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Isotopes of lead
Isotopes of lead
Isotopes of lead
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Isotopes of lead (82Pb)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
202Pb synth 5.25×104 y ε 202Tl
204Pb 1.40% stable
205Pb synth 1.70×107 y ε 205Tl
206Pb 24.1% stable
207Pb 22.1% stable
208Pb 52.4% stable
209Pb trace 3.235 h β− 209Bi
210Pb trace 22.2 y β− 210Bi
α 206Hg
211Pb trace 36.16 min β− 211Bi
212Pb trace 10.627 h β− 212Bi
214Pb trace 27.06 min β− 214Bi
Isotopic abundances vary greatly by sample[2]
Standard atomic weight Ar°(Pb)

Lead (82Pb) has four observationally stable isotopes: 204Pb, 206Pb, 207Pb, 208Pb. Lead-204 is entirely a primordial nuclide and is not a radiogenic nuclide. The three isotopes lead-206, lead-207, and lead-208 represent the ends of three decay chains: the uranium series (or radium series), the actinium series, and the thorium series, respectively; a fourth decay chain, the neptunium series, terminates with the thallium isotope 205Tl. The three series terminating in lead represent the decay chain products of long-lived primordial 238U, 235U, and 232Th. Each isotope also occurs, to some extent, as primordial isotopes that were made in supernovae, rather than radiogenically as daughter products. The fixed ratio of lead-204 to the primordial amounts of the other lead isotopes may be used as the baseline to estimate the extra amounts of radiogenic lead present in rocks as a result of decay from uranium and thorium. This is the basis for lead–lead dating and uranium–lead dating.

The longest-lived radioisotopes, both decaying by electron capture, are 205Pb with a half-life of 17.0 million years and 202Pb with a half-life of 52,500 years. A shorter-lived naturally occurring radioisotope, 210Pb with a half-life of 22.2 years, is useful for studying the sedimentation chronology of environmental samples on time scales shorter than 100 years.[4]

The heaviest stable isotope, 208Pb, belongs to this element. (The more massive 209Bi, long considered to be stable, actually has a half-life of 2.01×1019 years.) 208Pb is also a doubly magic isotope, as it has 82 protons and 126 neutrons.[5] It is the heaviest doubly magic nuclide known.

The four primordial isotopes of lead are all observationally stable, meaning that they are predicted to undergo radioactive decay but no decay has been observed yet. These four isotopes are predicted to undergo alpha decay and become isotopes of mercury which are themselves radioactive or observationally stable.

There are trace quantities existing of the radioactive isotopes 209-214. The largest and most important is lead-210 as it has by far the longest half-life (22.2 years) and occurs in the abundant uranium decay series. Lead-211, −212, and −214 are present in the decay chains of uranium-235, thorium-232, and uranium-238, further, making these three lead isotopes also detectable in natural sources. The more minute traces of lead-209 arise from three rare decay branches: the beta-delayed-neutron decay of thallium-210 (in the uranium series), the last step of the neptunium series, traces of which are produced by neutron capture in uranium ores, and the very rare cluster decay of radium-223 (yielding also carbon-14). Lead-213 also occurs in a minor branch of the neptunium series. Lead-210 is particularly useful for helping to identify the ages of samples by measuring its ratio to lead-206 (both isotopes are present in a single decay chain).[6]

In total, 43 lead isotopes have been synthesized, from 178Pb to 220Pb.

List of isotopes

[edit]


