Radioactivity
- Created by: HeHeHe24
- Created on: 05-12-19 19:54
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- Radioactivity
- Ionising radiation
- Alpha (He-4) Q=+2e
- large rest mass and charge
- interact with particles - strong ionisation
- short range in air - least penetrating as a piece of paper completely absorbs
- Beta - fast moving electron or positron
- small rest mass and charge
- less ionising - reduced charge
- larger range in air - absorbed by a few mm of Al
- Gamma radiation - high energy photon
- no charge or rest mass so are the least ionising
- few cm of Pb block stops it so it is the most penetrating
- thickness increases, the count rate decreases exponentially
- can be good for us
- X-rays
- CT scans
- radiotherapy to treat cancers
- dangers
- cause ionisation
- damage living cells - cause cancer
- Alpha (He-4) Q=+2e
- Detect ionising radiation
- Geiger-Müller tube
- measure the background radiation first to find the true count rate
- need to keep GM tube at a fixed distance away from source
- determine count rate from the absorber and change thickness of to see effect
- precautions
- Ensure it is kept in a lead lined box to minimise radiation exposure
- ensure direction of travel isn't towards anyone
- use tongs that are 15cm long to keep at a fixed distance away from the body
- always wear gloves
- Geiger-Müller tube
- Background radiation
- radiation around us from day to day
- examples
- food (bananas)
- rocks (graphene)
- gases (radon)
- soil
- Nuclear Decay equations
- transmutation - nuclei of radium atoms emit alpha particles and change into nuclei of radon atoms
- parent nuclei - nuclei before decay
- daughter nuclei - nuclei after decay
- proton and nucleon number must be conserved
- alpha - release a alpha particle
- beta minus decay - emit a electron and an electron antineutrino
- weak nuclear force due to quark flavour change
- Beta plus decay - emits a positron and a electron neutrino
- weak nuclear force due to quark flavour change
- Gamma decay - releases a high energy photon due to surplus energy
- Nuclear stability
- Becquerel - Bq : unit of activity = 1 disintegration per second
- strong nuclear force
- hold nucleons together to stabilise the nucleus
- larger nuclei
- need more protons to hold particle together
- larger strong nuclear force
- belt of stability
- Below
- too many neutrons
- repulsive
- B- decay
- above
- too many protons
- Untitled
- Below
- Half life
- nature of radioactive decay
- random
- cannot predict which nuclei will decay next
- spontaneous
- decay isnt effected by presence of other nuclei or external factors
- random
- average time it takes for half the nuclei to decay
- nature of radioactive decay
- Activity
- rate at which nuclei decay
- number of alpha, beta or gamma photons emitted per unit time
- Unit - Becquerel (Bq)
- depends on
- number of undecayed nuclei present in source
- half life of isotope
- Decay constant
- probability of an individual nucleus decaying per unit time
- Radioactive carbon dating
- all living organisms contain carbon
- radio of C-12 to C-14 is almost constant
- but as organism dies it stops releasing and taking in carbon
- C-14 continues today
- ratio decreases over time
- determine time by comparing activities
- limitations
- assumes ratio is constant over time
- increased CO2 emission would reduce - burning fossil fuels & natural disasters
- Ionising radiation
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