Decay series
A decay series in the general sense is the sequence of the successive products of a radioactive decay . It is formed when one radionuclide is transformed into another, this into a third, etc. (“disintegrates”). The first resulting nuclide is daughter nuclide , called the daughter nuclide the following Enkelnuklid that following the Enkelnuklid Urenkelnuklid etc.
From an existing amount of an unstable nuclide, a mixture of nuclides is formed through decay, which follow it in the decay series before all atomic nuclei have passed through the series to the end nuclide at some point. In the mixture, nuclides with a short half-life are only present in small amounts, while those with a longer half-life accumulate more strongly.
The three natural series of decays
The decay series of the three primordial radionuclides uranium- 238, uranium-235 and thorium- 232, also called naturally radioactive families , are of practical and historical importance . They arise from alpha and beta decays which alternate more or less regularly. Some of the nuclides involved also have the alternative but rare type of decay spontaneous fission ; it leads out of the respective decay series and is not considered here.
An alpha decay reduces the mass number of the atomic nucleus by 4 units, a beta decay leaves it unchanged. If one writes the mass number A as A = 4 n + m (where n is any natural number and m is one of the numbers 0, 1, 2 or 3), then m always remains constant within such a decay series. The three initial nuclides mentioned have different values of m . Hence generated
- Uranium-238 the "(4n + 2) series" or uranium-radium series with the end nuclide lead -206,
- Uranium-235 the "(4n + 3) series" or uranium-actinium series with the end nuclide lead-207,
- Thorium-232 the "(4n) series" or thorium series with the end nuclide lead-208.
Thorium-232 is primordial, but according to current knowledge, its predecessor nuclides up to plutonium-244 are also present on Earth.
A fourth series of decays
In the above (4 n + m ) systematics a series with m = 1 is “missing” . Since there is no primordial nuclide with A = 4 n +1 in the mass number range of uranium and thorium , such a decay series does not occur in nature ( more) before. For the sake of the system, however, the decay series of the artificially producible nuclides plutonium -241 or neptunium -237, the neptunium series , is regarded as this missing fourth series. Only the last radionuclide in this series, bismuth -209, is still present because of its extremely long half-life. It was long thought to be the final nuclide until it was discovered in 2003 that it is an alpha emitter with a half-life of 19 trillion years . The final nuclide is therefore thallium -205.
Location in the nuclide map
Neutron count | N = | 124 | 125 | 126 | 127 | 128 | 129 | 130 | 131 | 132 | 133 | 134 | 135 | 136 | 137 | 138 | 139 | 140 | 141 | 142 | 143 | 144 | 145 | 146 | 147 | 148 | 149 | 150 | |
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Curium | Z = 96 |
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242 cm |
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244 cm |
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246 cm |
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Americium | Z = 95 |
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240 am |
241 On |
242 On |
243 On |
244 On |
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plutonium | Z = 94 |
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236 Pu |
237 Pu |
238 Pu |
239 Pu |
240 pu |
241 Pu |
242 Pu |
243 Pu |
244 Pu |
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neptunium | Z = 93 |
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233 Np |
234 Np |
235 Np |
236 Np |
237 Np |
238 Np |
239 Np |
240 Np |
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uranium | Z = 92 |
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230 U |
231 U |
232 U |
233 U |
234 U |
235 U |
236 U |
237 U |
238 U |
239 U |
240 U |
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Protactinium | Z = 91 |
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229 Pa |
230 Pa |
231 Pa |
232 Pa |
233 Pa |
234 Pa |
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Thorium | Z = 90 |
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226 Th |
227 Th |
228 Th |
229 Th |
230 th |
231 Th |
232 Th |
233 Th |
234 Th |
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Actinium | Z = 89 |
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225 Ac |
226 Ac |
227 Ac |
228 Ac |
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radium | Z = 88 |
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221 Ra |
222 ra |
223 ra |
224 ra |
225 ra |
226 Ra |
227 ra |
228 ra |
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Francium | Z = 87 |
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221 Fr |
222 Fr |
223 Fr |
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radon | Z = 86 |
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217 para |
218 para |
219 para |
220 para |
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222 para |
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Astatine | Z = 85 |
