Radioactivity and gamma rays
Unstable nuclei and very penetrating rays
1. Economic importance of the first transition series
2. Rays from outside
Doctors can treat a tumour deep inside the body with rays sent from outside. What kind of ray can reach that far?
Pick the right answer
Predict: what must such a ray be able to do?
- A. Pass through skin and flesh
- B. Be visible, like ordinary light
- C. Be attracted by a magnet
الشرح
To reach a tumour deep inside the body, the ray must pass through skin and flesh: it needs high penetrating power, as gamma rays have.
3. Unstable nuclei
Remember: isotopes of an element differ in their numbers of neutrons.
Radioactive isotope
An isotope with an unstable nucleus that breaks down by itself and gives out radiation.
| Isotope | Nucleus |
|---|---|
| Carbon-12 | stable |
| Carbon-14 | unstable: radioactive |
4. Gamma rays
Remember: gamma rays sit at the high-energy end of the electromagnetic spectrum.
Many radioactive nuclei give out gamma rays. They are electromagnetic rays with very high energy and high penetrating power.
5. Exposed is not radioactive
- Gamma source (holds the radioactive isotope) → Food or tools (gamma rays pass through)
- Food or tools → Not radioactive (rays are gone)
Contrast: a dental X-ray passes through your teeth. Your teeth do not start giving out rays.
6. Check it
Pick the right answer
Sealed packs of medical gloves are passed near a gamma source to kill germs. Afterwards, the gloves are:
- A. Free of germs, and not radioactive
- B. Radioactive for some time
- C. Holding gamma rays trapped inside the pack
الشرح
The gamma rays pass through the sealed pack and kill the germs. The gloves take in no radioactive isotope and the rays are not stored, so the gloves give out no radiation afterwards.
True or false?
Gamma rays have high penetrating power.
الشرح
Gamma rays have high penetrating power: they pass through paper, the body and thin metal. That is why they can kill germs inside a sealed pack.
Fill in the blanks
An isotope with an unstable nucleus that gives out radiation is called a _____ isotope.
الشرح
It is a radioactive isotope.
7. Summary
- A radioactive isotope has an unstable nucleus that gives out radiation.
- Gamma rays are high-energy electromagnetic rays with high penetrating power.
- Gamma rays used to treat food or tools do not make them radioactive.
Back to the hook: gamma rays can reach a tumour because of their high penetrating power.
Can you explain why food treated with gamma rays is safe to eat?
Reveal
Gamma rays used to treat food pass through it and are gone. The food does not become radioactive: only the source contains the radioactive isotope.