P6 - Radioactive Materials Flashcards
Rutherford-Geiger-Marsden experiment results…
- Was done to find results supporting the plum pudding model of the atom
- Results were unexpected: scientists expected all alpha particles to go through the thin foil but some emerged at different angles and some were deflected back
- 1905
Rutherford-Geiger-Marsden experiment conclusions…
- Positively charged alpha particles were being repeller by a tiny concentration of positive charge in the foil atoms
- The plum pudding model was replaced with the nuclear model
- most of the space taken up by atoms must be empty
- the majority of the mass is in the nucleus
Protons and neutrons are held together in the nucleus by…
A strong force which balances the repulsive electrostatic force between the protons
Nuclear fusion is..
When hydrogen nuclei are brought close enough together they have the ability to fuse and create helium nuclei and release energy
E=mc^2 is used to calculate…
Energy released during nuclear fission and fusion
An isotope is…
A form of an element with a different number of neutrons (every atom of an element has the same number of protons)
The behaviour of radioactive materials…
Cannot be changed by chemical or physical process
The three types of ionising radiation are…
Alpha, beta and gamma
Alpha particles are…
2 protons and 2 neutrons, identical to helium nuclei
Beta particles are…
A high speed electron
Alpha radiation is…
Highly ionising and weakly penetrating, it can be stopped by a piece of paper.
Beta radiation is…
Moderately ionising and moderately penetrating, it can be stopped by a thin piece of aluminium.
Gamma radiation is…
Weakly ionising and highly penetrating, high levels can be stopped only by many cm of lead of many metres of concrete
Over time the radioactivity of a source _____
Decreases
Half life is…
- The time it takes for a number of atoms in a sample to halve
- The time it takes for the activity of a source of radiation to fall by half
Radioactive decay is…
When the unstable nuclei of radioactive atoms break down and change into a new type of atom. For example carbon-14 decays to nitrogen-14 when it emits beta radiation
Ionising radiation is able to…
Break down molecules into ions which can then take part in other chemical reactions
Ionising radiation can be used to…
- treat cancer
- sterilise surgical instruments
- sterilise food
- as a tracer in the body
Ionising damages living cells and can kill them or cause them to become cancerous. Radiation dose is…
A measure of the possible harm done to your body and is measured in sieverts
Irradiation is…
When the radiation from the material can damage the cells of a person directly and the source is outside the body
Contamination is…
When radioactive material is swallowed or breathed in and whilst inside the body the radiation it emits produces damage
The main sources of background radiation are…
- cosmic rays
- radon gas
- food and drink
People regularly exposed to radiation include…
Radiographers and those that work in nuclear power plants. Their exposure is carefully monitored.
Nuclear fuel is…
A fuel in which energy is released by changes in the nucleus
In nuclear fission…
A neutron splits a large unstable nucleus( U or Pu) into two smaller parts, roughly equal in size, and releases 3 more neutrons
The amount of energy released in nuclear fission is ________ than that produced in a chemical reaction involving a similar mass of material
Greater
Nuclear fission process is controlled in power stations with…
Boron fuel rods which absorb some of the released nuclei and limit the effects of the chain reaction so energy is released at a steady rate and not exponentially. The lower they are lowered the more nuclei they can absorb. Coolant is circulated through the reactor core to remove the heat.
High level waste is disposed of…
Underwater in large pools for 20 years then placed in storage cakes in purpose- built underground stores to remove the heat produced. It is stored as intermediate waste once it decays into such.
Intermediate level waste is disposed of…
Mixed with concrete then put in stainless steel drums in a purpose built store
Low level waste is disposed of…
Put in drums and surrounded by concrete then put into clay lined landfill sites
Low level waste examples are…
Contaminated equipment, materials and protective clothing
Medium level waste examples are…
Components from nuclear reactors, radioactive sources used in medicine and research
High level waste examples are…
Used nuclear fuel and chemicals from reprocessing fuels
Benefits of nuclear fuels…
Do not produce carbon dioxide
Disadvantages of nuclear fuels…
Non-renewable energy sources, large amounts of radioactive waste that remains radioactive for many years
Radioactive elements…
- Constantly emit ionising radiation
- some are found naturally and contribute to background radiation
