Radioactivity occurs when the nuclei of unstable atoms decay and emit radiation. There are three main types of radiation: alpha, beta, and gamma. Alpha particles consist of two protons and two neutrons, beta particles are electrons or positrons, and gamma radiation consists of electromagnetic waves. The rate of radioactive decay is random, but the half-life of a radioactive isotope is the time it takes for half the nuclei in a sample to decay. Radioactivity has industrial applications and background radiation comes from natural and man-made sources.

1. Radioactivity
Medical Physics
Unit 20 strand 1 (part)

2. To achieve a pass grade the To achieve a merit grade the
evidence must show that the evidence must show that, in
learner is able to: addition to the pass criteria,
the learner is able to:
P1 describe radioactivity, M1 explain the random
including atomic structure nature of decay and how it
relates to half-life

3. What is radiation?
The nuclei of some atoms are unstable. In order to achieve stability they
emit radiation.
These materials are called radionuclides.
They are radioactive.
Radioactivity is a nuclear process – it is not a chemical process. It is not
possible to control the rate of radioactive breakdown of a nuclei, it is a
random process
Radioactivity: industrial applications

4. Background radiation

5. Atomic structure
Atoms consist of a nucleus and electrons
The nucleus is made up of protons and neutrons
Blockbusters game

7. Characteristics of alpha, beta (β+ and β–) and gamma
radiations
There are three types of radiation that can be emitted from a nucleus of an
unstable atom.
Alpha (α)and beta (β) are particles of matter
Gamma (γ) rays are photon of electromagnetic radiation, with a higher
frequency than an x-ray.

8. Characteristics of alpha, beta (β+ and β–) and gamma
radiations
Particle Constituent Charge Mass
Alpha (α) Helium nucleus +2 4
2 protons and 2
neutrons
Beta- minus (β-) Electron -1 Negligible
Beta-plus (β+) Positron +1 Negligible
Gamma (γ) Short-wave, high 0 0
frequency em wave

9. Particle Ionising Range Speed Affected by
magnetic field?
Alpha (α) Strong –easily pull Slow Yes
electrons off atoms
(10 000 ionisations
per particle)
Beta- minus (β-) Weakly (100 atoms Fast Yes
per particle)
Beta-plus (β+) Annihilated by electron – so zero range
Gamma (γ) Very weakly Speed of light No
Gamma radiation spreads out very quickly. Its intensity decreases by the inverse square law.

10. Characteristics of alpha, beta (β+ and β–) and gamma
radiations

11. •random nature of radioactive decay

12. • The half-life of a radioactive isotope is defined as the
time it takes for the number of nuclei of the isotope in a
sample to halve or the time it takes for the count rate
from a sample containing the isotope to fall to half its
initial level.

13. Half-life

19. Resources
Specific texts
Jean Pope Medical Physics: Imaging (Heineman Advanced Science )
Roger Muncaster Medical Physics (A-Level Physics) Cheltenham: Stanley Thornes
(Publishers) Ltd
Martin Hollins (1990) Medical Physics (University of Btah Macmillan Science 16-19
Project) Basingstoke: Macmillan
John Ball and Adrian Moore (1997 3rd edn) Essential Physics for Radiographers
Oxford: Blackwell
General Physics books
Keith Johnson, Simmone Hewett, Sue Holt, John Miller (2000) Advanced Physics for
You Cheltenham: Nelson Thornes.
Ch 27 on Radioactivity
Ken Dobson, David Grace and David Lovett (2002 2nd edn) Physics (Collins
Advanced Science)
Ch 19 Medical Physics
Claire Thomas and Julie Wakeling (ed.) AS-Level Physics The Revision Guide (CGP)