handbook of carbon, graphite, diamond and fullerenes

The Element Carbon 21
loses a proton (going from seven to six), thus decreasing in atomic number
and becoming 14 C.
As mentioned above, 14 C is a radioactive isotope and decays spontaneously
by emitting p" particles, thus forming a nitrogen atom, as shown
schematically in Fig. 2.3. The processes of formation and decay are in
equilibrium in the atmosphere and the amount of 14 C remains essentially
constant at a low level. Much of this 14 C is found in the atmospheric carbon
dioxide.
i 4 Catom
(Parent)
6 Protons
6 Neutrons
6 Electrons
14 N atom
(Daughter)
7 Protons
7 Neutrons
7 Electrons
A neutron of the 14 C atom spontaneously forms
a proton and a beta particle which becomes the
new electron of the nitrogen atom.
Figure 2.3. Decay of the 14 C radioactive carbon isotope.' 8 '
Carbon-14 in Living and Dead Matter. Plants continuously absorb
CO2 and, consequently, maintain a constant level of 14 C in their tissues.
Animals consume plants (or other plant-eating animals) and thus every
living thing contains carbon that includes a small amount of 14 C in
essentially the same ratio as the 14 C in the atmosphere. This amount is only
1 x 10 8 of the amount of 12 C.
After death, 14 C is no longer replaced and, through the radioactive
decay process, remains in dead matter in a steadily diminishing amount as
time goes by. This amount can be measured (and the years since death
readily computed) by counting the number of p" particles emitted by the