Environmental Engineering Reference
In-Depth Information
products of uranium ( 238 U). It has four naturally occurring isotopes 222 Ra, 224 Ra,
226 Ra, and 228 Ra. Of particular importance is the Radon-222, which is a daughter
product of 226 Ra. It is of particular environmental importance because radon occurs
naturally as a result of the radioactive decays from rocks and soils. Because radon
exists in the form of a radioactive gas, its presence in buildings has called for the
second leading cause of lung cancer in the United States.
In contrast to stable isotopes (e.g., 3 H and 14 C as compared to 1 H and 12 C), one
unique property of all radionuclides is their spontaneous decay process (disintegra-
tion) to their ultimate stable forms. During the radioactive decay process,
electromagnetic radiations are emitted. The emissions can be in various forms
depending on the nature of the specific radionuclides. These various forms of
radiations, that is, a particles (helium nucleus), b particles (electrons), and g rays
(photons) are discussed below.
Beta (b) radiation, as shown in Table 12.3 for several light elements, is the
result of the following nuclear reactions:
A
Zþ1 Y þb þ g
A
Z X !
ð12
:
Z X !
Z1 Y þb þ þ g
A
ð12
:
where b þ and b (or
0
0
þ1 b) denote negatrons and positrons, respectively.
Negatrons are essentially the electrons in terms of the mass and charge but they have
the origin of nuclear reactions. Positrons carry the same positive charge equal in
magnitude to that of the negatrons. As shown in Eqs 12.4 and 12.5, many b radiations
accompany the emission of g-rays, although 3 H and 14 C are the exceptions. Gamma
(g) radiation is a high-energy electromagnetic radiation (photons) with a wavelength
shorter than UV. It is identical to a high-energy X-ray with an exception that their
sources are different. Unlike b particles, g-rays ( 0 g) do not carry charge and mass.
Alpha (a) radiation occurs only for heavy nuclides with an atomic number (A)
greater than 90. Thus, radon, radium, and uranium all radiate a particles, which
carry þ2 charge and a mass of 4 atomic mass unit (amu). Therefore, a particles
are essentially the helium nuclei that have been stripped of their two electrons,
that is, 2 He .
1 b and
Preservation and Measurement of Radioactive Samples
The general principles of sample preservations for most radioactive nuclides are
the same as those described in Chapter 4 for the preservation of metals (Table 12.4).
With an exception of tritium, acid preservation to pH
2 is all that is required.
Either plastic or glass containers are acceptable, although, plastic ones are
preferred to prevent any breakage during sample transportation. Extra safety
precautions that are not usually associated with common chemical analysis should
be excised for radioactive materials. For personal protection, it is imperative to
wear monitoring devices (personal film badges) at all times. One should also be
aware of the different health hazards posted by various particles described in the
preceding section. The penetration power is in an increasing order of a, b, and g
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