Radioactivity
(Exponential
Example)
Atoms
Atoms are made of protons, electrons and
neutrons.
Protons and neutrons
reside in the middle, or
nucleus, and electrons
reside in the outer
portion of an atom.
Atomic Number
The atomic number is the number of protons an
element has.
Hydrogen has one proton so its atomic number is
1 (see picture).
Uranium has 92 protons so its
atomic number is 92.
Atomic Mass Number
The atomic mass number indicates the total number
of protons and neutrons in the nucleus
For example, carbon has 6 protons so its atomic
number is 6. Its atomic mass number, however,
depends on the number of protons and neutrons
it has. Carbon typically has an atomic mass
number of 12. (6 protons + 6 neutrons = 12)
Atoms can have isotopes or variations in their
Atomic Mass Number.
For example, carbon-14 is an isotope of carbon.
Carbon-14 still has 6 protons but the 14 indicates
its Atomic Mass
Number is 14
(6 protons + 8 neutrons = 14)
Radioactive Decay / Half life
Atoms like carbon-14, don’t remain carbon-14
forever. They can change or decay into other
isotopes or different elements naturally.
We measure a thing called half life, which is the
time it takes for half of a sample of atoms to
decay or change into something else.
Half life example
Suppose we find a rock with a
C-14
mass of 100 grams that is entirely
carbon-14
Carbon-14 decays to nitrogen-14 with a half life of
5730 years
So after 5730 years our rock
will contain 50 grams of
carbon-14 and 50 grams of
C-14
N-14
nitrogen-14
After an additional 5730 years we’ll have 25 grams
of carbon 14 and 75 grams of nitrogen-14 as
half of our carbon-14 again decays
C-14
N-14
Half life example
If we found a rock that was 50% carbon-14 and
50% nitrogen-14, we can assume that it is 5730
years old. This assumes nothing has happened
to the rock that would change this decay rate –
(erosion, use by animals etc.)
Since the atoms decay at a fixed percent rate this
naturally lends itself to exponential problems.