Radium Series (or Uranium Series)
The 4n+2 chain of 238U is commonly called the "radium series" (sometimes "uranium series"). Beginning with naturally occurring uranium-238, this series includes the following elements: astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any uranium-containing sample, whether metal, compound, or mineral.
| Nuclide | Historic name (short) | Historic name (long) | Decay mode | Half-life | MeV | Decay product |
|---|---|---|---|---|---|---|
| 238U | U | Uranium | α | 4.468·109 a | 4.270 | 234Th |
| 234Th | UX1 | Uranium X1 | β- | 24.10 d | 0.273 | 234mPa |
| 234mPa | UX2 | Uranium X2 | β- 99.84% IT 0.16% |
1.16 min | 2.271 0.074 |
234U 234Pa |
| 234Pa | UZ | Uranium Z | β- | 6.70 h | 2.197 | 234U |
| 234U | UII | Uranium two | α | 245500 a | 4.859 | 230Th |
| 230Th | Io | Ionium | α | 75380 a | 4.770 | 226Ra |
| 226Ra | Ra | Radium | α | 1602 a | 4.871 | 222Rn |
| 222Rn | Rn | Radon | α | 3.8235 d | 5.590 | 218Po |
| 218Po | RaA | Radium A | α 99.98% β- 0.02% |
3.10 min | 6.115 0.265 |
214Pb 218At |
| 218At | α 99.90% β- 0.10% |
1.5 s | 6.874 2.883 |
214Bi 218Rn |
||
| 218Rn | α | 35 ms | 7.263 | 214Po | ||
| 214Pb | RaB | Radium B | β- | 26.8 min | 1.024 | 214Bi |
| 214Bi | RaC | Radium C | β- 99.98% α 0.02% |
19.9 min | 3.272 5.617 |
214Po 210Tl |
| 214Po | RaC' | Radium C' | α | 0.1643 ms | 7.883 | 210Pb |
| 210Tl | RaC" | Radium C" | β- | 1.30 min | 5.484 | 210Pb |
| 210Pb | RaD | Radium D | β- | 22.3 a | 0.064 | 210Bi |
| 210Bi | RaE | Radium E | β- 99.99987% α 0.00013% |
5.013 d | 1.426 5.982 |
210Po 206Tl |
| 210Po | RaF | Radium F | α | 138.376 d | 5.407 | 206Pb |
| 206Tl | β- | 4.199 min | 1.533 | 206Pb | ||
| 206Pb | – | stable | – | – |
The mean lifetime of 238U is 1.41×1017 seconds divided by 0.693 (or multiplied by 1.443), i.e. ca. 2×1017 seconds, so 1 mole of 238U emits 3×106 alpha particles per second, producing the same number of thorium-234 (Th-234) atoms. In a closed system an equilibrium would be reached, with all amounts except for lead-206 and 238U in fixed ratios, in slowly decreasing amounts. The amount of Pb-206 will increase accordingly while that of 238U decreases; all steps in the decay chain have this same rate of 3×106 decayed particles per second per mole 238U.
Thorium-234 has a mean lifetime of 3×106 seconds, so there is equilibrium if one mole of 238U contains 9×1012 atoms of thorium-234, which is 1.5×10−11 mole (the ratio of the two half-lives). Similarly, in an equilibrium in a closed system the amount of each decay product, except the end product lead, is proportional to its half-life.
As already touched upon above, when starting with pure 238U, within a human timescale the equilibrium applies for the first three steps in the decay chain only. Thus, for one mole of 238U, 3×106 times per second one alpha and two beta particles and gamma ray are produced, together 6.7 MeV, a rate of 3 µW. Extrapolated over 2×1017 seconds this is 600 gigajoules, the total energy released in the first three steps in the decay chain.
| Lighter: uranium-237 |
uranium-238 is an isotope of uranium |
Heavier: uranium-239 |
| Decay product of: plutonium-242 (α) protactinium-238 (β-) |
Decay chain of uranium-238 |
Decays to: thorium-234 (α) |
Read more about this topic: Uranium-238
Famous quotes containing the word series:
“As Cuvier could correctly describe a whole animal by the contemplation of a single bone, so the observer who has thoroughly understood one link in a series of incidents should be able to accurately state all the other ones, both before and after.”
—Sir Arthur Conan Doyle (1859–1930)