Nuclide
[n 1] 		Historic
name 		Z N Isotopic mass (Da)[7]
[n 2][n 3] 		Half-life[1]
 Decay
mode[1]
[n 4] 		Daughter
isotope
[n 5][n 6] 		Spin and
parity[1]
[n 7][n 8] 		Natural abundance (mole fraction)
Excitation energy[n 8] Normal proportion[1] Range of variation
178Pb 82 96 178.003836(25) 250(80) μs α 174Hg 0+
β+? 178Tl
179Pb 82 97 179.002(87) 2.7(2) ms α 175Hg (9/2−)
180Pb 82 98 179.997916(13) 4.1(3) ms α 176Hg 0+
181Pb 82 99 180.996661(91) 39.0(8) ms α 177Hg (9/2−)
β+? 181Tl
182Pb 82 100 181.992674(13) 55(5) ms α 178Hg 0+
β+? 182Tl
183Pb 82 101 182.991863(31) 535(30) ms α 179Hg 3/2−
β+? 183Tl
183mPb 94(8) keV 415(20) ms α 179Hg 13/2+
β+? 183Tl
IT? 183Pb
184Pb 82 102 183.988136(14) 490(25) ms α (80%) 180Hg 0+
β+? (20%) 184Tl
185Pb 82 103 184.987610(17) 6.3(4) s β+ (66%) 185Tl 3/2−
α (34%) 181Hg
185mPb[n 9] 70(50) keV 4.07(15) s α (50%) 181Hg 13/2+
β+? (50%) 185Tl
186Pb 82 104 185.984239(12) 4.82(3) s β+? (60%) 186Tl 0+
α (40%) 182Hg
187Pb 82 105 186.9839108(55) 15.2(3) s β+ (90.5%) 187Tl 3/2−
α (9.5%) 183Hg
187mPb[n 9] 19(10) keV 18.3(3) s β+ (88%) 187Tl 13/2+
α (12%) 183Hg
188Pb 82 106 187.980879(11) 25.1(1) s β+ (91.5%) 188Tl 0+
α (8.5%) 184Hg
188m1Pb 2577.2(4) keV 800(20) ns IT 188Pb 8−
188m2Pb 2709.8(5) keV 94(12) ns IT 188Pb 12+
188m3Pb 4783.4(7) keV 440(60) ns IT 188Pb (19−)
189Pb 82 107 188.980844(15) 39(8) s β+ (99.58%) 189Tl 3/2−
α (0.42%) 185Hg
189m1Pb 40(4) keV 50.5(21) s β+ (99.6%) 189Tl 13/2+
α (0.4%) 185Hg
IT? 189Pb
189m2Pb 2475(4) keV 26(5) μs IT 189Pb 31/2−
190Pb 82 108 189.978082(13) 71(1) s β+ (99.60%) 190Tl 0+
α (0.40%) 186Hg
190m1Pb 2614.8(8) keV 150(14) ns IT 190Pb 10+
190m2Pb 2665(50)# keV 24.3(21) μs IT 190Pb (12+)
190m3Pb 2658.2(8) keV 7.7(3) μs IT 190Pb 11−
191Pb 82 109 190.9782165(71) 1.33(8) min β+ (99.49%) 191Tl 3/2−
α (0.51%) 187Hg
191m1Pb 58(10) keV 2.18(8) min β+ (99.98%) 191Tl 13/2+
α (0.02%) 187Hg
191m2Pb 2659(10) keV 180(80) ns IT 191Pb 33/2+
192Pb 82 110 191.9757896(61) 3.5(1) min β+ (99.99%) 192Tl 0+
α (0.0059%) 188Hg
192m1Pb 2581.1(1) keV 166(6) ns IT 192Pb 10+
192m2Pb 2625.1(11) keV 1.09(4) μs IT 192Pb 12+
192m3Pb 2743.5(4) keV 756(14) ns IT 192Pb 11−
193Pb 82 111 192.976136(11) 4# min β+? 193Tl 3/2−#
193m1Pb 93(12) keV 5.8(2) min β+ 193Tl 13/2+
193m2Pb 2707(13) keV 180(15) ns IT 193Pb 33/2+
194Pb 82 112 193.974012(19) 10.7(6) min β+ 194Tl 0+
α (7.3×10−6%) 190Hg
194m1Pb 2628.1(4) keV 370(13) ns IT 194Pb 12+
194m2Pb 2933.0(4) keV 133(7) ns IT 194Pb 11−
195Pb 82 113 194.9745162(55) 15.0(14) min β+ 195Tl 3/2-
195m1Pb 202.9(7) keV 15.0(12) min β+ 195Tl 13/2+
IT? 195Pb
195m2Pb 1759.0(7) keV 10.0(7) μs IT 195Pb 21/2−
195m3Pb 2901.7(8) keV 95(20) ns IT 195Pb 33/2+
196Pb 82 114 195.9727876(83) 37(3) min β+ 196Tl 0+
α (<3×10−5%) 192Hg
196m1Pb 1797.51(14) keV 140(14) ns IT 196Pb 5−
196m2Pb 2694.6(3) keV 270(4) ns IT 196Pb 12+
197Pb 82 115 196.9734347(52) 8.1(17) min β+ 197Tl 3/2−
197m1Pb 319.31(11) keV 42.9(9) min β+ (81%) 197Tl 13/2+
IT (19%) 197Pb
197m2Pb 1914.10(25) keV 1.15(20) μs IT 197Pb 21/2−
198Pb 82 116 197.9720155(94) 2.4(1) h β+ 198Tl 0+
198m1Pb 2141.4(4) keV 4.12(7) μs IT 198Pb 7−
198m2Pb 2231.4(5) keV 137(10) ns IT 198Pb 9−
198m3Pb 2821.7(6) keV 212(4) ns IT 198Pb 12+
199Pb 82 117 198.9729126(73) 90(10) min β+ 199Tl 3/2−
199m1Pb 429.5(27) keV 12.2(3) min IT 199Pb (13/2+)
β+? 199Tl
199m2Pb 2563.8(27) keV 10.1(2) μs IT 199Pb (29/2−)
200Pb 82 118 199.971819(11) 21.5(4) h EC 200Tl 0+
200m1Pb 2183.3(11) keV 456(6) ns IT 200Pb (9−)
200m2Pb 3005.8(12) keV 198(3) ns IT 200Pb 12+)
201Pb 82 119 200.972870(15) 9.33(3) h β+ 201Tl 5/2−
201m1Pb 629.1(3) keV 60.8(18) s IT 201Pb 13/2+
β+? 201Tl
201m2Pb 2953(20) keV 508(3) ns IT 201Pb (29/2−)
202Pb 82 120 201.9721516(41) 5.25(28)×104 y EC 202Tl 0+
202m1Pb 2169.85(8) keV 3.54(2) h IT (90.5%) 202Pb 9−
β+ (9.5%) 202Tl
202m2Pb 4140(50)# keV 100(3) ns IT 202Pb 16+
202m3Pb 5300(50)# keV 108(3) ns IT 202Pb 19−
203Pb 82 121 202.9733906(70) 51.924(15) h EC 203Tl 5/2−
203m1Pb 825.2(3) keV 6.21(8) s IT 203Pb 13/2+
203m2Pb 2949.2(4) keV 480(7) ms IT 203Pb 29/2−
203m3Pb 2970(50)# keV 122(4) ns IT 203Pb 25/2−#
204Pb[n 10] 82 122 203.9730435(12) Observationally stable[n 11] 0+ 0.014(6) 0.0000–0.0158[9]
204m1Pb 1274.13(5) keV 265(6) ns IT 204Pb 4+
204m2Pb 2185.88(8) keV 66.93(10) min IT 204Pb 9−
204m3Pb 2264.42(6) keV 490(70) ns IT 204Pb 7−
205Pb 82 123 204.9744817(12) 1.70(9)×107 y EC 205Tl 5/2−
205m1Pb 2.329(7) keV 24.2(4) μs IT 205Pb 1/2−
205m2Pb 1013.85(3) keV 5.55(2) ms IT 205Pb 13/2+
205m3Pb 3195.8(6) keV 217(5) ns IT 205Pb 25/2−
206Pb[n 10][n 12] Radium G[10] 82 124 205.9744652(12) Observationally stable[n 13] 0+ 0.241(30) 0.0190–0.8673[9]
206m1Pb 2200.16(4) keV 125(2) μs IT 206Pb 7−
206m2Pb 4027.3(7) keV 202(3) ns IT 206Pb 12+
207Pb[n 10][n 14] Actinium D 82 125 206.9758968(12) Observationally stable[n 15] 1/2− 0.221(50) 0.0035–0.2351[9]
207mPb 1633.356(4) keV 806(5) ms IT 207Pb 13/2+
208Pb[n 16] Thorium D 82 126 207.9766520(12) Observationally stable[n 17] 0+ 0.524(70) 0.0338–0.9775[9]
208mPb 4895.23(5) keV 535(35) ns IT 208Pb 10+
209Pb 82 127 208.9810900(19) 3.235(5) h β− 209Bi 9/2+ Trace[n 18]
210Pb Radium D
Radiolead
Radio-lead 		82 128 209.9841884(16) 22.20(22) y β− (100%) 210Bi 0+ Trace[n 19]
α (1.9×10−6%) 206Hg
210m1Pb 1194.61(18) keV 92(10) ns IT 210Pb 6+
210m2Pb 1274.8(3) keV 201(17) ns IT 210Pb 8+
211Pb Actinium B 82 129 210.9887353(24) 36.1628(25) min β− 211Bi 9/2+ Trace[n 20]
211mPb 1719(23) keV 159(28) ns IT 211Pb (27/2+)
212Pb Thorium B 82 130 211.9918959(20) 10.627(6) h β− 212Bi 0+ Trace[n 21]
212mPb 1335(2) keV 6.0(8) μs IT 212Pb 8+#
213Pb 82 131 212.9965608(75) 10.2(3) min β− 213Bi (9/2+) Trace[n 18]
213mPb 1331.0(17) keV 260(20) ns IT 213Pb (21/2+)
214Pb Radium B 82 132 213.9998035(21) 27.06(7) min β− 214Bi 0+ Trace[n 19]
214mPb 1420(20) keV 6.2(3) μs IT 214Pb 8+#
215Pb 82 133 215.004662(57) 142(11) s β− 215Bi 9/2+#
216Pb 82 134 216.00806(22)# 1.66(20) min β− 216Bi 0+
216mPb 1514(20) keV 400(40) ns IT 216Pb 8+#
217Pb 82 135 217.01316(32)# 19.9(53) s β− 217Bi 9/2+#
218Pb 82 136 218.01678(32)# 14.8(68) s β− 218Bi 0+
219Pb 82 137 219.02214(43)# 3# s
[>300 ns] 		β−? 219Bi 11/2+#
220Pb 82 138 220.02591(43)# 1# s
[>300 ns] 		β−? 220Bi 0+
This table header & footer:
  1. ^ mPb – Excited nuclear isomer.
  2. ^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
  3. ^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
  4. ^ Modes of decay:
    EC: Electron capture


