Radiometric Dating
1. Matter - Composed of Atoms; Molecules are formed with atoms - often arranged in crystals
  1. Atom Nucleus = Protons (P) (positive charged); Neutrons (N) (neutral - essentially a proton + electron).
  2. Henry Faul - Nucleus are so dense that an imaginary nucleus of 1 inch in diameter would weigh more than 10 cubic miles of rock.
  3. Electrons (E) - Orbit nucleus at high speed.
2. Designations:
  1. Atomic Mass - Given in neutron weight - determines chemical activity.
  2. Atomic Number - Number of protons; i.e. 2HE4
  3. Nuclide - Given species of atom

    1) Nuclides with same mass but different atomic number = Isobars

    2) Nuclides with same number of protons but different number of neutrons = Isotopes (chemically alike but physically different) - unstable.

3. Radioactive Decay: Parent => Daughter Element
  1. Alpha-Decay (a): Isotope loses 2 protons and 2 neutrons (a helium nucleus), so helium is released with a-decay. e.g. 238U +> 234TH (238U = 92P + 146N;234TH = 90P + 144N)
  2. Beta-Decay (b): Isotope loses a neutron and gains a proton: b = e, so n +> P+E, or 
    N => P + b. E.g. 87RB => b + 87 SR (87RB = 37P + 50 N. 87SR = 38P + 49N)
  3. Electron-Capture (e): Electron from inner orbit moves into nucleus. Since no electrons are free in the nucleus. Net is +1N (e + P = N). E.g. 40K => 40AR (40K = 19P + 21N. 40AR = 18P + 22N)
  4. Decay is random and occurs in proportion to the amount of Isotopes present. Therefore, as it decays, the amount decaying over time decreases. This is called Exponential decay and is measured in Half-Lives (T½).
E. Decay Rates
Half-Life
Type of Decay
Daughter
40K 1.3 * 109 Electron Capture 40AR
87RB 4.7 * 1010 Beta 87SR
238U 4.5 * 109 8 Alpha + 6 Beta 206PB
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