Gamma Rays

Gamma rays ($\gamma$-rays) were discovered by P. Villard in 1900. Unlike the other bands of the spectrum, which mostly originate from electron transitions in atoms or from accelerating charges in circuits, gamma rays are emitted directly from the nuclei of certain radioactive elements, such as uranium and radium, as those nuclei undergo transitions between different nuclear energy levels.

Gamma rays are the highest-energy EM waves in the entire spectrum, with photon energies spanning roughly the keV to GeV range. They are highly penetrating -- more so even than X-rays -- yet, somewhat counter-intuitively, they have only a comparatively small ionising power per interaction (though the harm they can do to living tissue remains severe, since even a small ionising probability per interaction adds up over the very large number of interactions a highly penetrating beam makes as it passes through matter); like ultraviolet and X-rays, they are capable of killing living cells. Applications exploit exactly this cell-killing, high-penetration combination: gamma rays are used as an insecticide-disinfection treatment for stored wheat and flour, for food preservation more generally, in radiotherapy for the treatment of cancer and tumours, and to induce nuclear reactions in physics and industry. Taken together with ultraviolet and X-rays, gamma rays complete the group known as ionizing radiations -- all three carry enough energy to strip electrons from the atoms and molecules along their path, and this shared ionizing …