    IT: Isomeric transition
  5. ^ Bold italics symbol as daughter – Daughter product is nearly stable.
  6. ^ Bold symbol as daughter – Daughter product is stable.
  7. ^ ( ) spin value – Indicates spin with weak assignment arguments.
  8. ^ a b # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  9. ^ a b Order of ground state and isomer is uncertain.
  10. ^ a b c Used in lead–lead dating
  11. ^ Believed to undergo α decay to 200Hg with a half-life over 1.4×1020 years; the theoretical lifetime is around ~1035–37 years.[8]
  12. ^ Final decay product of 4n+2 decay chain (the Radium or Uranium series)
  13. ^ Believed to undergo α decay to 202Hg with a half-life over 2.5×1021 years; the theoretical lifetime is ~1065–68 years.[8]
  14. ^ Final decay product of 4n+3 decay chain (the Actinium series)
  15. ^ Believed to undergo α decay to 203Hg with a half-life over 1.9×1021 years; the theoretical lifetime is ~10152–189 years.[8]
  16. ^ Heaviest observationally stable nuclide; final decay product of 4n decay chain (the Thorium series)
  17. ^ Believed to undergo α decay to 204Hg with a half-life over 2.6×1021 years; the theoretical lifetime is ~10124–132 years.[8]
  18. ^ a b Intermediate decay product of 237Np
  19. ^ a b Intermediate decay product of 238U
  20. ^ Intermediate decay product of 235U
  21. ^ Intermediate decay product of 232Th

