Posted in Physics Revision



Proton +1 1
Neutron 0 1
Electron -1 Almost 0

ATOM: made of a nucleus of protons and neutrons, with electrons orbiting.

ISOTOPE: an atom with the same number of protons and electrons and a different number of neutrons (same charge, different mass).

ION: an atom with the same number of protons and neutrons, but a different number of electrons (resulting a positive or negative charge).




This is a constant, low-level of radiation around us at all times.

Sources include:

  • CMBR (from space)
  • Elements such as radon gas
  • Rocks
  • Food
  • Nuclear tests eg nuclear bombs
  • Nuclear medicine



Radioactive sources can be dangerous because they are ionising – they can damage the body’s cells, which can lead to genetic mutations, causing diseases such as cancer.

Safety precautions that must be taken are:

  • Store radioactive sources in lead
  • Never touch a radioactive source.
  • Never point a radioactive source at anybody.
  • This symbol is the radiation warning symbol.



  • GM probe (part of a Geiger counter)
  • Spark counter
  • Cloud chamber

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