330 ENVIRONMENTAL ENGINEEUG
hydrogen gas in a reactor and with H+ ions in the reactor cooling water. Containment
of tritium is thus difficult.
In a fission reaction, not all of the neutrons will collide with a fissile nucleus to
initiate fission. Some neutrons will collide, and react, with the fuel container and the
reactor vessel itself, producing neutron activation products. Some of these are relatively
long-lived, notably CO-60 (half-life, 5.2 years) and Fe-59 (half-life, 45 days). Other
neutrons react with nonfissile isotopes, like U-238, as in the reaction
93Np239 = 9q~239 + -le 0.
Pu-239, “weapons-grade” plutonium, has a half-life of 24,600 years. Other isotopes
of plutonium are formed also. Radionuclides like U-238, from which fissile material
like plutonium can be produced by nuclear reaction, are known as fertile isotopes.
Another isotope of plutonium, Pu-241, decays by beta emission to Am-241 (half-life,
433 years). Am-241 is commonly used as an ion producer in smoke detectors.
Each uranium isotope is part of a decay series; when U-238 decays, the daugh-
ter element is also radioactive and decays, producing another radioactive daughter,
Table 16-9. U-238 Decay SeriesIsotope me of emission Half-lifeU-238
Th-234
Pa-234
U-234
Th-230
Ra-226
Rn-222
PO-21 8
At-2^1 8
Pb-214
Bi-214
PO-214
Tl-2 10
Pb-210
Bi-210
Po-210
Tl-206
Pb-206Alpha
Beta
Beta
Alpha
Alpha
Alpha
Alpha
Alphatbeta
Alpha
Beta
Alphabeta
Alpha
Beta
Beta
Alphaheta
Alpha
Bedgamma4.5 x^109 years
24.1 days
1.18 min
248,000 years
80,000 years
1620 years
3.28 days
3.05 min
2s
26.8 min
19.7 min
0.00016 s
1.32 mins
19.4 years
5.0 days
138.4 days
4.2 min
StableNote. The chain branches where two emissions are listed, e.g., Ph-214 and
At-218 are both daughters of Po-218.