Lead-206

[edit]
See also: Decay chain

206Pb is the final step in the decay chain of 238U, the "radium series" or "uranium series". In a closed system, over time, a given mass of 238U will decay in a sequence of steps culminating in 206Pb. The production of intermediate products eventually reaches an equilibrium (though this takes a long time, as the half-life of 234U is 245,500 years). Once this stabilized system is reached, the ratio of 238U to 206Pb will steadily decrease, while the ratios of the other intermediate products to each other remain constant.

Like most radioisotopes found in the radium series, 206Pb was initially named as a variation of radium, specifically radium G. It is the decay product of both 210Po (historically called radium F) by alpha decay, and the much rarer 206Tl (radium EII) by beta decay.

Lead-206 has been proposed for use in fast breeder nuclear fission reactor coolant over the use of natural lead mixture (which also includes other stable lead isotopes) as a mechanism to improve neutron economy and greatly suppress unwanted production of highly radioactive byproducts.[11]

Lead-204, -207, and -208

[edit]

204Pb is entirely primordial, and is thus useful for estimating the fraction of the other lead isotopes in a given sample that are also primordial, since the relative fractions of the various primordial lead isotopes is constant everywhere.[12] Any excess lead-206, -207, and -208 is thus assumed to be radiogenic in origin,[12] allowing various uranium and thorium dating schemes to be used to estimate the age of rocks (time since their formation) based on the relative abundance of lead-204 to other isotopes. 207Pb is the end of the actinium series from 235U.

