Radioactivity

Medical Physics

Unit 20 strand 1 (part)

To achieve a pass grade the evidence must show that thelearner is able to:

P1 describe radioactivity,including atomic structure

To achieve a merit grade theevidence must show that, inaddition to the pass criteria,the learner is able to:

M1 explain the random nature of decay and how it relates to half-life

Radioactivity: industrial applications

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

Background radiation

Atomic structure

Atoms consist of a nucleus and electronsThe nucleus is made up of protons and neutrons

Blockbusters game

Characteristics of alpha, beta (β+ and β–) and gamma radiationsThere are three types of radiation that can be emitted from a nucleus of an unstable atom.

Alpha (α)and beta (β) are particles of matterGamma (γ) rays are photon of electromagnetic radiation, with a higher frequency than an x-ray.

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

Particle Constituent Charge MassAlpha (α) Helium nucleus

2 protons and 2

neutrons

+2 4

Beta- minus (β-) Electron -1 Negligible

Beta-plus (β+) Positron +1 Negligible

Gamma (γ) Short-wave, high

frequency em wave

0 0

Particle Ionising Range Speed Affected by

magnetic field?

Alpha (α) Strong –easily pull

electrons off atoms

(10 000 ionisations

per particle)

Slow Yes

Beta- minus (β-) Weakly (100 atoms

per particle)

Fast Yes

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.

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

•random nature of radioactive decay

• 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.

Half-life

ResourcesSpecific textsJean Pope Medical Physics: Imaging (Heineman Advanced Science )Roger Muncaster Medical Physics (A-Level Physics) Cheltenham: Stanley Thornes(Publishers) LtdMartin Hollins (1990) Medical Physics (University of Btah Macmillan Science 16-19 Project) Basingstoke: MacmillanJohn Ball and Adrian Moore (1997 3rd edn) Essential Physics for RadiographersOxford: Blackwell

General Physics booksKeith Johnson, Simmone Hewett, Sue Holt, John Miller (2000) Advanced Physics for You Cheltenham: Nelson Thornes.Ch 27 on RadioactivityKen Dobson, David Grace and David Lovett (2002 2nd edn) Physics (Collins Advanced Science) Ch 19 Medical PhysicsClaire Thomas and Julie Wakeling (ed.) AS-Level Physics The Revision Guide (CGP)