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How is radon gas connected to radioactive decay in rocks and minerals?

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radioactivity Figure 1: Radioactive decay of beryllium-7 to lithium-7 by electron capture (EC; see text).

Radon gas is a direct product of the radioactive decay of radium, which itself occurs naturally as a decay product of uranium present in various types of rocks and minerals, such as granite.12

Because radium is distributed within these geological formations, the radioactive decay process continuously generates radon gas. As a heavy noble gas, radon is capable of diffusing through the pores of soil and rock. From these underground sources, the gas can seep into the atmosphere or migrate into buildings, particularly through basements or water supplies derived from wells.12

The presence of radon is significant in radioactive surveys used to detect ore or rock bodies, as it serves as a natural indicator of the underlying radioactive mineral deposits. Once formed, radon continues to decay into radioactive "daughters," such as isotopes of polonium, bismuth, and lead.312