208Pb is the end of the thorium series from 232Th. While it only makes up approximately half of the composition of lead in most places on Earth, it can be found naturally enriched up to around 90% in thorium ores.[13] 208Pb is the heaviest known stable nuclide and also the heaviest known doubly magic nucleus, as Z = 82 and N = 126 correspond to closed nuclear shells.[14] As a consequence of this particularly stable configuration, its neutron capture cross section is very low (even lower than that of deuterium in the thermal spectrum), making it of interest for lead-cooled fast reactors.

In 2025 a published study suggested that the nucleus of 208Pb is not perfectly spherical as previously believed, but rather is a "prolate spheroid", more commonly described as the shape of a rugby ball.[15]

Lead-210

[edit]

Lead-210 (210Pb) is a radiogenic isotope of lead, found in the decay chain of uranium-238. It is a beta emitter with a half-life of 22.20 years. In addition to dating recent sediments, 210Pb is widely applied for studying soil erosion and sedimentation dynamics in agricultural and natural environments. The unsupported or excess component (210Pbex), derived from atmospheric fallout of radon-222 decay products, accumulates in surface soils and decays with a half-life of 22.3 years. Its depth-dependent activity profile enables reconstruction of soil redistribution over the past century.

Because 210Pb deposition is continuous and globally widespread, the method provides a long-term perspective that complements the medium-term records obtained from anthropogenic radionuclides such as 137Cs. It has been used to quantify erosion and deposition rates, assess land degradation, and evaluate soil conservation practices, offering valuable data for geomorphic and environmental research.[16]

Lead-212

[edit]

Lead-212 (212Pb) is a radioactive isotope of lead that has gained significant attention in nuclear medicine, particularly in targeted alpha therapy (TAT).[17] This isotope is part of the thorium decay series and serves as an important intermediate in various radioactive decay chains.[18] 212Pb is produced through the decay of radon-220 (220Rn), an intermediate product of thorium-228 (228Th) decay.[17] It undergoes radioactive decay through beta emission to form bismuth-212 (212Bi), which further decays to emit alpha particles.[19] This decay chain is particularly important in medical applications, as it is an in-vivo generator system of alpha particles, that can be utilized for therapeutic purposes, particularly TAT, by delivering potent, localized radiation to cancer cells.

The isotope is part of the thorium decay series, which begins with natural thorium-232. Its beta decay (10.627 hours) results in the formation of bismuth-212 (212Bi), which then emits alpha particles (6.1 MeV), crucial for the effectiveness of TAT in cancer treatment.[20]

While in aqueous solutions, free Pb2+ tends to hydrolyze under physiological pH conditions to form species like Pb(OH)+, which can impact its biodistribution if not properly chelated,[21] chelator-modified complexes have demonstrated high stability in saline and serum environments for extended periods (e.g., 24–72 hours), which is critical for therapeutic applications.[22]

Lead-212 can be synthesized through several methods, with generator-based production utilizing the decay of 228Th being the most common. This includes direct extraction from 228Th, 224Ra/212Pb generators, and 220Rn-based generation. Each of these methods has its own advantages and complexities. These various production routes cater to different industrial needs and regulatory considerations in the field of radioisotope production.[20]

See also

[edit]

Daughter products other than lead

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Isotopes of lead

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Lead (Pb), with 82, has four stable isotopes: ^{204}Pb, ^{206}Pb, ^{207}Pb, and ^{208}Pb, which occur naturally with relative abundances of 1.4%, 24.1%, 22.1%, and 52.4%, respectively. These isotopes define the of lead as 207.2(1). The atomic masses are 203.97 u for ^{204}Pb, 205.97 u for ^{206}Pb, 206.98 u for ^{207}Pb, and 207.98 u for ^{208}Pb. The average atomic mass, calculated as the weighted average Σ (abundance/100 × mass) = 207.22 u, closely aligns with the reported standard atomic weight of 207.2 u, with minor differences due to natural isotopic variability and rounding. Among them, ^{204}Pb is the only primordial isotope, formed during the early solar system, while ^{206}Pb, ^{207}Pb, and ^{208}Pb are radiogenic, produced as end-products of the decay chains of (half-life 4.47 × 10^9 years), (half-life 7.04 × 10^8 years), and (half-life 1.4 × 10^10 years), respectively. This radiogenic origin leads to variations in isotopic ratios, such as ^{206}Pb/^{204}Pb (typically 14.0–30.0), ^{207}Pb/^{204}Pb (15.0–17.0), and ^{208}Pb/^{204}Pb (35.0–50.0), which reflect geological processes and source materials. Lead also has numerous radioactive isotopes, with notable examples including ^{210}Pb (half-life 22.1 years), which is part of the and used for dating recent sediments and atmospheric deposits up to about 100 years old. Other short-lived radioactive isotopes, such as ^{211}Pb (half-life 36.1 minutes from ^{235}U chain), ^{212}Pb (half-life 10.64 hours from ^{232}Th chain), and ^{214}Pb (half-life 26.8 minutes from ^{238}U chain), play roles in natural and radiometric studies. These isotopes are widely applied in for tracing sources, deposits, and environmental , as well as in and , where stable isotopes like ^{208}Pb serve as targets for producing heavier elements. Anthropogenic activities, including and industrial emissions, have altered natural isotopic signatures in many environments.

