Question 1

What is the difference between radioactive contamination and irradiation?

Accepted Answer

Contamination occurs when radioactive material is deposited on or inside an object or person, making them radioactive. Irradiation is when an object is exposed to radiation but does not become radioactive itself. Contamination is more dangerous because it can be ingested or inhaled and continues to emit radiation, whereas irradiation stops once the source is removed.

Question 2

How do you calculate half-life from a graph?

Accepted Answer

To find half-life from a graph of activity against time, choose a starting activity value (e.g., 100 counts per minute). Find the time when the activity has halved (50 counts per minute). The difference in time is one half-life. Repeat for another halving (e.g., 50 to 25) to confirm consistency. The half-life is constant for a given isotope.

Question 3

Why is alpha radiation used in smoke detectors?

Accepted Answer

Alpha radiation is used because it is highly ionising and has a short range (a few cm in air). In a smoke detector, alpha particles ionise the air between two electrodes, allowing a small current to flow. Smoke particles absorb the alpha particles, reducing ionisation and the current, which triggers the alarm. The short range ensures safety as the alpha particles cannot escape the detector.

Question 4

What is background radiation and why is it important to measure it?

Accepted Answer

Background radiation is the low-level radiation present in the environment from natural sources (e.g., radon gas, cosmic rays, rocks) and artificial sources (e.g., medical waste, nuclear fallout). It is important to measure it before conducting experiments with radioactive sources so that the measured count rate can be corrected by subtracting the background count. This ensures accurate results.

Question 5

Can you become radioactive from having an X-ray?

Accepted Answer

No, having an X-ray does not make you radioactive. X-rays are a form of electromagnetic radiation (like gamma rays) that pass through your body. You are irradiated during the X-ray, but you do not become a source of radiation. The X-ray machine stops emitting radiation once the exposure ends.

Question 6

What is the difference between nuclear fission and radioactive decay?

Accepted Answer

Nuclear fission is the splitting of a large, unstable nucleus (e.g., uranium-235) into two smaller nuclei, releasing energy and neutrons. It is a controlled chain reaction used in nuclear power plants. Radioactive decay is the spontaneous emission of radiation from an unstable nucleus to become more stable. Decay is random and cannot be controlled, whereas fission is induced by neutron bombardment.

Topic 6 – Radioactivity

Topic Overview

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Related Topics in EDEXCEL GCSE Physics

Topic 1 – Key concepts of physics

Topic 10 – Electricity and circuits

Topic 11 – Static electricity

Topic 12 – Magnetism and the motor effect

How to Revise Topic 6 – Radioactivity — Edexcel GCSE Physics

Examiner Tips for Topic 6 – Radioactivity

Common Mistakes in Topic 6 – Radioactivity

Key Marking Points