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215 at |
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217 at |
218 at |
219 at |
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polonium | Z = 84 |
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210 Po |
211 Po |
212 Po |
213 Po |
214 Po |
215 Po |
216 Po |
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218 Po |
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Bismuth | Z = 83 |
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209 bi |
210 bi |
211 bi |
212 bi |
213 bi |
214 Bi |
215 bi |
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lead | Z = 82 |
206 Pb |
207 Pb |
208 Pb |
209 Pb |
210 Pb |
211 Pb |
212 Pb |
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214 Pb |
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Thallium | Z = 81 |
205 Tl |
206 Tl |
207 Tl |
208 Tl |
209 Tl |
210 Tl |
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mercury | Z = 80 |
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206 ed |
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Neutron count | N = | 124 | 125 | 126 | 127 | 128 | 129 | 130 | 131 | 132 | 133 | 134 | 135 | 136 | 137 | 138 | 139 | 140 | 141 | 142 | 143 | 144 | 145 | 146 | 147 | 148 | 149 | 150 | |
Legend: |
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Uranium-radium series |
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Uranium actinium series |
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(Plutonium) thorium series |
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(Plutonium) Neptunium series |
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(Arrows not to scale) | |||||||||||||||||||
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continuation |
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continuation |
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continuation |
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continuation |
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Historical names
In the classical period of research into radioactive decay series - i.e. in the early 20th century - the various nuclides were given different names, which indicated that they belonged to a natural decay series and that their properties were similar (e.g. radon , Thoron and actinone all noble gases):
Current name | Historical name | Long version of the name |
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238 U | U I | Uranium I |
235 U | AcU | Actinuran |
234 U | U II | Uranium II |
234m Pa | UX 2 | Uranium X 2 |
234 Pa | UZ | Uranium Z |
231 Pa | Pa | Protactinium |
234 Th | UX 1 | Uranium X 1 |
232 Th | Th | Thorium |
231 Th | UY | Uranium Y |
230 th | Io | Ionium |
228 Th | RdTh | Radiothoroid |
227 Th | RdAc | Radioactinium |
228 Ac | MsTh 2 | Mesothore 2 |
227 Ac | Ac | Actinium |
228 ra | MsTh 1 | Mesothore 1 |
226 Ra | Ra | radium |
224 ra | ThX | Thorium X |
223 ra | AcX | Actinium X |
223 Fr | AcK | Actinium K |
222 para | Marg | radon |
220 para | Tn | Thoron |
219 para | On | Actinone |
218 Po | RaA | Radium A |
216 Po | ThA | Thorium A |
215 Po | AcA | Actinium A |
214 Po | RaC ' | Radium C ' |
212 Po | ThC ' | Thorium C ' |
211 Po | AcC ' | Actinium C ' |
210 Po | RaF | Radium F |
214 Bi | RaC | Radium C |
212 bi | ThC | Thorium C |
211 bi | AcC | Actinium C |
210 bi | RaE | Radium E |
214 Pb | RaB | Radium B |
212 Pb | ThB | Thorium B |
211 Pb | AcB | Actinium B |
210 Pb | Wheel | Radium D |
208 Pb | ThD | Thorium D |
207 Pb | AcD | Actinium D |
206 Pb | RaG | Radium G |
210 Tl | RaC " | Radium C " |
208 Tl | ThC " | Thorium C " |
207 Tl | AcC " | Actinium C " |
The three natural decay series would look like this in this old notation:
- Uranium-radium series: U I → UX 1 → UX 2 (→ UZ) → U II → Io → Ra → Rn → RaA → RaB → RaC → RaC '(or RaC ") → RaD → RaE → RaF → RaG
- Uranium-actinium series: AcU → UY → Pa → Ac → RdAc (or AcK) → AcX → An → AcA → AcB → AcC → AcC "(or AcC ') → AcD
- Thorium series: Th → MsTh 1 → MsTh 2 → RdTh → ThX → Tn → ThA → ThB → ThC → ThC '(or ThC ") → ThD
Calculation of the concentration of nuclides in a decay series
Nuclides decay according to first-order kinetics (cf. law of decay ), so that the time-dependent concentration of an individual nuclide can be calculated quite easily. The question becomes much more complicated when the nuclide is continuously reproduced as a member of a decay series from precursor nuclides. Jens Christoffers (1986) provides a short and clear way of calculating his concentration under these conditions; the author also gives an algorithm for programming the calculation.
See also
Web links
Individual evidence
- ↑ Karlsruhe nuclide map . Reprint of the 6th edition. Karlsruhe 1998
- ↑ DC Hoffman, FO Lawrence, JL Mewherter, FM Rourke: Detection of Plutonium-244 in Nature. In: Nature 234, 1971, pp. 132-134, doi: 10.1038 / 234132a0
- ^ EB Paul: Nuclear and Particle Physics. North-Holland, 1969, p. 41
- ^ CM Lederer, JM Hollander, I. Perlman: Table of Isotopes. 6th edition. Wiley & Sons, New York 1968
- ↑ https://www.uni-oldenburg.de/fileadmin/user_upload/chemie/ag/occhris/download/pdf1.pdf