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2a. What is Radioactivity? What causes it?

2b. How did they find out there are three types of ionising radiation? Effects of electric and magnetic fields

Doc Brown's Chemistry

KS4 science GCSE Physics Revision Notes

What to mean by the term 'radioactive' material? Why are some atoms radioactive and others not? What are the types of radioactive emissions? Why are they called ionizing radiations? How can we show by experiment that there are three types of atomic nuclear radiation? These revision notes on what radioactivity is and should help with GCSE/IGCSE physics courses and A/AS level physics courses


See also Electromagnetic radiation, types, properties, uses and dangers gcse physics revision notes

(c) doc b2a. What is Radioactivity? and why does it happen?

  • The nucleus is composed of protons and neutrons and glued together by a strong attraction BUT only certain combinations of the n/p ratio seem to be stable (see stability curve graph on right). Any isotope of any element that does not lie in the stability band with a stable n/p ratio is likely to be radioactive!
  • Radioactivity results from the random and spontaneous breakdown of the unstable nucleus of an atom.
  • This breakdown is called radioactive decay (nuclear decay) of the unstable nucleus of the atom (radioisotope).
  • In the breakdown of the unstable nucleus, energy is released by the emission (usually) of three types of ionising radiation (nuclear radiation) called  alpha particle radiation, beta particle radiation and gamma ionising radiation (see diagram below).
  • When an unstable nucleus splits a different nucleus with a different number of protons is formed, as well as the emission of radiation, and so a different element is formed (NOT possible in chemical changes, but this is a nuclear reaction!).
  • The breakdown of an unstable atom is referred to as radioactive decay or radioactive disintegration.
    • It is a totally random process meaning it is a matter of chance which particular nucleus decays.

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2b. How did they find out there were three types of atomic ionising radiation?

The basic experimental technique for separating beams of a mixture of particles

  • (c) doc bA radium source was used, which also contains other radio-isotopes, and a lead casing was the only safety precaution used!
    • How people like Marie Curie and Ernest Rutherford etc. survived beyond the age of 60 is a mystery!
  • Anyway! it was found that the original 'emission' from the radioactive radium source was split into three beams by an electric or magnetic field (diagram on the right).
    • (i) The alpha beam was attracted/deflected towards a negative plate, showing it was positive, since opposite charges attract/like charges repel - the rules of electric charge interaction.
    • (ii) The beta (negative electrons) beam bent towards a positive plate (showing it was negative).
    • (iii) The gamma beam passed through un-deflected (showing it had no charge).
  • Note: Although the alpha particles have the biggest charge of +2, the beta beam (smaller charge of -1) is more easily deflected because of its much smaller mass (nearly 8000 x smaller, mass ratio for He2+ : e- is 4 : 1/1850).
  • Note that in other nuclear particle separation experiments, a proton (+), or any other positive particle beam, bends towards the negative plate.
  • Other experiments have detected positron (positive electron) emission from beta plus radioactive decay.



1. Atomic structure, fundamental particles and radioactivity

2. What is radioactivity? Why does it happen? What radiations are emitted?

3. Detection of radioactivity, measurement, dose units, ionising radiation sources, background radiation

4. The properties and dangers of alpha, beta & gamma radioactive emission

 5. The uses of radioactive Isotopes emitting alpha, beta or gamma radiation

6. Half–life of radioisotopes, how long does material remain radioactive? Uses of decay data & half–life values

7. Nucleus changes in radioactive decay? how to write nuclear equations? Production of Radioisotopes

 8. Nuclear fusion reactions and the formation of 'heavy elements'

 9. Nuclear Fission Reactions, nuclear power energy resources

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Easier-Foundation Radioactivity Quiz

or Harder-Higher Radioactivity Quiz

 (c) doc b five word-fills on radioactivity * Q2 * Q3 * Q4 * Q5and ANSWERS!

crossword puzzle on radioactivity and ANSWERS!

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