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14 Cards in this Set
- Front
- Back
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Random definition |
Cannot be predicted |
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Ionising Radiation Penetration |
Alpha - Paper or a few cm of air
Beta - ~3mm aluminium
Gamma - many cm of lead, several m of concrete |
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Alpha Particles |
- Slow & massive - Strongly positive - Quickly ionises many atoms (~10,000 per particle) - Suitable for smoke alarms: allow current to flow, wont travel very far |
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Beta-minus Particles |
- Faster & lower mass than alpha - Less interactions (~100 per particle) - Less damage to tissue than alpha - Can be used to target and kill cancerous cells without harming surrounding tissue much |
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Gamma |
- Very weakly ionising - Little damage to tissue - So used for diagnostic techniques in medicine (e.g. PET Scans) |
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Sources of Background Radiation (highest to lowest) |
- The air: Radon gas released from rocks - α - Ground & Buildings: all rocks have radioactive isotopes - Cosmic radiation: particles from space (often HE protons) collide with particles in upper atmosphere and produce nuclear radiation - Living things: all contain some Carbon-14 - Man-made: medical & industrial (tiny fraction) |
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Background Radiation in Measurements |
Need to subtract the reading of BR when taking readings from radioactive sources
Applies also when using graphs to measure half life |
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Half Life definition |
Average time it takes for the number of undecayed atoms of an isotope to halve |
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Uses of Radioactive Isotopes |
- Diagnose and treat medical problems, sterilise food/equipment, smoke alarms - Radiocarbon dating |
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Carbon Dating |
- Works only with once living material - Living plants take in some Carbon-14 - When they die C14 activity begins to fall with a half life of around 5730 years - By measuring activity and comparing to the composition of the atmosphere at the time of living the age of the sample can be found - Cannot be used for samples >60,000 years old as activity too low |
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Spontaneous |
A event or process occurring without apparent external cause |
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Background radiation
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Ionizing radiation emitted from a variety of natural and artificial radiation sources
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Corrected Count Rate
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A count rate of a sample that has accounted for background radiation (i.e. taken it away from the raw reading)
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Carbon Dating Assumptions
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- The ratio of C12 to C14 in the atmosphere was similar during the organism's life as it is today - Production of C14 depends upon cosmic radiation reaching the upper atmosphere so can vary over time |
