5. Radioactive decay

What are the types of nuclear reaction?

Alpha Decay

Cartoon showing alpha decay.

Cartoon showing alpha decay.During alpha decay, a nucleus actually breaks up into two chunks: a pair of protons bound to a pair of neutrons (a collection of four particles which is essentially a helium nucleus, and is called an alpha particle), and another piece constituting the original nucleus minus this chunk. So we can actually write down a chemical reaction equation for alpha decay:

Ra → Rn + He^{2+}

start superscript, 2, plus, end superscriptThe radium nucleus (Ra, atomic number 88) breaks up into the helium nucleus (He^{2+}start superscript, 2, plus, end superscript, the little chunk) and a daughter nucleus that corresponds to the element radon (Rn, atomic number 86). The medical risks associated with radiation usually involve the fast speeds at which the products of nuclear reactions move.Think of the alpha particle released by this reaction as a tiny bullet, which can puncture soft tissues like the lining of the stomach and lungs. Fortunately, alpha decay tends to release large, slow-moving decay products, and so it’s easy to shield against this type of radiation.

The reaction shown above illustrates another, indirect method by which alpha decay can pose a hazard. Radium, the element on the left hand side of the reaction arrow, can be found deep underground as a solid rock mixed in with granite. However, when it undergoes alpha decay it turns into radon, which naturally prefers to be a gas. The radon then seeps out of the ground and into the basements of people’s homes, where it can enter their lungs and then decay again, releasing more alpha particles (or other types of radiation) directly into the unprotected tissues. This method of radon exposure represents a major lung cancer risk factor in many parts of the world.

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