Radioactivity (6.18-6.27)

Decay equations and half lifes

Follows specifications points

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Beta minus decay (6.18)

  • A neutron can change into a proton and an electron.
  • When this happens the proton stays in the nucleus (changing the element as there is now one more proton in the nucleus) and the electron (the 'beta minus') is emitted from the nucleus.
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Beta plus decay (6.19)

  •  A proton can change into a neutron and a positron.
  • When this happens, the nutrons stays in the nucleus (changing the element as there is now one less proton in the nucleus) and the positron (the 'beta positive') is emitted form the nucleus.
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Alpha decay (6.20) → effects on A no. + M no.

Effects on the atomic number and mass number of radioactive decays

  • an emission of an alpha particle causes the mass number of the nucleus to decrease by 4 and the atomic number to decrease by 2

so thats...

  • mass no. = -4
  • atomic no. = -2

An apha particle is identical to a helium nucleus; it contains 2 protons and 2 nutrons.

zXaz-2Ya-4 + 2He4

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Beta minus decay (6.20) → effects on A no. + M no.

Effects on the atomic number and mass number of radioactive decays

  • An emission of a beta minus particle causes the mass number to stay the same and the atomic number to increase by one

6C147N14+ -1Beta0

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Beta plus decay (6.20) → effects on A no. + M no.

Effects on atomic number and mass number of radioactive decay

  • Emission of a beta plus particle causes mass number to stay the same and the atomic number to decrease by one

6C115B11++1 Beta0

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Gamma decay (6.20) → effects on A no. + M no.

Effects on atomic number and mass number of radioactive decay

  • gamma radiation changes neither the atomic or mass number

0Gamma0

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Neutron emission (6.20) → effects on A no. + M no.

Effects on atomic number and mass number of radioactive decay

  • neutron emisson causes the mass number of the nucleus to decrease by one and the atomic number stays the same

4B94B8+ neutron

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Radioactive decay energy loss (6.21)

  • After emitting an alpha or beta particle, the nucleus will often still have excess energy and will emit it in the form of a gamma ray
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Balancing nuclear equations (6.22)

https://www.bbc.co.uk/bitesize/guides/zq3d6yc/revision/4

consolidate with practice questions

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Activity of radioactive source (6.23)

  • activity of radioaactive isotope is number of nuclear decays per second
  • this decreases over time
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Unit of activity (6.24)

  • 1 bq (Becquerel) is one nuclear decay per second
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Half-life definition (6.25)

  • half-life of a radioactive isotope is the time taken for the activity of the source to decay by half
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Random nucleus decay (6.26)

  • it is not possible to predict when particular nucleus will decay, but as there are billions f them it is possible to say that a certain amount will decay by a certain time.
  • in each half-life the activity, the number of undecayed nuclei or the count rate will drop to half of what it was.
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Calculate using half-life and graphs (6.27)

For example the amount of a sample remaining after four half-lives could be expressed as:

  • -a fraction - a ½ of a ½ of a ½ of a ½ remains which is ½ x ½ x ½ x ½ = 1/16 of the original sample
  • -a decimal - 1/16 = 0.0625 of the original sample
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