Radioactive decay

Imagine you have a big box of colored candies. Each candy is made up of tiny particles called atoms. Some of these atoms are very special because they are not very stable, which means they don't stay the same for very long - they start falling apart after a certain amount of time. This is called "radioactive decay".

Just like how you can break a candy into smaller pieces, these unstable atoms break down into smaller pieces too. When this happens, they shoot out little particles called "radiation" - kind of like tiny invisible bullets.

This radiation can be dangerous if you get too close to it, but scientists can use it for all sorts of things too. Some people use it to treat cancer, while others use it to power machines like nuclear reactors.

Basically, radioactive decay is when certain types of atoms break down and shoot out a specific type of particle that can be dangerous, but also useful in certain situations.