5. Radioactive decay

Gamma decay

Cartoon showing gamma decay.

Cartoon showing gamma decay.During gamma decay the nucleus emits radiation without actually changing its composition: We start with a nucleus with 12 protons and 12 neutrons, and we end up with a nucleus with 12 protons and 12 neutrons… but somehow radiation gets released along the way!The nucleus is made out of a glued-together arrangement of protons and neutrons, but there are multiple possible ways that these protons and neutrons can be arranged. Some of these arrangements have a lower total energy, and so a nucleus in which the protons are initially close together may shift to the lower energy configuration after some time.Recall that the electrons orbiting the nucleus have energy levels, and that each time an electron moves from a high energy level to a low energy level it emits a photon.

The same thing happens in the nucleus: when it rearranges into a lower energy state, it shoots out a high-energy photon known as a gamma ray.Gamma rays are very high energy and are one of the most dangerous sources of radiation because photons can pass through most common shielding materials and cause DNA damage in living tissues. But gamma radiation also has practical uses; for example, the element technetium emits relatively low-energy gamma decays that can be detected using a specialized scanner, and so it has found use as a tracer element for imaging the inside of patients’ bodies.

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