Studied by 2 peopleThe control rods, made from boron, are used to control the chain reaction. Boron atoms absorb neutrons without undergoing nuclear fission.
Why does lowering the control rods reduce the amount of energy released each second from the nuclear fuel?
neutrons are absorbed
there are fewer neutrons
chain reaction slows down
Energy is released from nuclear fuels by the process of nuclear fission.
This energy is used to generate electricity.
Describe how this energy is used to generate electricity.
Do not explain the nuclear fission process.
energy used to heat water and produce high pressure steam
the steam drives a turbine
Internal contamination of the human body means radioactive material is inside the human body.
Explain how the risk from internal contamination is different to the risk from external irradiation by a source of alpha radiation.
alpha radiation has low penetrating ability
alpha radiation is stopped by skin
internally, alpha radiation is absorbed by living tissue
alpha radiation is highly ionising
internal contamination will cause greater harm to cells
What is meant by the ‘random nature of radioactive decay’?
you cannot predict which nucleus will decay next
A polonium (Po) nucleus decays by emitting an alpha particle and forming a lead (Pb) nucleus.
Po → Pb + α
The lead (Pb) nucleus then decays by emitting a beta particle and forms a bismuth (Bi) nucleus.
Pb → Bi + β
The bismuth (Bi) nucleus then decays by emitting a beta particle and forms a polonium (Po) nucleus.
Bi → Po + β
Explain how these three decays result in a nucleus of the original element, polonium.
one alpha decay would decrease the proton number by 2
2 beta decays would increase the proton number by 2
so the proton number at the final nucleus would be the same as the original nucleus
Give one other man-made source of background radiation.
x rays
Nuclear fusion power stations will produce radioactive waste. This waste will have a much shorter half-life than the radioactive waste from a nuclear fission power station.
Explain the advantage of the radioactive waste having a shorter half-life.
activity decreases quickly therefore the risk of harm decreases quickly
Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous.
alpha radiation is highly ionising which means it can cause an increased risk of cancer until the radioactive material is removed
The smoke alarm stays off while alpha radiation reaches the detector.
Why does the alarm switch on when smoke particles enter the plastic casing?
smoke stops the alpha radiation
The smoke alarm would not work with a radiation source that emits beta or gamma radiation.
Explain why.
beta and gamma radiation will penetrate smoke and so no change would be detected
Explain why the radiation source inside the smoke alarm should have a long half-life.
a long half life means the count rate is approximately constant until 1.3 half lives the count rate is above 80 per second
Explain the ideal properties of a radioactive source for use in medical diagnosis.
a short half life as it means less damage is caused to the cells
low ionising power means there is also less damage to the cells
highly penetrating so it can be detected outside the body
emits gamma radiation
Describe the advantages of nuclear power compared with the use of shale gas to generate electricity.
no co2 emitted
no earthquakes
does not cause global warming
Explain how the paths of the alpha particles were used to develop the nuclear model of the atom.
most alpha particles passed straight through the atom which shows the atom is mostly space
very few alpha particles are deflected through a large angle which shows the atom contained a nucleus where the mass of the atom is concentrated
Explain how the distance at which an electron orbits the nucleus may be changed.
electrons may absorb electromagnetic radiation and move further from the nucleus to a higher energy level
Some substances are radioactive. They may emit alpha or beta particles.
Describe the characteristics of alpha particles and beta particles in terms of their:
• structure
• penetration through air and other materials
• deflection in an electric field.
structure
alpha particles consists of a helium nucleus, meaning it has 2 protons and 2 neutrons
a beta particle is an electron and comes from the nucleus
penetration
alpha particles have low penetrating ability and can only penetrate a few cm in air
they are absorbed by skin and paper
beta can penetrate several metre of air and can pass through a thin metal plate
beta can travel further than alpha particles in air
deflection
alpha and beta are deflected in opposite directions in an electric field
beta particles are deflected more than alpha particles
Explain what led to the plum pudding model of the atom being replaced by the nuclear model of the atom.
alpha particles scattering experiment
alpha particles directed at a gold foil
most alpha particles ass straight through so most of the atom is empty space
a few alpha particles deflected at large angles so mass is concentrated at the centre of the atom and the nucleus is positively charged
plum pudding model has mass spread throughout atom
plum pudding model has charge spread throughout the atom
Describe the process of nuclear fission inside a nuclear reactor.
a neutron is absorbed by a uranium nucleus
the nucleus splits into 2 parts
neutrons and gamma rays are emitted
Explain how the process of nuclear fusion leads to the release of energy.
lighter nuclei join to form heavier nuclei
some of the mass is converted to energy
Explain how the energy released by the chain reaction is affected by moving the control rods.
lowering the control rods increases the number of neutrons absorbed
therefore energy released decreases
The radioactive waste from a nuclear power station is buried underground.
People are warned to stay away from places where radioactive waste is buried.
Suggest one risk of going near the place where radioactive waste is buried.
irradiation
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