Physics OCR, P6

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What are radioactive elements?
elements emitting ionising radiation all the time
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Where can radioactive elements be found?
naturally in the environment, contributing to background radiation
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What is the structure of an atom?
an atom has a nucleus, made of protons and neutrons, which is surrounded by shells containing electrons
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What did the results of the Rutherford-Geiger-Marsden alpha particle scattering experiment show?
atoms consist largely of empty space, with a small dense nucleus. The nucleus is positively charged and electrons are arranged around nucleus with lots of space between
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How are protons and neutrons held together in the nucleus?
by a strong force which balances the repulsive electrostatic force between the protons
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What is nuclear fusion?
when hydrogen nuclei fuse into helium nuclei, releasing energy
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What is Einstein's equation? and what is it used for?
E=mc². Used to calculate the energy released during nuclear fusion and fission
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What does every atom of the same element have the same number of?
protons but the number of neutrons may differ
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What is an isotope?
forms of the same element with different numbers of neutrons
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What are the three types of ionising radiation?
alpha (particles consist of two protons and two neutrons), beta (particles are identical to electrons and gamma are all emitted by radioactive materials
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What are the penetration properties of alpha?
absorbed by paper. Strong ionising power
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What are the penetration properties of beta?
passes through paper but absorbed by aluminium. Reasonable ionising power
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What are the penetration properties of gamma?
very penertrating and needs lots of lead or concrete to absorb most of it. Poor ionising power
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When is ionising radiation emitted?
when the nucleus of an unstable atom decays. The type of radioactive decay depends on why the nucleus is unstable
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Why is the process of decay important?
helps the atom become more stable.
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What happens when the number of protons during radioactive decay changes?
the element changes to another type
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What happens to radioactive sources over time?
the activity of radioactive sources decreases
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What does the term half-life mean?
the half-life of a substance is the time it takes for its radioactivity to halve. Radioactive elements have a wide range of half-life values
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Why is ionising radiation dangerous?
it can damage living cells, which may be killed or may become cancerous
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What is ionising radiation able to do?
ionising radiation is able to break molecules into bits (called ions), which can then take part in other chemical reactions
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What are uses of ionising radiation?
to treat cancer, to sterilise surgical instruments, to sterilise food, as a tracer in the body
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What is a radiation dose (in sieverts)?
a measure of the possible harm done to your body
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What is a sievert based on?
the type and amount of radiation absorbed
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How are radioactive materials exposed to people?
by irradiation and contamination
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What is the main source to our constant irradiation and contamination by radioactive materials?
background radiation
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What is the level for background radiation?
dose of around 3 millisieverts per year or 25 counts per minute with a standard detector
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How are people in jobs involving using radioactive materials (workers in a nuclear power stations and radiographers) kept safe?
their exposure is carefully monitored
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What risks does alpha radiation carry?
most dangerous if the source is inside the body, all radiation will be absorbed by cells in the body
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What risks does beta radiation carry?
most dangerous if the source is outside the body. It can penetrate the outer layer of skin and damage internal organs
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What risks does gamma radiation carry?
can cause harm if absorbed by the cells, but is not very ionising and can pass straight through the body causing no damage at all
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What is a nuclear fuel?
a fuel in which energy is released by changes in the nucleus
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What happens in nuclear fission?
a neutron splits a large and unstable nucleus (limited to uranium and plutonium) into two smaller parts, roughly equal in size, releasing more neutrons
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What is significant about the amount of energy released during nuclear fission?
the amount of energy released during nuclear fission is much greater than that released in a chemical reaction involving a similar mass of material
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How is the nuclear fission process in nuclear power stations controlled?
nuclear reactor controls the chain reaction so that energy is steadily released. Control rods, made of boron, absorb neutrons, preventing the chain reaction getting out of control.
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How does nuclear fission in a nuclear reactor work?
nuclear power stations use fission to generate heat needed to produce steam. Fission occurs in fuel rods, causing them to get hot. Coolant fluid pumped through reactor heats up and is then used in the heat exchanger to turn water into steam.
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In a nuclear reactor, what changes the amount of fission that takes place?
moving the control rods in and out of the reactor core
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What do nuclear power stations produce?
radioactive waste
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How is nuclear waste categorised?
as high level, intermediate level and low level, which relates to disposal methods
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Other cards in this set

Card 2

Front

Where can radioactive elements be found?

Back

naturally in the environment, contributing to background radiation

Card 3

Front

What is the structure of an atom?

Back

Preview of the front of card 3

Card 4

Front

What did the results of the Rutherford-Geiger-Marsden alpha particle scattering experiment show?

Back

Preview of the front of card 4

Card 5

Front

How are protons and neutrons held together in the nucleus?

Back

Preview of the front of card 5
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