Radiocarbon dating determines the age of organic
matter such as dinosaur bones. Radiocarbon dating
was discovered in 1947 by a chemist, Willard Libby.
By measuring the amount of the radioactive isotope,
such as carbon 14, that is left in an organism one
can determine an approximate age of an organism
(since death). To approximate how many years
earlier an organism died one can apply the
exponential decay formula. This formula is
discussed later in this paper.
Carbon 14 is an isotope. An isotope is an
element with a different amount of neutrons than protons. There are
multiple isotopes that are useful. An isotope of
Iodine can be injected into the body and will show
up on x-rays. This way doctors can look at your
circulatory system.
The atom, carbon 14, is radioactive. Please
note that the radioactivity is minor and isn’t
close to what we associate with radioactivity. A
half-life is the time necessary for one half of a
radioactive material to decay. This is used to
date the amount because one half of the radioactive
material is decayed it takes another half-life for
one half of the remaining material to decayÖ The
approximate half-life of carbon 14 is 5730 +- 30 years (5730 plus or minus 30 years).
(for decay formulas 5730 will be the number used).
One might ask: Is Carbon 14 ever completely
dispersed? The answer is yes. As the amount left
approaches 0 it gets so small it is immeasurable.
And the measurement--if one obtains a
measurement--isn’t very exact.
Since carbon 14 is only good for dating up to
about 23,000 years, then how do people date things
back billions of years old? For example, the age
of the earth is approximated at 4.5 billion years.
The answer is that there are other isotopes that
decay much, much slower which can be used.
Many people debate the accuracy of radiocarbon
dating. The debate is mainly due to religious
views. However most bad results come from improper
techniques and not the inaccuracy of radiocarbon
dating.
The process of radiocarbon dating can be
disrupted by neutrino bombardment and argon gas.
Neutrino bombardment is theoretical, but basically
it speeds up the decay of an isotope. Argon gas
will reset the clock of an isotope. In other
words, argon gas makes it appear as though no decay
has occurred.

How Carbon 14 is created :
The creation of Carbon 14 seems very
complicated, but actually is not that hard to
understand. The earth’s atmosphere is composed of
many different elements including carbon and
nitrogen. The basic nitrogen atom has 7 protons
and 7 neutrons. There are 3 types of Carbon :
carbon 12, carbon 13, and carbon 14. Carbon 12 is
most common, occurring 98.9% of the time. It has 6
neutrons and 6 protons. In rare instances--about
0.000000001% or 10^(-9)% of the time--carbon takes the
form carbon 14, with 6 protons and 8 neutrons.
Cosmic rays from the sun constantly bombard our
atmosphere creating neutrons. Once in a while a
neutron will collide with a nitrogen atom. The
neutron knocks a proton free and takes its place,
creating a carbon atom. The nitrogen atom now has
six protons and 8 neutrons, transforming it to
carbon because it only has 6 protons. Note that
when an atomic explosion also involves the movement
of protons. By definition carbon is an atom with
six protons. Unlike a normal carbon atom, however,
this new atom (that was originally nitrogen) now
has 8 neutrons, making it an isotope. As noted
above, the atom is also radioactive.
All life on this planet is carbon based.
Through photosynthesis plants absorb the carbon
from the atmosphere (CO2 + H2O + sunlight yields C6H12O6 (or
glucose) + O2). Carbon 14 is circulated when an
animal consumes a plants. If that animal is
consumed, the carbon 14 is further circulated. The
process continues up the food chain. When an
organism dies it stops replenishing its carbon 14.
The carbon 14 then starts to decay. At carbon 14’s
half-life--5730 +- 30--half of the carbon has been
depleted. Then another half, and so on. One must
count the carbon 14 atoms to obtain the approximate
age of the organism.

How one counts Carbon 14 :
Thanks to Dr. Willard Libby, a chemist who one
the Nobel prize for his work in radiocarbon dating,
one can measure the amount of carbon 14 in an
organism. Libby devised a method of low level
counting that can be applied to radiocarbon dating.
As stated before, Carbon 14 is a radioactive
isotope of carbon 12. In general, radioactive
substances can be measured using a Geiger counter.
A new method for measuring the extremely small
degree of weak beta decay characteristic of carbon
14 was needed. For this Libby created a way to
introduce the sample directly into the sensitive
volume of a detector.
This was done by converting the sample to solid
carbon, or lampblack and then placing it on a
sleeve that fits into the screen wall of a Geiger
counter. The problem with this was that the
counting order of an unshielded screen wall was
close to 500 counts per minute, whereas carbon 14
decay was known to be about 6 or 7 counts per
minute. This problem was partially solved by
placing the instrument inside an iron shield with 8
inch walls, which reduced the activity in the
detector to 120 counts per minute. The final
solution came when the sample counter was enclosed
by a ring of smaller Geiger counters. Through an
electronic connection any pulse from an outer
Geiger tube would inactivate the sample counter for
about 0.01 seconds. This resulted in an
anticoincidence system that reduced background in
the center counter to 5 counts per minute. The
imperfections of this system limited the maximum
age a substance could be to 23,000 years, and
required a sample of a little more than 10 grams.
By the early 1950's better systems of measurement
had been devised, including a gas counter and a
liquid scintillation system. Even now scientists
are working on more accurate methods of carbon
dating.

Radiocarbon (C-14) Dating
All living organisms absorb radiocarbon, an unstable form of carbon that has a half-life of about 5,730 years. During its lifetime, an organism continually replenishes its supply of radiocarbon by breathing and eating. After the organism dies and becomes a fossil, C-14 continues to decay without being replaced. To measure the amount of radiocarbon left in a fossil, scientists burn a small piece to convert it into carbon dioxide gas. Radiation counters are used to detect the electrons given off by decaying C-14 as it turns into nitrogen. The amount of C-14 is compared to the amount of C-12, the stable form of carbon, to determine how much radiocarbon has decayed and to date the fossil.