Overview

General characteristics

Lead has an atomic number of 82, with all isotopes featuring 82 protons in the nucleus. Approximately 43 isotopes of lead are known, spanning mass numbers from 178 to 220. These isotopes exhibit a range of nuclear properties influenced by the structure of the . The stability of lead isotopes is particularly notable in the region near closed nuclear shells, known as , with Z = 82 for protons and N = 126 for neutrons. This shell closure enhances binding and reduces decay probability, resulting in four stable isotopes among the known ones. Nuclei close to these magic configurations, such as the doubly magic ^{208}Pb (Z = 82, N = 126), demonstrate exceptional stability compared to neighboring isotopes. Radioactive isotopes of lead heavier than the stable ones predominantly decay via alpha emission, while those lighter than the stable isotopes favor beta decay. The alpha decay process involves the emission of a helium-4 nucleus and can be represented by the general reaction: APb→A−4Hg+24He^{A}\mathrm{Pb} \to ^{A-4}\mathrm{Hg} + ^{4}_{2}\mathrm{He} Binding energy per nucleon in lead isotopes generally increases with mass number up to the region of maximum stability around A ≈ 208, reflecting the filling of nuclear shells, and then decreases for more neutron-rich or proton-deficient species. An odd-even staggering effect is observed in the binding energies, where even-even nuclei (even proton and neutron numbers) are more bound than adjacent odd-A nuclei due to enhanced pairing interactions between like nucleons. The concept of isotopes emerged in the early from observations of lead samples with varying atomic weights derived from different radioactive decay chains, such as those of and . , developed in the 1910s by J.J. Thomson and refined by F.W. Aston, provided the first direct confirmation of multiple lead isotopes by separating ions based on mass-to-charge ratios.

Natural occurrence and abundance

Lead occurs naturally on primarily through its four isotopes, which constitute the bulk of terrestrial lead in the crust, ores, and environmental samples. In standard terrestrial lead, the approximate isotopic abundances are 1.4% for 204^{204}Pb, 24.1% for 206^{206}Pb, 22.1% for 207^{207}Pb, and 52.4% for 208^{208}Pb. These values represent average compositions derived from bulk measurements and are used as references in geochemical analyses. The isotope 204^{204}Pb is non-radiogenic and primordial, originating from the early solar system without subsequent production from radioactive decay, whereas 206^{206}Pb, 207^{207}Pb, and 208^{208}Pb accumulate as stable end-products from the decay of uranium (238^{238}U to 206^{206}Pb and 235^{235}U to 207^{207}Pb) and thorium (232^{232}Th to 208^{208}Pb) isotopes over billions of years. Geological processes, including magma differentiation, hydrothermal fluid circulation, and sedimentation, lead to variations in these abundances across different rock types and ore deposits. For instance, in galena (PbS) ores, isotopic ratios such as 206^{206}Pb/204^{204}Pb can range from 15.3 to 18.7, reflecting source rock ages and mixing histories. Cosmically, lead isotopes arise from , with significant contributions from the in low-mass stars during helium shell burning and the r-process in explosive events like mergers. 208^{208}Pb is predominantly produced via the (about 80-90% of its solar abundance), while 206^{206}Pb has a larger r-process component (roughly 50%), and 207^{207}Pb shows mixed origins; 204^{204}Pb traces back to earlier p-process or primordial . These processes explain the observed solar system abundances, where lead's total cosmic prevalence is low, around 3 atoms per million atoms. Precise determination of natural lead isotopic abundances and ratios relies on thermal ionization mass spectrometry (TIMS), a technique that ionizes lead samples on a heated filament and measures currents for high-precision ratio analysis, often achieving uncertainties below 0.01%. TIMS remains the gold standard for such measurements due to its sensitivity and accuracy in handling small sample sizes from geological materials.

