Let's say you have 100g of uranium (don't try this at home, it’s radioactive). The half-life of uranium-238 is 4,500,000,000 years.When 50g remain (and 50g have become something different), the amount of time that has passed is the half-life. That is a long time to wait for radioactive atoms to change, and many of the things that the original atoms change into are ALSO radioactive and dangerous!
Radioactivity occurs when an atomic nucleus breaks down into smaller particles.
There are three types of nuclear radiation: alpha, beta, and gamma.
There is even a radioactive isotope of carbon, carbon-14. C-14 has two extra neutrons and a half-life of 5730 years.
Scientists use C-14 in a process called carbon dating.
Alpha particles are positively charged, beta particles are negatively charged, and gamma particles have no charge.
The radiations also have increasing levels of energy, first Alpha, then Beta, and finally Gamma, which is the most energetic of all these. When a radioactive nucleus changes, the remaining nucleus (and atom) is not the same as it was. The term half-life describes the time it takes for half of the atoms in a sample to change, and half to remain the same.