at malignant growths, and then destroy them with gamma rays pixel by pixel on a computer screen.