Stable Isotopes

Lead-204

Lead-204 (²⁰⁴Pb) is the only , non-radiogenic of lead, possessing a of 204, an of 82, and a number of 122. As an even-even nucleus with 82 protons and 122 s, it exhibits a nuclear spin of 0 and is fully , with no observed radioactive decay and an estimated exceeding 1.4 × 10¹⁷ years. Its high , approximately 1,607,520 keV total or 7.877 MeV per , contributes to this exceptional stability among heavy isotopes. ²⁰⁴Pb originated as a formed through approximately 4.6 billion years ago, prior to the formation of the solar system, primarily via the slow process (s-process) in stars. Unlike the other stable lead isotopes, it is not produced by within the solar system, making it a direct remnant of the from which the solar system condensed. In natural lead, ²⁰⁴Pb constitutes about 1.4% of the isotopic abundance, a low proportion that underscores its utility as a reference for quantifying radiogenic contributions from and decay. Isotopic ratios such as ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb are routinely normalized to ²⁰⁴Pb in geochronological studies to distinguish primordial lead from radiogenic additions, enabling precise age determinations via lead-lead methods. This non-radiogenic signature of ²⁰⁴Pb is particularly valuable for identifying uncontaminated primordial lead in , such as meteorites, and in ancient terrestrial samples from Earth's early crust. For instance, analyses of phases in iron meteorites like Canyon Diablo have used ²⁰⁴Pb ratios to establish baseline compositions, confirming the age of the solar system at around 4.55 billion years and revealing minimal radiogenic evolution in these primitive objects.

Lead-206, Lead-207, and Lead-208

Lead-206 is the stable end-product of the , which has an overall of approximately 4.468 billion years. In natural lead, it constitutes about 24.1% of the isotopic abundance. As an even-even nucleus with 82 protons and 124 neutrons, lead-206 has a nuclear spin of 0 and is entirely against further decay. Lead-207 forms as the stable terminus of the , characterized by a of roughly 704 million years. It accounts for approximately 22.1% of natural lead's isotopic composition. Like lead-206, lead-207 is an even-even with nuclear spin 0, featuring 82 protons and 125 neutrons, and plays a key role in uranium-lead (U-Pb) for dating ancient materials. Lead-208 arises from the , with a of about 14.05 billion years. It dominates natural lead at around 52.4% abundance. This even-even nucleus, possessing 82 protons and 126 s, also has a nuclear spin of 0 and exhibits the highest neutron excess among stable lead isotopes, contributing to its closed-shell structure and exceptional stability. These three isotopes are radiogenic, accumulating over geological time relative to the primordial lead-204 isotope. Their interconnections are evident in the ratios ^{206}Pb/^{204}Pb, ^{207}Pb/^{204}Pb, and ^{208}Pb/^{204}Pb, which serve as isotopic "clocks" for determining of the and meteorites through lead-lead dating methods. These ratios reflect the differential decay rates of their parent nuclides, enabling precise geochronological reconstructions of planetary formation.

