Introduction to Using and Staying Safe Around Radiation

In our previous studies, we looked at what radioactivity is and how it decays. Now, we are going to explore how we actually use this incredible energy in real life—from treating cancer to powering whole cities. We will also look at why radiation can be dangerous and how scientists keep us safe. Don't worry if the physics of "splitting atoms" sounds like science fiction; we will break it down into simple, easy-to-follow steps!

Dangers of Radioactivity

Radiation can be dangerous because it is ionising. This means it can knock electrons off atoms in our cells, which can damage DNA, cause mutations, or even lead to cancer. To stay safe, we need to understand the difference between two key terms that students often mix up: irradiation and contamination.

1. Irradiation vs. Contamination

  • Irradiation: This happens when an object is exposed to radiation from an external source. It is like standing near a fire to get warm; you feel the heat, but you don't "catch" the fire. If you are irradiated, you do not become radioactive.
  • Contamination: This happens when radioactive atoms actually get onto or into an object (like getting radioactive dust on your skin or breathing it in). This is much more dangerous because the atoms stay with you and keep decaying. In this case, you do become radioactive.

2. Safety Precautions

To minimize the risks, scientists and medical staff use several methods:

  • Shielding: Using lead-lined aprons or thick concrete walls to block radiation.
  • Distance: Using long-handled tools (tongs) to keep sources far away from the body.
  • Time: Minimizing the time spent near a radioactive source.
  • Monitoring: Wearing photographic film badges. The film changes color based on how much radiation it has absorbed, warning the wearer if they have reached a dangerous limit.

Quick Tip: If an exam question asks how to reduce risk, always think: "Shielding, Distance, and Time!"

Physics-Only: Medical Uses of Radioactivity

Note: The following sections are for students taking the full Physics GCSE.

1. Radioactive Tracers

Tracers are used to look at internal organs without surgery. A patient swallows or is injected with a radioactive isotope. A gamma camera outside the body detects the radiation as it moves through the organs.

  • Why Gamma? Gamma radiation is used because it is highly penetrating and can pass out of the body to be detected. Alpha or Beta would be absorbed by the body and cause damage.
  • Half-life: The isotope must have a short half-life (usually a few hours) so that it decays quickly and doesn't stay radioactive inside the patient for long.

2. PET Scanners

PET (Positron Emission Tomography) scanners are used to produce 3D images of the body. They work using beta-plus (\(\beta^+\)) decay.

  1. A tracer that emits positrons is injected.
  2. When a positron meets an electron in the body, they annihilate each other.
  3. This produces gamma rays that travel in opposite directions.
  4. The scanner detects these rays to build a precise map of where the tracer is (usually where the most metabolic activity is, like a tumor).

3. Treating Tumours (Radiotherapy)

Radiation can be used to kill cancer cells:

  • External treatment: Beams of gamma rays are aimed at the tumor from different angles to kill the cancer while minimizing damage to healthy tissue.
  • Internal treatment: A radioactive implant (usually a beta emitter) is placed right next to or inside the tumor.

Physics-Only: Nuclear Fission

Nuclear fission is the splitting of a large, unstable nucleus into smaller "daughter" nuclei. This process releases a massive amount of energy, which we use in nuclear power stations.

The Process of Fission in Uranium-235

  1. A slow-moving neutron is absorbed by a Uranium-235 nucleus.
  2. The nucleus becomes unstable and splits into two smaller daughter nuclei.
  3. Two or three neutrons are also released, along with a lot of energy (in the form of kinetic energy of the fragments).

Chain Reactions

The neutrons released in the first split can go on to hit other Uranium-235 nuclei. This causes them to split and release even more neutrons. This is called a chain reaction. In a nuclear reactor, this is controlled using boron control rods (which absorb excess neutrons) to ensure the energy is released at a steady, safe rate.

Physics-Only: Nuclear Fusion

Nuclear fusion is the opposite of fission. It involves joining two small, light nuclei (usually isotopes of Hydrogen) to create a larger, heavier nucleus (Helium).

  • Energy Release: Fusion releases even more energy than fission! This is the process that powers the Sun and stars.
  • The Challenge: Fusion is very hard to do on Earth because nuclei are positively charged. Since "like charges repel," the nuclei push away from each other (electrostatic repulsion).
  • Conditions Needed: To overcome this repulsion and get the nuclei to fuse, we need extremely high temperatures and high pressures. This makes building fusion power stations very difficult and expensive.

Key Takeaway: Fission is splitting (used in power plants today); Fusion is joining (happens in stars, very hard to do on Earth).

Chapter Summary & Quick Review

Dangers: Irradiation is exposure; contamination is getting radioactive "stuff" on you. Always use shielding, distance, and time.

Medical (P-only): Gamma for tracers (short half-life); PET scanners use positron/electron annihilation; radiotherapy kills cancer.

Fission (P-only): Splitting heavy nuclei (\(^{235}\text{U}\)) using neutrons to release energy in a chain reaction.

Fusion (P-only): Joining light nuclei to make heavier ones. Requires high temp/pressure to overcome repulsion.

Remember: You have the formula sheet for Paper 1, but understanding these concepts will help you explain "how" and "why" in those longer 6-mark questions!