What are the different types of radioactive decay?

What is radio active decay?

Radioactive Decay:

  • A stable nucleus of an element has the correct balance of protons and neutrons.
  • Isotopes of an element which have too few or too many neutrons are usually unstable.
  • Carbon-12 is stable but carbon-14 which has 2 extra neutrons is unstable. Nitrogen-14 is stable but its isotope, nitrogen-13 which has 1 neutron less is unstable.
  • An unstable nucleus emits radiation in the form of an alpha particle, a beta particle or gamma rays to become a more stable nucleus.
  • Radioactive decay is the process in which an unstable nucleus changes into a more stable nucleus by emitting radiation.
  • In radioactive decay, the parent nuclide. emits radiation and changes into a daughter nuclide.
  • Radioactive decay is named after the type of radiation emitted.

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What are the different types of radioactive decay?

There are three types of radioactive decay:
(a) Alpha decay
(b) Beta decay
(c) Gamma decay

Alpha Decay

  1. In alpha decay, the unstable parent nuclide emits an alpha particle.
  2. Heavier unstable nuclei are more likely to undergo alpha decay. A bismuth-211 (83Bi211) nucleus is unstable and emits an alpha particle. Lawrencium-257 (103Lr257) also emits alpha particles.
  3. Figure shows a diagrammatic representation of the decay of bismuth-211.
    different types of radioactive decay 1
  4. The equation for the decay of bismuth-211 is as follows:
    different types of radioactive decay 2
  5. The daughter nuclide has 2 protons less and 2 neutrons less than the parent nuclide. This means that in alpha decay, the proton number is reduced by 2 while the nucleon number is reduced by 4.
  6. The general equation for alpha decay can be written as:
    different types of radioactive decay 3

Beta Decay

  1. In beta decay, the parent nuclide emits a beta particle.
  2. Usually heavier unstable nuclei with an excess of neutrons will undergo beta decay.
    (a) Carbon-12 is stable but a carbon-14 (6C14) nucleus is unstable and emits a beta particle.
    (b) Silicon-28 is stable but silicon-31 (14Si31) with three extra neutrons will emit a beta particle.
  3. During beta decay, one of the neutrons changes into a proton and an electron, as shown by the equation below.
    different types of radioactive decay 4The proton remains in the nucleus while the electron is emitted as a beta particle.
  4. This means that in beta decay, the nucleus loses a neutron but gains a proton.
  5. Figure shows a diagrammatic representation of the decay of silicon-31.
    different types of radioactive decay 5
  6. The equation for the decay of silicon-31 is as follows:
    different types of radioactive decay 6
  7. The proton number increases by one because of the new proton formed but the nucleon number is unchanged because of the loss of one neutron.
  8. The general equation for beta decay can be written as:
    different types of radioactive decay 7
  9. Other examples of nuclides which undergo beta decay are phosphorus-32, strontium-90, iodine-131 and actinium-228.

Gamma Decay

  1. In gamma decay, a nucleus in an excited state (higher energy state) emits a γ-ray photon to change to a lower energy
  2. state.
    There is no change in the proton number and nucleon number.
  3. A cobalt-60 nucleus in the excited state emits a y-ray photon. The equation for the decay is:
    different types of radioactive decay 8The (*) denotes the nucleus is in an excited state.
  4. The general equation for gamma decay can be written as:
    different types of radioactive decay 9
  5. The emission of γ-rays often accompany the emission of α-particles and β-particles. The following are some examples of these decays.

Radioactive Decay Series

different types of radioactive decay 10

  1. Sometimes the daughter nuclide of a radioactive decay is still unstable. It will eventually decay into another nuclide which is also unstable.
  2. This process continues as a radioactive decay series until a stable nuclide is reached. Each decay will emit either an a-particle or a β-particle and may be accompanied by γ-rays.
  3. Polonium-218 goes through a series of seven decays to become a stable lead-206 atom, as shown in Figure. Three a-particles and four β-particles are emitted in the process.
  4. If the initial and final nuclide of a decay series is given, the number of a-particles and β-particles emitted can be determined from the change in the nucleon number and proton number. The steps involved are:
    different types of radioactive decay 11
    Therefore, 6 alpha particles and 2 beta particles are emitted.
  5. A radioactive decay series can be shown on a graph of nucleon number against proton number. Figure shows part of a decay series.different types of radioactive decay 12different types of radioactive decay 13

Radioactive Decay Example Problems with Solutions

  1. State the type of decay and balance the equation.
    different types of radioactive decay 14
    Solution:
    different types of radioactive decay 15
  2. Nuclide 83Bi206 undergoes a series of decays to become 82Pb206. Determine the number of alpha particles and beta particles emitted in this decay series.
    Solution:
    different types of radioactive decay 16
    Therefore, 2 alpha particles and 3 beta perticles are emitted.