What Are Isotopes and What Can Be Learned From Them?

Fig. 3: Environmental isotopes used in hydrology

Isotope Average natural
abundance atoms % 		Half-life
1H
2H (deuterium)
3H (tritium) 		99.985
0.015
10-15 		Stable
Stable
12.43 years
3He (*)
4He (*) 		0.00013
99.99987 		Stable
Stable
12C
13C
14C 		98.89
1.11
1.2-10-10 		Stable
Stable
5730
14N
15N 		99.63
0.37 		Stable
Stable
16O
18O 		99.76
0.20 		Stable
Stable
32S
32S 		95.0
4.22 		Stable
Stable
35Cl
36Cl
37Cl 		75.53

24.47 		Stable
300 000 years
Stable