Half-life

Half-life is like when you have a big pile of cookies and you keep taking half of the cookies away every few minutes. If you start with 10 cookies and take away 5 after 5 minutes, you'll have 5 cookies left. Then, after another 5 minutes, you take away half of those 5 cookies (which is 2.5 cookies, but we'll just say 2), so you'll be left with only 2 or 3 cookies. This will keep going on until there is only one cookie left, and then half of that cookie will still be left, but you can't really divide a cookie into half like that.

In Science, half-life is when a radioactive atom loses half of its particles and changes into a new atom. This happens because the radioactive atom is unstable and wants to become more stable. So every time half of the particles leave, the atom becomes more stable, but it's still a little bit unstable.

For example, if you have 1000 radioactive atoms and the half-life of that substance is 1 hour, after 1 hour, only 500 radioactive atoms will be left. Then, after another hour, half of those 500 radioactive atoms will be gone (250 left). This will keep going on until there are only a few radioactive atoms left.

Scientists use half-life to figure out how long it takes for a substance to decay and become non-radioactive. This is important because some radioactive substances can harm living things, so it's important to know how long they will stay radioactive.