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Syllabus points “Some nuclides are unstable and spontaneously decay,
emitting alpha, beta (+/-) and/or gamma radiation over time until they become stable nuclides”
“Alpha, beta and gamma radiation have different natures, properties and effects”
Learning goals Define:
Alpha particle
Beta particle
Gamma radiation
Ionisation
Penetration
Compare and contrast the structure of alpha, beta and gamma radiation
Compare and contrast the properties of alpha, beta and gamma radiation (including ionising ability and penetration rate)
Describe how to shield alpha, beta and gamma radiation
Identify that in a nuclear reaction both atomic and mass numbers are conserved
Construct nuclear decay equations
Balance nuclear decay equations
Interpret nuclear decay equations
Recall which decays can occur simultaneously and which cannot
Writing nuclear equations
Mass is always conserved
Charge is always conserved
Use the chemical symbols for the elements
E.g.
Parent nucleus Daughter nucleus
Types of radiation
In a radioisotope the nucleus is unstable and may spontaneously emit radiation to become more stable
There are three different types of radiation: Alpha - α
Beta - β
Gamma - γ
The energy of radiation can be measured in electron-volts(eV)
where 1 eV = 1.6 × 10-19 J
Alpha radiation
Represented by the lowercase Greek letter ‘alpha’ - α
Consists of 2 protons and 2 neutrons, it is a helium nucleus
Positively charged (+2)
Usually emitted by heavier elements such as uranium and radium
Can be absorbed by a sheet of paper
Range in air is only a few centimetres
Emitted at a velocity of 5-7% the speed of light
α
Alpha decay - Example
atomic number decreases by 2
mass number decreases by 4
238
92
234
90 2
4
U Th + α
Alpha decay - General
A
Z
A-4
Z-2 2
4
X Y + α
Your Turn Complete the following nuclear equations:
Your Turn Complete the following nuclear equations:
Beta radiation
Represented by the lowercase Greek letter ‘beta’ - β
Consists of 1 electron
Negatively charged (-1)
Can be absorbed by 3.5 cm of lead or a sheet of aluminium
Range in air is a few metres
Emitted with a velocity of 30-90% speed of light
β
Beta decay - Example
atomic number increases by 1
mass number remains the same
14
6
14
7C N + β
-1
0
Beta decay - General
A
Z
A
Z+1X Y + β
-1
0
Your Turn
Complete the following nuclear equations:
Your Turn Complete the following nuclear equations:
Gamma radiation
Gamma radiation electromagnetic wave (not a particle)
No charge, it’s a type of energy, not a particle
Absorbed by several cm of lead
Range in air is almost unlimited
Electromagnetic wave, so it travels a the speed of light
γ
From: http://en.wikipedia.org/wiki/Electromagnetic_spectrum#mediaviewer/File:EM_Spectrum_Properties_edit.svg
Gamma decay
atomic number remains the same
mass number remains the same
60
28
60
28Ni Ni + γ
Your TurnWrite the following nuclear equations,
make sure they are balanced:a)Plutonium-244 decays by alpha emission
b)The decay of nitrogen-16 by beta emission
c)Uranium-235 loses an alpha particle
d)Phosphorus emits a beta particle
e)Thallium decays through emitting gamma rays
Your Turn
Combinations
When an atom decays it can emit more than one type of radiation at the same time
Gamma radiation is not normally emitted alone, it usually accompanies alpha or beta radiation
α γ β γ α βE.g.
Penetration & ionisation Penetration = how deep radiation can travel
into a material
Ionising ability = ability of radiation to create ions
Alp
ha • Slow speed
• Relatively large • +2 charge• Can pick up loose
electrons to become a He atom
• Not much energy• Easy to stop• High ionising
ability• Low penetrating
ability
Bet
a • Faster than alpha• Small particle• -1 charge• Repelled by
electron cloud of other atoms
• More energy than alpha
• Do not ionise as readily as alpha
• More penetrating than alpha
Gam
ma • Moves at the
speed of light• No charge• Only interacts
when it directly hits a nucleus/electron, rare occurrence
• Low ionising ability
• High penetrating ability
Resources
AV Bozeman Science - Radiation and Radioactive Decay
(10:55) Tyler DeWitt – Alpha Decay (13:07) Tyler DeWitt – Beta Decay (9:58) Khan Academy – Alpha, beta and gamma decay (8:06)Further Reading BBC Bitesize Science – simple recap of important info ARPANSA website – info on alpha, beta and gamma
radiation pHet simulation - Alpha Decay pHet simulation - Beta Decay
How did you go? Define:
Alpha particle
Beta particle
Gamma radiation
Ionisation
Penetration
Compare and contrast the structure of alpha, beta and gamma radiation
Compare and contrast the properties of alpha, beta and gamma radiation (including ionising ability and penetration rate)
Describe how to shield alpha, beta and gamma radiation
Identify that in a nuclear reaction both atomic and mass numbers are conserved
Construct nuclear decay equations
Balance nuclear decay equations
Interpret nuclear decay equations
Recall which decays can occur simultaneously and which cannot
