2a. What is Radioactivity? and why does it happen?

• The nucleus is composed of protons and neutrons and glued together by a strong nuclear attractive forces BUT only certain combinations of the neutron/proton (n/p) ratio in the nucleus seem to be more stable than others (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 more 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-isotope (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 radiation (see diagram below).
  • These emissions are ALL high velocity and high energy particles or radiation.
  • Alpha particles are positive (2+), mass 4, 2 protons (+) combined with 2 neutrons (0).
    • The expelled alpha particle is the equivalent of the nucleus of a helium atom (which is what it is!)
    • 
    • alpha particle emission on left
    • more on properties of alpha particles & uses of alpha radiation & alpha decay nuclear equations
  • Beta particles are negative, mass 1/1850, a negative electron (charge -, minus), ⁰_-1e.
    • The expelled beta minus particle from the unstable nucleus is a high speed electron.
      • (you should state that this electron is a beta minus, because there is beta plus particle called a positron!
    • 
    • beta particle emission on right
    • more on properties of beta particles & uses of beta radiation & beta decay nuclear equations
  • Gamma photon, mass 0 (~zero), radiation is electrically neutral (charge 0 or zero)
    • Gamma radiation emission often accompanies alpha and beta particle emission - its a way that a newly formed and temporarily unstable nucleus gets rid of its excess energy to become more stable.
    • 
    • gamma photon emission at the bottom
    • more on the properties of gamma photons and uses of gamma radiation
• 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.

• For more details about radiations, see detailed table of information in 4a. on the three types of radioactive emission, alpha, beta and gamma ionising radiations.

• Because it involves high energy nuclear changes, radioactivity is completely unaffected by the temperature, pressure, physical state or chemical state of the atoms.
  • You cannot alter the rate of decay at all!
  • The energy changes involved with nuclear changes like radioactivity, are much greater, than those for physical or chemical changes of materials like boiling or fuel combustion etc.
    • I've some calculations in section 4. to prove this point (but NOT required by GCSE students!).

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

Basic experimental technique for separating beams of a mixture of particles

• A 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.

TOP OF PAGE

Atomic structure, history, definitions, examples and explanations including isotopes gcse chemistry notes

1. Atomic structure and fundamental particle knowledge needed to understand radioactivity gcse physics revision

2. What is Radioactivity? Why does it happen? Three types of atomic-nuclear-ionising radiation gcse physics notes

3. Detection of radioactivity, its measurement and radiation dose units, ionising radiation sources - radioactive materials, background radiation gcse physics revision notes

4. Alpha, beta & gamma radiation - properties of 3 types of radioactive nuclear emission & symbols ,dangers of radioactive emissions - health and safety issues and ionising radiation gcse physics revision

5. Uses of radioactive isotopes emitting alpha, beta (+/–) or gamma radiation in industry and medicine gcse notes

6. The half-life of a radioisotope - how long does material remain radioactive? implications!, uses of decay data and half-life values - archaeological radiocarbon dating, dating ancient rocks gcse physics revision

7. What actually happens to the nucleus in alpha and beta radioactive decay and why? nuclear equations!, the production of radioisotopes - artificial sources of radioactive-isotopes, cyclotron gcse physics revision notes

8. Nuclear fusion reactions and the formation of 'heavy elements' by bombardment techniques gcse physics notes

9. Nuclear Fission Reactions, nuclear power as an energy resource gcse physics revision notes

Easier Foundation Tier Radioactivity multiple choice QUIZ

Harder Higher Tier Radioactivity multiple choice QUIZ

Worksheet QUIZ Question 1 on RADIOACTIVITY - absorption of alpha, beta and gamma radiation

Worksheet QUIZ Question 2 on RADIOACTIVITY - dangers & monitoring ionising radiation levels

Worksheet QUIZ Question 3 on RADIOACTIVITY - revision of atomic structure

Worksheet QUIZ Question 4 on RADIOACTIVITY - what happens to atoms in radioactive decay?

Worksheet QUIZ Question 5 on RADIOACTIVITY - uses of radioisotope and half-life data

ANSWERS to the WORD-FILL WORKSHEET QUIZZES

Crossword puzzle on radioactivity and ANSWERS!

[SEARCH BOX]

TOP OF PAGE

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

 Doc Brown's Chemistry 

*