OCR GCSE Physics B (Twenty First Century)
OCR GCSE Physics B P5 Radioactive Materials Exam Questions
Free OCR GCSE Physics B revision for P5 Radioactive Materials: what you need to know, common mistakes and exam-style questions with answers. Covers atomic models, isotopes, alpha, beta and gamma radiation, nuclear equations, half-life, contamination, irradiation, medical uses, fission and fusion.
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About OCR GCSE Physics B P5 Radioactive Materials
Chapter P5 explores the nucleus and the radiation that unstable nuclei emit. On OCR Physics B you trace how the model of the atom developed, describe isotopes using nuclear notation and explain alpha, beta, gamma and neutron emission with balanced nuclear equations. You then use half-life to describe the random nature of decay, compare contamination with irradiation and evaluate medical uses of radiation. Separate physics adds nuclear fission, chain reactions and fusion. P5 links to ionising radiation in P1 and energy resources in P2. Examiners test nuclear equations, half-life calculations from graphs and explanations of hazards.
What you need to know
- P5.1 The atom and isotopes An atom has a tiny positive nucleus containing protons and neutrons, with electrons around it; almost all the mass is in the nucleus. Isotopes of an element have the same number of protons but different numbers of neutrons.
- P5.1 Radioactive decay Unstable nuclei emit alpha particles (2 protons and 2 neutrons), beta particles (fast electrons from the nucleus), gamma rays or neutrons. Alpha decay lowers the mass number by 4 and atomic number by 2; beta decay raises the atomic number by 1 with no change in mass number.
- P5.1 Half-life Decay is random, but the half-life is the time for the activity, or the number of unstable nuclei, to halve. After n half-lives the activity has fallen to (1/2)^n of its starting value.
- P5.2 Using radiation safely Alpha is stopped by paper, beta by a few mm of aluminium and gamma is reduced by thick lead. Irradiation is exposure to radiation from outside; contamination is when radioactive material gets onto or into the body. Tracers and radiotherapy are medical uses.
- P5.3 Fission and fusion Separate physics only: in fission a large nucleus splits into two smaller nuclei, releasing energy and neutrons that can cause a chain reaction. In fusion light nuclei join, and some mass is converted into energy.
Common mistakes in P5 Radioactive Materials
- Saying an irradiated object becomes radioactive. Irradiation does not make an object radioactive; contamination means radioactive atoms are present on or in it.
- Thinking beta particles come from the electron shells. A beta particle is an electron emitted from the nucleus when a neutron changes into a proton.
- Saying half-life is half the time it takes for all the nuclei to decay. It is the time for the activity or number of unstable nuclei to halve.
- Unbalanced nuclear equations. Check that mass numbers and atomic numbers each add up on both sides.
- Saying gamma is the most dangerous inside the body. Alpha is most hazardous inside the body because it is the most strongly ionising.
Try three P5 Radioactive Materials exam-style questions
1. Uranium-238 (atomic number 92) decays by alpha emission to thorium. Give the mass number and atomic number of the thorium nucleus. (2 marks)
Show the mark scheme answer
Mass number 238 - 4 = 234; atomic number 92 - 2 = 90.
2. A sample has an activity of 800 Bq and a half-life of 6 hours. Calculate its activity after 18 hours. (2 marks)
Show the mark scheme answer
18 / 6 = 3 half-lives; 800 / 2 / 2 / 2 = 100 Bq.
3. Explain the difference between irradiation and contamination, and why contamination with an alpha source is particularly hazardous. (3 marks)
Show the mark scheme answer
Irradiation is exposure to radiation from a source outside the body; contamination is when the radioactive material is on or inside the body so exposure continues; alpha is highly ionising so it damages nearby cells strongly once inside the body.
P5 Radioactive Materials FAQs
What does OCR Physics B P5 Radioactive Materials cover?
It covers atomic structure and isotopes, alpha, beta, gamma and neutron emission, nuclear equations, half-life, contamination and irradiation and medical uses of radiation. Separate physics adds fission and fusion.
Which paper is it examined in?
OCR Physics B has two papers at each tier, Breadth in physics and Depth in physics, and both can assess content from every chapter, so P5 can appear on either paper.
How do I find half-life from a graph?
Read the starting activity, find half that value on the y-axis, then read across to the curve and down to the time axis. Repeat from a different starting point to check.
