TABLE 1b

THE DECAY CHAINS OF URANIUM AND THORIUM


238 U , 234 U
238 U > 234 Th > 234 Pa > 234 U > 230 Th > 226 Ra > 222 Rn > 218 Po > 214 Pb > 214 Bi > 214 Po > 210 Pb > 210 Bi 206 Tl > 206 Pb (stable)

235 U
235 U > 231 Th > 227 Ac > 223 Fr > 219 Ac > 215 Bi > 211 Pa > 211 Bi > 207 Tl > 207 Pb (stable)

232 Th
232 Th > 228 Ra > 288 Ac > 228 Th > 224 Ra > 220 Rn > 216 Po > 212 Pb >212 Bi > 212 Po > 208 Tl > 208 Pb (stable)

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208 Tl 208 Pb (stable)

    The various isotopes of uranium decay either to radioactive thorium or radioactive neptunium. The most common isotope of uranium, 238 U, decays to 234 Th. The various isotopes of thorium decay to radioactive isotopes of radium, the most important of which is 226 Ra, a decay product of 230 Th. 226 Ra decays to 222 Rn, the only gas in the decay series. The radioactive decay products or radon are radioactive isotopes of lead, bismuth, and polonium, until the chain ends with stable isotopes of lead (Faw and Shultis 1993).


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