Background radiation and its sources, medical uses of radiation, and how nuclear fission and fusion release energy. Physics only content.
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1.What is background radiation?
The low level radiation that is around us all the time, from natural and man-made sources.
2.Name four natural sources of background radiation.
Rocks such as granite which release radon gas, cosmic rays from space, food and drink, and the air.
3.Name two man-made sources of background radiation.
Medical procedures such as X-rays, and waste from the nuclear industry.
4.Why does background radiation vary between locations?
The underlying rock differs, so places built on granite have higher radon levels than others.
5.Why must background radiation be measured before an experiment?
So it can be subtracted from readings, leaving only the count rate from the source itself.
6.What is radiation dose measured in?
Sieverts, or millisieverts.
7.What does radiation dose measure?
The risk of harm from exposure, taking into account the amount of radiation and how damaging that type is.
8.Give a medical use of radioactive sources for diagnosis.
A tracer is injected or swallowed, and its progress is followed with an external detector to check how an organ is working.
9.What properties should a medical tracer have?
A short half-life and gamma emission, so it leaves the body quickly and can be detected from outside.
10.Give a medical use for treatment.
Targeted gamma radiation is used to destroy cancer cells.
11.Why must the risks of medical radiation be weighed against benefits?
Radiation itself can cause cancer, so it is only used when the benefit to the patient clearly outweighs that risk.
12.What is nuclear fission?
The splitting of a large unstable nucleus into two smaller nuclei of roughly equal size.
13.How is fission usually triggered?
The unstable nucleus absorbs a neutron, which makes it split.
14.What is produced by fission?
Two daughter nuclei, two or three neutrons, and energy carried by the products as kinetic energy, plus gamma radiation.
15.What is a chain reaction?
The neutrons released by one fission go on to cause further fissions, which release more neutrons, and so on.
16.How is a chain reaction controlled in a reactor?
Control rods absorb some of the neutrons, so that on average only one neutron from each fission causes another.
17.What happens if a chain reaction is uncontrolled?
The rate of fission increases rapidly, releasing an enormous amount of energy, which is what happens in a nuclear weapon.
18.What is nuclear fusion?
Two light nuclei joining together to form a heavier nucleus.
19.What happens to mass during fusion?
Some of the mass is converted into energy, released as radiation.
20.Why does fusion require extreme conditions?
Both nuclei are positively charged and repel strongly, so very high temperatures and pressures are needed to force them close enough to join.
21.Where does fusion happen naturally?
In stars, including the Sun.
22.Give an advantage of fusion over fission.
The fuel is far more abundant and it produces much less radioactive waste.
23.Why is fusion not yet used to generate electricity?
The conditions needed are so extreme that no reactor has yet produced more energy than it consumes over a sustained period.
24.Compare fission and fusion in one sentence.
Fission splits a large nucleus into smaller ones, whereas fusion joins small nuclei into a larger one. Both release energy.
25.Which nucleus is commonly used as fission fuel?
Uranium-235, and also plutonium-239.
26.Why is nuclear waste a long term problem?
Some products remain radioactive for thousands of years, so they must be stored securely for a very long time.
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