Nuclear Physics

 Radioactivity, Uses of Radioisotopes, Fission, Nuclear Waste

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  • Created by: tom
  • Created on: 14-04-11 12:10



  • Radioactivity is to do with unstable nuclei
  • The nucleus of a radioactive atom emits either an alpha (α) particle, beta (β) particle and/or gamma (γ) rays
  • An alpha particle is a slow-moving helium nucleus. It has a positive charge
  • A beta particle is a fast-moving electron. It has a negative charge
  • Gamma rays are short-wavelength electromagnetic waves. These have no charge and travel at the speed of light
  • The activity of a source is the average number of nuclei decaying per second
  • Activity is measured in Becquerel (Bq)
  • The activity of a radioactive substance decreases with time
  • Radioactivity is a random process because it is impossible to predict which nucleus will decay at a particular time
  • The half-life of a radioisotope is the average time taken for half the active nuclei to decay or disintegrate
  • The activity of a source is directly proportional to the number of active nuclei
  • The nucleus of an atom may be represented as      , where X is the chemical symbol, A is the nucleon or mass number and Z is the proton or atomic number
  • The protons and neutrons are also known as the nucleons
  • In alpha decay, the mass number decreases by 4, the proton number decreases by 2 and a new radioisotope is formed
  • In beta decay, the mass number remains the same, the proton number increases by 1 and a new radioisotope is formed
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Uses of Radioisotopes


  • Background radiation is always present and is due to radioactive substances in rocks, soil, air and cosmic rays
  • Sound background radiation comes from man-made sources
  • E.g. Nuclear and hospital waste
  • Radioisotopes are used as tracers in industry and hospitals
  • Gamma-emitting tracers are used to find leaks or blockages in underground pipes
  • Smoke detectors contain an alpha emitter
  • Carbon dating is used to date bone, cloth, wood and paper. It relies on the radioactivity isotope of carbon-14
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Nuclear Fission


  • Nuclear power stations use uranium as a fuel. Most of the waste is radioactive for thousands of years
  • Reactions produce the heat to produce steam to turn the turbines, which turn the generators to produce electricity
  • In a fission reaction, a neutron is captured by a uranium-235 nucleus and splits into two smaller (daughter) nuclei and either two or three neutrons
  • Energy is released when a uranium nucleus splits
  • Materials become radioactive when they capture neutrons in a nuclear reactor
  • In a chain reaction, the neutrons can cause further fission reactions
  • One destructive use of fission is the atomic bomb. One peaceful use if electricity production
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The Process of Nuclear Fission


  • In the process of the fission of uranium-235:
  • A uranium-235 absorbs a neutron, making it unstable
  • It splits into two daughter nuclei, which are also unstable, and two or three spare neutrons
  • The fission products have a lot of kinetic energy, which is removed by a coolant
  • The coolant generates steam that turns a turbine
  • The spare neutrons can cause further fission of other nuclei in a chain reaction
  • If each spare neutron were allowed to cause another fission, the result would be a chain reaction which would be out of control. To maintain the reaction at a steady rate, on average just one of the neutrons released by each fission is allowed to go on and cause further fission
  • In the core of a nuclear reactor, control rods absorb the spare neutrons to control the rate of reaction. It is also a safety feature
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Nuclear Waste


  • Nuclear power has one major disadvantage which is how to dispose of the nuclear waste. There are three main categories:
  • Low-level waste such as laboratory clothing and packaging materials; these are either buried either underground or at sea
  • Intermediate-level waste such as the casing used for nuclear fuel and reactor parts that have been replaced; these are kept in stores with thick concrete walls or buried in deep trenches with concrete linings
  • High-level waste such as spent fuel rods; these present a long-term disposal problem since they remain significantly radioactive for thousand of years; much of this waste is in temporary storage in tank of water until the problem of what to do with it can be solved
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