Key questions:
    What are isotopes?
    What are the types of isotopes?
    How do we measure isotopes?
    How do we express measurements of isotopes?
    What is isotope fractionation and how do we express it?
    What is equilibrium isotope fractionation?
    What is kinetic isotope fractionation?
    What is Raleigh distillation?
    What are some applications of stable isotopes?
  Isotopes of Elements
  Atomic Number = # Protons  = defines which element and its chemistry
  Atomic Weight =  protons + neutrons = referred to as isotopes
  Different elements have different numbers of neutrons and thus atomic 
  weights.  
  Example:  Carbon can exist as 12C, 13C, 14C
  How many protons and neutrons in each of the C isotopes?
      12C = 6P, 6N
      13C = 6P, 7N
      14C = 6P, 8N
      1 chemical, many isotopes!
  Where do Isotopes come from?
  In the beginning (Big Bang), light elements of H and He were 
  formed (and a little bit of Li)
  Nuclear reactions (ie: fusion) in stars created the remaining 
  elements (and are still creating), some of which have since 
  decayed to more stable elements
  There are 92 naturally occurring elements – some are stable, 
  some are not 
  Types of Isotopes
  Isotopes can be categorized into 2 categories:
  Stable isotopes – Isotopes that do not decay over the timescale of 
  earth history (4.5 billion years)
  Radioactive isotopes – Isotopes that spontaneously convert into 
  other nuclei at a discernable rate
       The chart of the nuclides (protons versus neutrons) 
       for elements 1 (Hydrogen) through 12 (Magnesium). 
                                             Valley of Stability
          Most elements have more 
          than one stable isotope.
                1:1 line                              b decay X
                                                             X
                                                       a decay
                                            Number of neutrons tends
                                            to be greater than the 
                                            number of protons