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
Curium	Z = 96																							242 cm		244 cm		246 cm
Americium	Z = 95																						240 am	241 On	242 On	243 On	244 On
plutonium	Z = 94																			236 Pu	237 Pu	238 Pu	239 Pu	240 pu	241 Pu	242 Pu	243 Pu	244 Pu
neptunium	Z = 93																	233 Np	234 Np	235 Np	236 Np	237 Np	238 Np	239 Np	240 Np
uranium	Z = 92															230 U	231 U	232 U	233 U	234 U	235 U	236 U	237 U	238 U	239 U	240 U
Protactinium	Z = 91															229 Pa	230 Pa	231 Pa	232 Pa	233 Pa	234 Pa
Thorium	Z = 90													226 Th	227 Th	228 Th	229 Th	230 th	231 Th	232 Th	233 Th	234 Th
Actinium	Z = 89													225 Ac	226 Ac	227 Ac	228 Ac
radium	Z = 88										221 Ra	222 ra	223 ra	224 ra	225 ra	226 Ra	227 ra	228 ra
Francium	Z = 87											221 Fr	222 Fr	223 Fr
radon	Z = 86								217 para	218 para	219 para	220 para		222 para
Astatine	Z = 85							215 at		217 at	218 at	219 at
polonium	Z = 84			210 Po	211 Po	212 Po	213 Po	214 Po	215 Po	216 Po		218 Po
Bismuth	Z = 83			209 bi	210 bi	211 bi	212 bi	213 bi	214 Bi	215 bi
lead	Z = 82	206 Pb	207 Pb	208 Pb	209 Pb	210 Pb	211 Pb	212 Pb		214 Pb
Thallium	Z = 81	205 Tl	206 Tl	207 Tl	208 Tl	209 Tl	210 Tl
mercury	Z = 80			206 ed
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:		Uranium-radium series					Uranium actinium series					(Plutonium) thorium series					(Plutonium) Neptunium series					(Arrows not to scale)
		continuation					continuation					continuation					continuation

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
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

• Fajans-Soddyian displacement theorems

Web links

Commons : decay series  - collection of images, videos, and audio files

Individual evidence

1. ↑ Karlsruhe nuclide map . Reprint of the 6th edition. Karlsruhe 1998
2. ↑ 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
3. ^ EB Paul: Nuclear and Particle Physics. North-Holland, 1969, p. 41
4. ^ CM Lederer, JM Hollander, I. Perlman: Table of Isotopes. 6th edition. Wiley & Sons, New York 1968
5. ↑ https://www.uni-oldenburg.de/fileadmin/user_upload/chemie/ag/occhris/download/pdf1.pdf