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Chapter 25 - Radioactivity - Coggle Diagram
Chapter 25 - Radioactivity
Radiation
Alpha, beta, and gamma are ionising as they can remove electrons from atoms, leaving positive ions
Cloud chamber contains air saturated with vapour at low temperature and can detect radiation
When air molecules are ionisde, liquid condenses onto ions to leave tracks of droplets marking path of radiation
Alpha radiaiton - consists of alpha particles which is a helium nucleus
Beta radiaiton - fast moving electrons (minus) or positrons (plus)
Gamma - high energy photons
Electric and magnetic fields
Electric
Beta minus particles (electrons) are deflected towards positive plate
Beta plus particles (positrons) and alpha particles are deflected towards negative plate
Alpha particles are deflected less than beta particles as their mass is lighter
Gamma rays aren't deflected as they're uncharged
Magnetic
Direction of force on particles can be determined using Fleming's left hand rule
uncharged gamma rays aren't deflected
Absorption
Experiment
GM tube is kept at a fixed distance from radioactive source, and is behind an absorber material
Background radiation must be measured before experiment (count rate without source present)
Count rate of absorber is determined, you can use different thickness of same absorber to see how it effects count rate
Subtract background count rate from measured count rate
large mass and charge of alpha particles are strong ioniseres, so have short range in air and air absorbed within a few cm of air, paper stops them
Small mass and charge of beta particles make them less ionising than alpha particles, their range is 1m in air, 1-3mm of aluminium stops them
Gamma rays have no charge so are least ionising. They're only stopped by a few centimetres of lead
Dangers
Can damage living cells
Always use tongs when handling, never bare hands
Stroed in lead-lined containers
Alpha decay
Energy is also released
Occurs in very large isotopes
Beta decay
Minus
weak nuclear force is responsible for one of neutrons decaying into a proton
Nucei have too many neutrons for stability
Plus
Nuclei have too many protons
Weak force initiates one proton transforming into a neutron
Gamma decay
Gamma photons are emitted if a nucleus has surplus energy
Composition of nucleus remain the same
