CPN MC3 ELITE - Page 53

InstroTek
49
Earth’s Crust
Our task is to measure the density of soils. The elements in the
periodic table we are concerned with are those in the earth’s
crust.
The density of a material is dependent upon its atomic mass
(A). But the count rate in the nuclear density gauge is
dependent on the number of electrons (atomic number (Z)).
For the most materials in the earth’s crust this presents no
problem since the ratio of the atomic number to the atomic
mass (Z/A) is approximately 0.5.
ELEMENT
SYMBOL
No.
(Z)
MASS
(A)
Z/A
% EARTH’S
CRUST
Oxygen
O
8
16.00
0.5000
49.9%
Silicon
Si
14
28.09
0.4984
26.0%
Aluminum
Al
13
26.98
0.4818
7.3%
Iron
Fe
26
55.85
0.4655
4.1%
Calcium
Ca
gamm 20
40.08
0.4990
3.2%
Sodium
Na
11
22.99
0.4785
2.3%
Potassium
K
19
39.10
0.4895
2.3%
Magnesium
Mg
12
24.31
0.4936
2.1%
Other
2.8%
Hydrogen
H
1
1.008
0.9921
Water
H
2
O
10
18.016
0.5551