The ruins of the Chernobyl reactor are enclosed in a huge concrete structure built around it after the accident. Some rain penetrates the building in winter, and radioactivity from the building increases. What does this imply is happening inside?

Radioactivity is a phenomenon in which a few substances spontaneously release energy and subatomic particles. The nuclear instability of an atom causes radioactivity.

This might be because the neutrons emitted by the radioactive substance are absorbed by the water, especially oxygen. When an oxygen nucleus takes a neutron, it transforms into radioactive nitrogen, increasing the building's radioactivity.

The following is the reaction,

\({}^1n + {}^{16}O \to {}^1p + {}^{16}N\) (Activation reaction)

We also have a reaction for decay,

\({}^{16}N \to {}^{16}O + \beta + \gamma \)

Therefore,\({\rm{\beta }}\)and\({\rm{\gamma }}\)radiations can pose a significant threat and are quite dangerous, which is why these showers might pose a significant risk.

On the other side, Chernobyl utilised polonium to generate energy, and rain can induce additional radioactive decay, posing a serious threat.