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Radioactivity

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Radiation

  • Energy transmitted by waves or particles
  • Sources:
    • Thermal E (you already know this one)
    • e- movement within atom
      • Releases X-rays and photons of light
    • Nuclear Decay
      • Releases alpha particles, beta particles, and gamma rays

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Nuclear Decay

  • Occurs when a nucleus is unstable
    • Balance between forces in a stable nucleus holds it together
      • Strong force attracts p+ and n0
      • Electrical force repels p+
      • Typical stable nucleus has slightly more n0 than p+
      • An unstable nucleus will decay to become stable

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α (alpha) decay

  • Nucleus emits one α particle:
    • 2 protons and 2 neutrons

BIG particle

lots of damage, but non-penetrating

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Radon – an alpha emitter

  • Alpha particles outside your body are of little threat – they hit dead skin
  • Alpha particles emitted inside your body can ionize DNA in your cells
    • (ion – charged particle)
  • Radon gas is an alpha emitter; if you spend time in a basement you should test for it to avoid higher cancer risk.

$15 – airchek.com

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β (beta) decay

  • One neutron converts to a proton and an electron in Beta Decay.
    • Proton stays in nucleus, electron shoots out
    • The ejected electron is called a beta particle.

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    • (technically there are two types of Beta decay; beta+ and beta–)
    • Beta– emits a positron = an antimatter particle that’s opposite an electron

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Elements and Isotopes

  • Element type determined by # of p+
    • (label box on periodic table)
  • Atomic # = p+
  • Mass # = p+ + n0 (average)
    • Why is this an average?
      • Protons for an element will not vary
      • Neutrons may exist in different numbers
      • Isotopes – atoms of same element with different n0

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γ (gamma) radiation

  • Short-wavelength electromagnetic wave released when a nucleus decays is in the form of gamma radiation.
    • No mass, no charge
    • Very penetrating
    • Often associated with alpha and beta decay

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Isotope examples:

  • What is Carbon – 12?
    • Carbon with 6 p+ and 6 n0

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  • What is Carbon – 14?

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Practice

  • What happens to C – 14 if it could undergo α (alpha) decay?
    • First count protons and neutrons, then subtract an α particle.
  • What element does it turn into?

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  • Now try Oxygen-17!

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Practice 2

  • What happens to C-14 if it undergoes β decay?
    • First count protons and neutrons, then convert a neutron to a proton.

(a β particle, or e-, will be ejected as well, but doesn’t affect the answer)

  • What element does it turn into?

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  • Now try Iodine – 127!

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Time for nuclear decay

  • Nuclear decay results in radioactive atoms being changed to other forms.
    • This process happens at different rates (half-lives)
    • Atoms decay until none of the “parent” nuclei are left; all have decayed into “daughters”

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Half Life

  • time it takes for ½ of a quantity to decay.
    • Something with a short half life releases lots of radiation quickly, but is gone quickly as well.

After four half lives, a substance will be:

½…. ¼…. 1/8…. 1/16 parent nuclei

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