There are many ways to date finds from the past, depending on
the kind of material and on the precision requested.
Here are the most used ways:
|
Tecniche
basate sugli isotopi
|
|
from uranium to lead |
mineral |
from 1 million to 4.5 bilions years |
|
from rubidium to strontium |
mineral |
from 60 million a 4.5 bilions years |
|
da potassium to
argon |
mineral |
from 10000 to 3 bilions years |
|
unbalance of the family of the uranium |
mineral, shells, bones, teeth, coral |
fom 0 to 400000 years |
|
carbon 14 |
mineral, shells, wood, bones, teeth, water |
from 0 to 40000 years |
|
Tecniche
di esposizione a radiazioni
|
|
trace of fission |
mineral, natural glass |
from 500000 to 1 bilions years |
|
Glow Curve |
mineral, natural glass |
from 0 to 500000 years |
|
Glow Curve in optic stimulation
|
mineral |
from
0 to 500000 years |
|
electronic resonance of spin |
mineral, enamel of the teeth, shells, coral |
from 1000 to 1 million years |
|
Altre
tecniche
|
|
staircase of the inversion magnetic |
mineral |
from 780000 to 200 million years |
|
racemization of the amino acids |
carbonate of biological origin |
from 500 to 300000 years |
|
hydration of the ossidiana |
natural glass |
from 500 to 200000 years |
|
dendochronology |
rings of the trees |
from 0 to 12000 years |
|
lichenometria |
lichens |
from 100 to 9000 years |
Often, for a better reliability, various systems can be used
to be able to compare the results. The most used system for
Egyptian finds is undoubtedly the carbon 14. This method is
based upon the unstable equilibrium of the atoms present in
carbon 12 and carbon 14 that are in an organism after death.
Every atom has in its nucleus a number of protons (positive
charges) and of neutrons (neutral charges). Usually protons and
neutrons are present in the same number. The atom of the carbon
is made of 6 protons and 6 neutrons and from this, the name
carbon 12. Some atoms instead, have a different number of
neutrons. In this case, these atoms, are called isotopi. So the
atom in the carbon that has 8 neutrons and 6 protons is an
isotopo of carbon called carbon 14. It is radioactive and it is
formed after collision between the particles from space and
atoms of nitrogen present in the atmosphere. Living plants and
animals have a constant quantity of carbon 12 and carbon 14, but
after death the atoms of carbon 14 begin to decrease changing
into atoms of nitrogen 14. The speed with which they decrease is
known so, comparing the level of carbon 14 with the total number
of carbon present in the rests, it’s possible to calculate the
time passed since the death. The number of atoms in carbon 14 is
halved every 5730 years. |
|
