MYP Physics Radioactivity and Decay, Forms of Radiation, Uses and Dangers Notes

Why Do some Materials Give Out Radiation, And How Can Radiation Be Both Useful And Dangerous?

1. Radioactivity is a natural process in which an unstable nucleus changes into a more stable one by emitting radiation.
2. Although radiation can be harmful, it is also extremely useful in medicine, industry, and energy production.

Radioactivity Happens When Nuclei Are Unstable

1. Atoms consist of a small, dense nucleus (containing protons and neutrons) with electrons around it.
2. Some nuclei are unstable because the balance of forces in the nucleus does not produce a long-term stable arrangement.
3. When this happens, the nucleus undergoes radioactive decay.

Radioactive decay

1. A key feature of radioactive decay is that it is not affected by typical chemical or physical conditions (such as temperature or pressure).
2. Those conditions mainly affect electrons, not the nucleus.

The Random Nature of Radioactive Decay

1. It is impossible to predict when a single nucleus will decay.
2. Two identical nuclei can decay at very different times.
3. However, when many nuclei are observed together, clear patterns appear.
4. This randomness leads to the concept of half-life.

Background Radiation Is Always Present

1. Even without any "nuclear sources" nearby, you are exposed to radiation every day.
2. This is called background radiation, and most of it comes from natural sources.

1. Rocks and soil

1. Some rocks contain long-lived radioactive elements such as uranium and thorium.
2. Their decay products can also be radioactive.
3. Building materials made from these rocks can contribute to indoor background radiation.

2. Radon gas (radon-222)

1. Produced in the decay chain of uranium-238.
2. Radon is a noble gas, so it does not easily react and can seep out of rocks.
3. It can accumulate indoors if ventilation is poor.

3. Food and living things

1. Some foods contain potassium, and a small fraction of potassium atoms are radioactive potassium-40.
2. Foods with high potassium content can therefore have slightly higher natural radioactivity.

4. Cosmic rays

1. High-energy particles from the Sun and deep space strike the atmosphere, producing showers of particles.
2. Some reach the ground.

What Is Half-Life?

1. After one half-life, half of the original nuclei have decayed.
2. After two half-lives, only one quarter of the original nuclei remain undecayed.
3. Each radioactive isotope has its own characteristic half-life.

Alpha, Beta, And Gamma Radiation Behave Very Differently

1. Radioactive decay can produce three main types of nuclear radiation: alpha (α), beta (β), and gamma (γ).
2. All three (α, β, γ) are ionising, meaning they can damage cells by knocking electrons out of atoms and molecules.

1. Alpha Radiation: Very Ionising, Poor Penetration

1. Alpha radiation consists of particles made up of two protons and two neutrons.
2. Alpha particles carry a positive charge and have a relatively large mass.
3. Because of their large mass, alpha particles strongly ionize materials they pass through.
4. Alpha radiation has very low penetration and travels only a few centimetres in air.
5. A sheet of paper or the outer layer of human skin is sufficient to stop alpha radiation.