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Modern Physics

Releasing Particles

Radioactivity occurs when an atomic nucleus breaks down into smaller particles. There are three types of nuclear radiation: alpha, beta, and gamma. 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. Alpha and Beta are particles, but Gamma is a wave.

Half of a Life

When a radioactive nucleus changes, the remaining nucleus (and atom) is not the same as it was. It changes its identity. 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. Let's say you have 100g of uranium (don't try this at home, it’s radioactive). When 50g remain (and 50g have become something different), the amount of time that has passed is the half-life. Every element has its own unique half-life. The half-life of uranium-235 is 713,000,000 years. The half-life of uranium-238 is 4,500,000,000 years. 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!

There is even a radioactive isotope of carbon, carbon-14. Normal carbon is carbon-12. C-14 has two extra neutrons and a half-life of 5730 years. Scientists use C-14 in a process called carbon dating. This process is not when two carbon atoms go out to the mall one night. Carbon dating is when scientists try to measure the age of very old substances. There are very small amounts of C-14 in the atmosphere. Every living thing has some C-14 in it. Scientists measure the amount of C-14 in the things they dig up to estimate how old they are. They rely on the half-life of 5730 years to date the object.

A Danger to DNA

Radioactivity is generally not good for living organisms. There are times that radiation passes right through organisms with no effect, but there are other times that it hits DNA or affects replicating cells. Bad things can happen when DNA is exposed to radiation. One result of moderate levels of radioactive particles can be cancer. Cells reproduce in ways that are not normal. High doses of radioactivity can kill a human within 24 hours. Medicine, however, has learned how to use radioactivity to stop cancers. Since they know that excess levels of radioactivity can kills cells, doctors target areas of cancer with radioactivity to stop the cancer cells from dividing.

Next Stop On Physics4Kids Tour
Next page on modern physics.
- Overview
- Nuclear Physics
- Quantum Physics
> Radioactivity
- Fission
- Fusion
- Reactors


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NASA Harnesses Half-Life (NASA-eClips Video)
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Useful Reference Materials
Wikipedia (Radioactive Decay):
Encyclopædia Britannica:

- Physics4Kids: Fission
- Chem4Kids: Atoms
- Chem4Kids: Atomic Structure
- Chem4Kids: Isotopes
- Geography4Kids: Energy Resources
- Geography4Kids: Solar Radiation
- Cosmos4Kids: The Sun
- Cosmos4Kids: Stars

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