• Elements undergo chemical changes so it can become more stable.

• Stability depends on the proton to neutron ratio.

  • Atomic numbers < 20 are the most stable because the ratio is about 1:1

• Henri Becquerel called emission from decay uranic rays because they were emitted from uranium.

• Marie Curie discovered Po (Polonium) and Ra (Radon) which emitted uranic rays, changing uranic rays to radioactivity.

Radioactivity: emission of subatomic particles or high energy electromagnetic radiation by nuclei. such atoms/isotopes said to be radioactive

Nuclear Decay:

• protonsnucleons, (neutrons + protons)X

• An unstable nucleus undergoes a change and reduction in energy to become more stable.

• The four types of nuclear decay (+ gamma)

  • Alpha decay

    • largest ionizing power, lowest penetrating power

    • can penetrate matter

    • nucleus emits alpha particle

    • # nucleons must =, # protons must =

    • 24He is the alpha particle. It is always one of the daughter particles.

  • Beta decay

    • high speed electron is ejected from a nucleus

    • turns neutron into proton

    • it has a lower ionizing power than alpha particle but a higher penetration power

  • Positron emission

    • positron is antiparticle of e

    • collision with e causes gamma ray emission

    • cause: too little neutrons

    • proton converted into neutron, emits positron

  • Gamma decay

    • electromagnetic radiation

    • high-energy photons

    • no charge, no mass

    • usually emitted in conjunction with other radiation types

    • lowest ionizing power, highest penetrating power

    • requires several inches lead shielding

  • Electron capture

    • particle absorbed by unstable nucleus

    • converts proton into neutron

    • different from beta decay! 2 reactants, 1 product

• Nuclear decay series:

  • Uranium has an atomic number greater than 83. Therefore it is naturally radioactive.

  • Uranium decays into Thorium by alpha decay.

  • Thorium decays into Protactinium by alpha decay.

  • Protactinium decay next and so on until we reach a stable non-reactive element.

Nuclear half-life:

• Unstable nuclei emit either an alpha, beta, or positron particle to try to shed mass or improve their neutron to proton ratio.

• You cannot predict when an oculus will disintegrate for individual nuclei, but you can when you look at large # of atoms.

• The half-life of any nuclide does not depend on temperature, pressure, or amount of material left. It depends on the N/P ratio.

• Loss of mass to decay

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