Which of the following radon decay products contributes the largest dose of radiation?

Polonium-218 is known to be a significant contributor to the dose of radiation that individuals may receive from radon decay products. This is primarily because of its alpha-emitting nature and the way it interacts with human tissue. When radon gas is inhaled, polonium-218 and other short-lived decay products can attach to dust and other particles in the lungs. As it decays, polonium-218 emits alpha particles, which have a high potential for causing biological damage due to their ability to deposit energy over a very short distance.

The decay chain of radon-222 involves several steps that produce various decay products, including polonium-218. While radon-222 itself is a health risk because it is the progenitor of the decay series, polonium-218, being one of the first decay products, poses a more direct risk once inhaled due to its immediate presence in the respiratory tract.

Understanding the properties of the decay products, particularly polonium-218's capacity to inflict radiation damage, clarifies why this particular isotope is considered to contribute the largest dose of radiation within the context of radon exposure.