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(c) doc b(c) doc bDoc Brown's Chemistry KS4 science GCSE/IGCSE/AS Physics Revision Notes

7a. What happens in alpha & beta radioactive decay?

& 7b. Production of radioisotopes - artificial sources

In terms of radioactive sources (radioisotopes, radionuclides) what is alpha decay? and what is beta decay? What happens in the nucleus of unstable radioactive atoms? How do we write nuclear equations to represent these nuclear changes? Why is gamma radiation emitted from atomic nuclei? What is a positron? What is positron emission? How do we make artificial (man-made) radioisotopes? Neutron bombardment!

Radioactivity & nuclear physics Index 1a. The Structure of Atoms - 3 fundamental particles * 1b. What it is an atom like? * 2a. What is Radioactivity? Why does it happen? * 2b. How did they find out there were three types of atomic-ionising radiation? * 3a. Detection of Radioactivity and its measurement, units * 3b. Ionising Radiation sources * 4a. The properties of the three types of radioactive emission and symbols * 4b The dangers of radioactive emissions - beware of ionising radiation from radio-isotopes! * 5. The uses of radioactive Isotopes emitting alpha, beta or gamma radiation * 6a. The half-life of a radioisotope - how long does material remain radioactive? implications! * 6b. Uses of decay data and half-life values * 7a. What actually happens to the nucleus in alpha and beta radioactive decay? nuclear equations * 7b. The production of Radioisotopes - artificial sources * 8. Nuclear fusion reactions and the formation of 'heavy elements' * 9. Nuclear Fission Reactions, nuclear power energy resource

 

(c) doc b7a. What happens overall in Alpha and Beta Radioactive Decay?

  • (c) doc b Alpha Decay e.g. the nuclear equation

    • (c) doc b 

    • A helium nucleus, the alpha particle, of 2 protons and 2 neutrons is emitted at high speed/kinetic energy from the nucleus.

    • The residual atom (sometimes referred to as the politically incorrect 'daughter nuclide'!*) has a mass number of 4 less, and an atomic number of 2 less, than the 'parent' or original atom.

    • Most atoms with an atomic number of over 82 (Pb) usually undergo alpha decay.

    • * Sadly, apart from Marie Curie and her daughter, in the late 19thC/early 20thC, nuclear physics was dominated by male scientists!

    • more on properties of alpha particles & uses of alpha radiation
  • (c) doc b- Beta- Decay e.g. the nuclear equation

    • (c) doc b  

    • A neutron in the nucleus changes spontaneously into a proton and a high kinetic energy electron forms the emitted beta particle.

    • Since the proton and neutron have a mass of 1 and the electrons mass is negligible, the mass number stays the same but the atomic (proton) number rises by 1.

    • This tends to happen with isotopes with too many neutrons to be stable (too high an n/p ratio) and lies above the stability curve shown above.

    • By changing a neutron to a proton the n/p ratio is reduced to the nucleus of an isotope lying in the stability band.

    • (c) doc b Balancing: The changes can be represented as nuclear equations and they must balance in mass number and nuclear or emitted particle charge (protons in alpha decay, protons and electrons in beta decay).

    • In (1) mass = 235 = 231 + 4 and protons = 92 = 90 + 2.

    • For (2) mass = 14 = 14 + 0 and for protons/beta charge = 6 = 7 + (-1).  In either case a new element is formed i.e. the 'transmutation' of one element to another has happened. It also means that there can never be a 'pure' Radioisotope.

  • (c) doc b Gamma emission: The emission of gamma radiation from a nucleus does not involve any change in the atomic (proton) number or mass number.

  • Positron emission is required by some syllabuses

    • (c) doc b+ Positron emission (beta+ decay)

    • e.g. (c) doc b

    • A proton changes to neutron  and  a 'positive electron' called a positron is expelled with very high kinetic energy. A positron has the same mass as an electron but carries a positive charge (it is the 'anti-matter' particle of the electron!).

    • Since the proton and neutron have a mass of 1 and the electrons mass is negligible, the mass number stays the same but the atomic (proton) number falls by 1.

    • This tends to happen with isotopes with too few neutrons to be stable (too low an n/p ratio) and lies below the stability curve shown in a previous graph. By changing a proton to a neutron the n/p ratio is increased to an isotope lying in the stability band.

Advanced Chemistry Page Index and Links

7b. The production of radioisotopes - artificial sources

  • Neutron bombardment is used to make artificial or man-made radioisotopes.

  • To meet the industrial and medical demand for Radioisotopes (as described earlier) many are made by allowing stable isotopes to be hit by neutrons in a small research scale nuclear reactor.

  • Note again, the balancing of nuclear equations e.g.

(c) doc b

to make carbon-13, used as a chemical tracer carbon in studying the mechanisms or organic chemistry reactions

(c) doc b

to make sodium-24, which can be used in tracer studies of animal blood circulation

(c) doc b

to make cobalt-60, used as the gamma source for cancer radiotherapy.

Advanced Chemistry Page Index and Links

(c) doc b(c) doc bRADIOACTIVITY multiple choice QUIZZES and WORKSHEETS

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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