Other Instrumental Methods in Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 330

The hazards due to ionizing radiations and radioactivities are unique from common
nonradioactive chemicals. They can be lethal at a high dose, but in most cases the
effects are not apparent and are hard to assess. The effects of lower levels of
exposure can lead to cell mutation and the development of cancer, which may have
consequences for offspring rather than for the parent. Fortunately, the instrumenta-
tions for the detection of ionization and radioactivity are readily available.
Table 12.3 is a short list of some common radioactive nuclides (radionuclides).
Of the listed radionuclides, carbon-14 ( 14 C ) and tritium ( 1 H) are produced in the
upper atmosphere as a result of cosmic radiations and their subsequent incorporation
into the elemental cycles. Note the common notation A X, where Z is the atomic
number and A is the mass number of the element X. The atomic number is also
the number of protons contained in its nucleus and the mass number is the sum of the
number of neutrons and protons in a nucleus. Hence, the radioactive 14 C has six
protons and eight neutrons, whereas its nonradioactive isotope carbon-13 ( 13 C) has
the same number of protons but different number of neutrons.

Table 12.3 Characteristics of common radioactive nuclides

Nuclide Abundance (%) Half-life Radiations and energy (MeV)

3 H

b (0.0186)

- 12.26 y

14 C

b (0.155) - 5720 y

32 P

b (1.71) - 14.3 d

35 S

b (0.167)

- 87 d

90 Sr

b (0.54) - 29 y

137 Cs

b (0.51)

- 39 y

222 Rn

- 3.8 d a (N.A.)

226 Ra

100 1622 y a (4.78)

234 U

210 5 y

0.0056 a (4.77, 4.72)

235 U

710 8 y 0.7205 a (4.39); g (0.18, 0.14)

238 U

510 9 y

99.27 a (4.19)

MeV¼ one million electron volts. Adapted from Pecsok et al. (1968).

The first four radionuclides ( 3 H, 14 C, 32 P, 35 S) in Table 12.3 are of more
importance in environmental research on the fate and transport studies using
radiolabeled compounds. An important application is to label test contaminant with
radionuclides and then study its degradation/transformation pathways. None of these
four radionuclides are natural origins. The half-lives for 32 P and 35 S are short in
terms of days but the half-lives of 3 H and 14 C are very long. For example, 14 C has a
half-life of 5720 years.
Table 12.3 also includes several other radionuclides with environmental
significance. For example, uranium is the basis of nuclear power and nuclear fuel
cycle. Uranium present in its two principal isotopes, 238 U and 235 U, is widely
distributed in natural environment and is present in significant levels in many
granitic strata. In nuclear industries, uranium is mined, concentrated, processed, and
disposed of in the environment in a large quantity. Radium is one of the decay