Uses and hazards

Radioactive materials are a natural part of our environment, but they can also be highly dangerous if not handled correctly. However, when we understand how they behave, we can harness them for life-saving medicine, safety devices, and low-carbon energy.

This guide covers everything you need to know about radioactive hazards, how we use radiation in medicine, and the powerful nuclear processes of fission and fusion.

What you'll learn

• The vital difference between being irradiated and being contaminated.
• How an isotope's half-life and radiation type determine its hazard level.
• How nuclear radiation is used to diagnose and treat illnesses in medicine.
• How nuclear fission and fusion release vast amounts of energy by manipulating atomic nuclei.

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1. Irradiation vs. Contamination

A common misconception is that anything exposed to radiation automatically becomes radioactive. To understand why this is false, we must distinguish between irradiation and contamination.

Comparing the Hazards

The hazard to a person depends heavily on whether they are irradiated or contaminated, and what type of radiation is involved (alpha, beta, or gamma):

• When irradiated from an external source:

  • Gamma and beta radiation are the most hazardous because they are highly penetrating. They can pass through clothing and skin to reach vital organs.
  • Alpha radiation is the least hazardous because it has a very low penetrating power. It is easily blocked by the skin or a few centimetres of air, meaning it cannot reach deep internal organs.

• When contaminated internally (ingested or inhaled):

  • Alpha radiation becomes extremely hazardous. Because alpha particles are highly ionising, they cause intense localized damage to cells and DNA within a very small area, leading to mutations and cancer.
  • Beta and gamma radiation are less hazardous internally because they are less ionising. A significant portion of their energy escapes the body without being absorbed by tissues.

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2. Half-Life and Radioactive Hazards

(Note: The remaining sections of this topic are for students taking Separate GCSE Physics (J249) only. They do not appear in Combined Science).

The danger of a radioactive source is not constant—it changes over time depending on the source's half-life (the time it takes for half of the unstable nuclei in a sample to decay).

Short Half-Life vs. Long Half-Life

• Short half-life: The activity of the source starts very high, meaning it emits intense radiation in a short space of time. While it is initially extremely hazardous, the danger passes quickly as the nuclei decay rapidly.
• Long half-life: The activity remains low but stable over a very long period. Although it emits less radiation per second, it remains radioactive and hazardous for decades, centuries, or even millennia, making long-term storage and disposal a major challenge.

Everyday Application: Smoke Detectors

Household smoke detectors use an alpha-emitting isotope called Americium-241 (${}^{241}Am$).

1. Why Alpha? Alpha particles ionise the air inside a small chamber in the detector, creating a small electrical current. If smoke particles enter, they absorb the alpha particles, breaking the current and triggering the alarm. Alpha radiation is perfect because its low penetration means it cannot escape the plastic housing of the alarm, making it completely safe for residents.
2. Why a Long Half-Life? Americium-241 has a half-life of 432 years. This is essential because the activity of the source remains virtually constant over your lifetime. If it had a short half-life of a few weeks, the detector would lose its activity quickly, and you would constantly have to replace the radioactive source!

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3. Medical Uses of Nuclear Radiation

Nuclear radiation is an invaluable tool in modern medicine. It is used in two main ways: exploration (diagnosing issues) and treatment (destroying unwanted tissues).

Exploring Internal Organs (Radioactive Tracers)

To examine how an internal organ is functioning without surgery, doctors inject or have the patient swallow a radioactive isotope called a medical tracer.

• The tracer travels to specific organs.
• A detector outside the body (such as a gamma camera) tracks where the tracer goes and builds an image.
• Choosing the right isotope:
  • It must emit gamma radiation because gamma is highly penetrating and can easily pass out of the patient's body to be detected. Alpha or beta would be absorbed by body tissues, harming the patient and failing to reach the detector.
  • It must have a short half-life (typically a few hours) so that it decays quickly after the scan is complete, minimizing the radiation dose the patient receives.

Control and Destruction of Unwanted Tissue (Radiotherapy)

Cancerous tumours can be treated using high doses of radiation to kill the cancer cells. This is called radiotherapy.

• External radiotherapy: High-energy gamma rays are aimed directly at the tumour from multiple angles. This concentrates the radiation dose at the tumour while minimizing damage to surrounding healthy tissue.
• Internal radiotherapy: An beta or alpha emitter is placed directly inside or next to the tumour (e.g., using radioactive implants or targeted drugs). Alpha emitters are highly effective here because their short range means they destroy the targeted cancer cells without damaging healthy tissue further away.

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4. Nuclear Fission

Nuclear power stations generate electricity by tapping into the energy stored inside atomic nuclei. The main process they use is nuclear fission.

How Fission Works

Fission rarely happens spontaneously. For fission to occur, a heavy, unstable nucleus must usually first absorb a neutron.

1. A slow-moving neutron is absorbed by a Uranium-235 (${}^{235}U$) nucleus.
2. This makes the nucleus extremely unstable, causing it to split into two smaller daughter nuclei (often isotopes of barium and krypton).
3. The split releases two or three high-speed neutrons, along with a massive amount of energy carried away as kinetic energy of the particles and gamma radiation.

$${}_0^{1}n{+}_{92}^{235}U\to fission\; fragments+2or3{}_0^{1}n+energy$$

Chain Reactions

Because one fission event releases multiple neutrons, those neutrons can go on to be absorbed by other nearby Uranium-235 nuclei. This causes further fission events, which release even more neutrons. This self-sustaining cycle is called a chain reaction.

• Controlled chain reactions: In a nuclear power reactor, control rods (made of materials like boron) absorb excess neutrons to keep the chain reaction steady, releasing energy at a safe, constant rate to boil water, spin turbines, and generate electricity.
• Uncontrolled chain reactions: If the reaction is not controlled, the number of fission events grows exponentially in fractions of a second. This releases an immense explosion of energy, which is how nuclear weapons work.

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5. Nuclear Fusion

There is another way to release nuclear energy: by doing the exact opposite of fission.

Mass to Energy Conversion

During nuclear fusion, the total mass of the resulting heavier nucleus is slightly less than the combined mass of the two starting light nuclei. This "lost" mass has been converted directly into energy, which is carried away as radiation.

$$Mass\; of\; Reactants>Mass\; of\; Products⟹Difference\; converted\; to\; Energy$$

This mass-to-energy conversion is described by Einstein's famous equation:

$$E=m{c}^2$$

The Challenge of Fusion

Fusion is the process that powers stars, including our Sun. In the Sun, hydrogen nuclei (protons) fuse to form helium nuclei.

However, replicating fusion on Earth to generate electricity is incredibly difficult because:

• Nuclei are positively charged (due to their protons), so they strongly repel each other (electrostatic repulsion).
• To overcome this repulsion and get close enough to fuse, the nuclei must be moving at extremely high speeds.
• This requires extremely high temperatures and pressures, which are incredibly difficult and expensive to contain safely in a power plant.

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