Section 1 of 6Interaction with electrons
1Absorption
- Absorption When an atom absorbs EM radiation of the right energy, an electron can move to a higher energy level further from the nucleus.
2Excited atom
- Excited atom The atom is now in an excited state. This is unstable.
3Emission
- Emission The electron falls back to a lower level and the atom emits EM radiation, with energy equal to the difference between the levels (HT only).
4Ionisation
- Ionisation If the radiation has enough energy, an electron is removed completely and the atom becomes a positive ion.
Section 2 of 6Changes in atoms and the radiation involved
| Event | Part of atom | Radiation involved |
|---|---|---|
| Electron moves between energy levels | Electron shells | Visible light, ultraviolet, infrared |
| Inner electron changes level | Inner electron shells | X-rays (high energy) |
| Nucleus becomes more stable after decay | Nucleus | Gamma rays |
| Electrons oscillating in a conductor | Free electrons in a wire | Radio waves |
Section 3 of 6Ionising radiation
Which waves
- Which waves Ultraviolet, X-rays and gamma rays are ionising: each photon has enough energy to remove electrons from atoms.
Damage to cells
- Damage to cells Ionisation can damage DNA in cells.
- This may kill cells or cause mutations that lead to cancer.
Non-ionising waves
- Non-ionising waves Radio, microwaves, infrared and visible light do not usually ionise, and mainly cause heating.
Section 4 of 6Hazards and protection
Risk from EM radiation
Ultraviolet
- Ultraviolet Causes sunburn, premature skin ageing, eye damage and skin cancer. Use sunscreen and sunglasses.
X-rays
- X-rays Can cause cell damage and cancer.
- Radiographers stand behind lead screens and patients get the smallest dose needed.
Gamma rays
- Gamma rays Very penetrating and can cause cancer. Thick lead or concrete is used for shielding.
Dose and time
- Dose and time The risk depends on the dose, which increases with exposure time and the energy of the radiation.
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Ionisation | The process of removing electrons from an atom to make an ion. |
| Excited state | A state of an atom in which an electron has moved to a higher energy level. |
| Gamma ray | High-energy EM radiation emitted from a nucleus. |
| Ionising radiation | Radiation with enough energy to remove electrons from atoms. |
| Dose | The amount of radiation absorbed by a person or material. |
Section 6 of 6Exam technique
1
Saying that radio waves are ionising. They have too little energy per photon.
2
Stating that gamma rays come from electron shells; they come from the nucleus.
3
Believing that radiation makes a person 'radioactive'. Exposure to X-rays does not make you radioactive.
4
Mixing up the direction of electron movement: absorption lifts electrons up, emission happens as they fall down.