Critical mass

• Resources Structure
• Key Stage 4
• Physics
• XVIII. Nuclear physics
• 103. Nuclear fission

• Exam Specifications
• Key Stage 4
• AQA GCSE Science A (4461) Physics
• II. Physics 1b - Radiation and the Universe
• 2. What are the uses and dangers of emissions from radioactive substances?
• to evaluate the possible hazards associated with the use of different types of nuclear radiation
• to evaluate measures that can be taken to reduce exposure to nuclear radiations
• to evaluate the appropriateness of radioactive sources for particular uses, including as tracers, in terms of the type(s) of radiation emitted and their half-lives.
• The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded by electrons.
• The atoms of an element always have the same number of protons, but have a different number of neutrons for each isotope.
• Some substances give out radiation from the nuclei of their atoms all the time, whatever is done to them. These substances are said to be radioactive.
• Identification of an alpha particle as a helium nucleus, a beta particle as an electron from the nucleus and gamma radiation as electromagnetic radiation.
• Properties of the alpha, beta and gamma radiations limited to their relative ionising power, their penetration through materials and their range in air.
• Alpha and beta radiations are deflected by both electric and magnetic fields but gamma radiation is not.
• The uses of and the dangers associated with each type of nuclear radiation.
• The half-life of a radioactive isotope is defined as the time it takes for the number of nuclei of the isotope in a sample to halve or the time it takes for the count rate from a sample containing the isotope to fall to half its initial level.
• AQA GCSE Physics (4451)
• IV. Physics 1b
• 15. What are the uses and dangers of emissions from radioactive substances?
• The uses of and the dangers associated with each type of nuclear radiation.
• V. Physics 2
• 26. What are nuclear fission and nuclear fusion?
• to sketch a labelled diagram to illustrate how a chain reaction may occur.
• There are two fissionable substances in common use in nuclear reactors, uranium 235 and plutonium 239.
• Nuclear fission is the splitting of an atomic nucleus.
• For fission to occur the uranium 235 or plutonium 239 nucleus must first absorb a neutron
• The nucleus undergoing fission splits into two smaller nuclei and 2 or 3 neutrons and energy is released.
• The neutrons may go on to start a chain reaction.
• Nuclear fusion is the joining of two atomic nuclei to form a larger one.
• Nuclear fusion is the process by which energy is released in stars.
• AQA GCSE Physics (4451)
• I. Physics 2
• 10. What are nuclear fission and nuclear fusion?
• Nuclear fission is the splitting of an atomic nucleus.
• For fission to occur the uranium 235 or plutonium 239 nucleus must first absorb a neutron
• The nucleus undergoing fission splits into two smaller nuclei and 2 or 3 neutrons and energy is released.
• The neutrons may go on to start a chain reaction.
• Nuclear fusion is the joining of two atomic nuclei to form a larger one
• Nuclear fusion is the process by which energy is released in stars.
• to sketch a labelled diagram to illustrate how a chain reaction may occur.
• There are two fissionable substances in common use in nuclear reactors, uranium 235 and plutonium 239.

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