What you should know about atomic structure and radioactivity from GCSE

P2.5 What happens when radioactive substances decay, and the uses and dangers of their emissions

Radioactive substances emit radiation from the nuclei of their atoms all the time. These nuclear radiations can be very useful but may also be very dangerous. It is important to understand the properties of different types of nuclear radiation. To understand what happens to radioactive substances when they decay we need to understand the structure of the atoms from which they are made. The use of radioactive sources depends on their penetrating power and half-life.

Candidates should use their skills, knowledge and understanding to:

  • evaluate the effect of occupation and/or location on the level of background radiation and radiation dose
  • evaluate the possible hazards associated with the use of different types of nuclear radiation
  • evaluate measures that can be taken to reduce exposure to nuclear radiations
  • 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
  • explain how results from the Rutherford and Marsden scattering experiments led to the 'plum pudding' model being replaced by the nuclear model.

Additional guidance:

Candidates should realise that new evidence can cause a theory to be re-evaluated.

Candidates should realise that, according to the nuclear model, most of the atom is empty space.

P2.5.1 Atomic structure

a) The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded by electrons.

Additional guidance:

Candidates should appreciate the relative size of the nucleus compared to the size of the atom.

b) The relative masses and relative electric charges of protons, neutrons and electrons.

c) In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no overall electrical charge.

d) Atoms may lose or gain electrons to form charged particles called ions.

e) The atoms of an element always have the same number of protons, but have a different number of neutrons for each isotope. The total number of protons in an atom is called its atomic number. The total number of protons and neutrons in an atom is called its mass number.

P2.5.2 Atoms and radiation

a) 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.

Additional guidance:

Candidates should be aware of the random nature of radioactive decay.

b) The origins of background radiation.

Additional guidance:

Knowledge and understanding should include both natural sources, such as rocks and cosmic rays from space, and man-made sources such as the fallout from nuclear weapons tests and nuclear accidents.

c) Identification of an alpha particle as two neutrons and two protons, the same as a helium nucleus, a beta particle as an electron from the nucleus and gamma radiation as electromagnetic radiation.

d) Nuclear equations to show single alpha and beta decay.

e) Properties of the alpha, beta and gamma radiations limited to their relative ionising power, their penetration through materials and their range in air.

f) Alpha and beta radiations are deflected by both electric and magnetic fields but gamma radiation is not.

g) The uses of and the dangers associated with each type of nuclear radiation.

h) The half-life of a radioactive isotope is the average 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.