Radioactive Isotopes

Isotopes in decay chains

The radioactive isotopes of lead play crucial roles as intermediate members in the three principal natural decay series: the (4n+2) chain, the (4n) chain, and the (4n+3, or ) series. These chains originate from long-lived primordial actinides and proceed through a sequence of alpha and beta decays, ultimately terminating at lead isotopes. The lead nuclides in these series are produced via of preceding or parents and themselves decay primarily by beta emission, with half-lives ranging from minutes to years that influence their transient accumulation in environmental systems. In the , which begins with the of 238U^{238}\mathrm{U} ( 4.468 billion years) and includes intermediates such as 226Ra^{226}\mathrm{Ra}, 222Rn^{222}\mathrm{Rn}, and 218Po^{218}\mathrm{Po}, two prominent lead isotopes appear. The first is 214Pb^{214}\mathrm{Pb}, formed by the of 218Po^{218}\mathrm{Po}, with a of 26.8 minutes and undergoing 100% beta-minus decay to 214Bi^{214}\mathrm{Bi}. Its decay proceeds via the equation 214Pb→214Bi+e−+νˉe^{214}\mathrm{Pb} \to ^{214}\mathrm{Bi} + e^- + \bar{\nu}_e with a Q-value of 1.019 MeV; no significant branching to other modes occurs. Further along the chain, 210Pb^{210}\mathrm{Pb} is produced by the of 214Po^{214}\mathrm{Po} and has a of 22.3 years, decaying 100% by beta-minus emission to 210Bi^{210}\mathrm{Bi}, following 210Pb→210Bi+e−+νˉe^{210}\mathrm{Pb} \to ^{210}\mathrm{Bi} + e^- + \bar{\nu}_e (Q-value 0.0635 MeV). This longer-lived isotope allows for measurable ingrowth and supports secular equilibrium in uranium-rich matrices, though its environmental mobility is enhanced by the gaseous 222Rn^{222}\mathrm{Rn} precursor, facilitating atmospheric transport and deposition in soils and sediments. The chain, starting from 232Th^{232}\mathrm{Th} ( 14.05 billion years) and featuring intermediates like 228Ra^{228}\mathrm{Ra}, 220Rn^{220}\mathrm{Rn}, and 216Po^{216}\mathrm{Po}, includes 212Pb^{212}\mathrm{Pb} as its key lead isotope. Formed by the of 216Po^{216}\mathrm{Po}, 212Pb^{212}\mathrm{Pb} of 10.64 hours and decays exclusively (100% branching ) by beta-minus to 212Bi^{212}\mathrm{Bi}, with 212Pb→212Bi+e−+νˉe^{212}\mathrm{Pb} \to ^{212}\mathrm{Bi} + e^- + \bar{\nu}_e (Q-value 0.570 MeV). Its relatively short limits accumulation compared to 210Pb^{210}\mathrm{Pb}, but in thorium-bearing minerals, it contributes to chain equilibrium, with moderate geochemical mobility influenced by and organic complexation. In the uranium-235 actinium series, initiated by 235U^{235}\mathrm{U} (half-life 703.8 million years) and proceeding through 231Pa^{231}\mathrm{Pa}, 227Ac^{227}\mathrm{Ac}, 219Rn^{219}\mathrm{Rn}, and 215Po^{215}\mathrm{Po}, the lead isotope is 211Pb^{211}\mathrm{Pb}, resulting from the alpha decay of 215Po^{215}\mathrm{Po}. It possesses a half-life of 36.1 minutes and decays 100% by beta-minus to 211Bi^{211}\mathrm{Bi}, as described by 211Pb→211Bi+e−+νˉe^{211}\mathrm{Pb} \to ^{211}\mathrm{Bi} + e^- + \bar{\nu}_e (Q-value 1.367 MeV), with no notable alternative decay branches. Due to its brief persistence, 211Pb^{211}\mathrm{Pb} rarely achieves disequilibrium outside closed systems, but its position underscores the chain's role in tracing uranium fractionation in geological processes.
Decay ChainLead IsotopeHalf-LifeDecay Mode (Branching Ratio)Successor
Uranium-238214Pb^{214}\mathrm{Pb}26.8 minβ⁻ (100%)214Bi^{214}\mathrm{Bi}
Uranium-238210Pb^{210}\mathrm{Pb}22.3 yβ⁻ (100%)210Bi^{210}\mathrm{Bi}
Thorium-232212Pb^{212}\mathrm{Pb}10.64 hβ⁻ (100%)212Bi^{212}\mathrm{Bi}
Uranium-235211Pb^{211}\mathrm{Pb}36.1 minβ⁻ (100%)211Bi^{211}\mathrm{Bi}
These lead isotopes exhibit varying degrees of mobility within their chains, often higher than their parents due to lead's as Pb(II) in aqueous environments, which affects dispersal in and soils.

Other notable radioactive isotopes

Lead-202 is the longest-lived radioactive of lead outside the natural decay chains, with a of approximately 53,000 years. It primarily decays via to thallium-202, with a minor branch to mercury-198. This is synthetic and produced through reactions on stable lead isotopes in nuclear reactors or via in particle accelerators. Due to its even-even nuclear structure, lead-202 has been considered in theoretical studies of processes, though no such decay has been observed. Lead-205, with a half-life of 17.3 million years, decays exclusively by electron capture to thallium-205. It occurs in trace amounts naturally but is predominantly produced synthetically, often through neutron capture on lead-204 in reactors or spallation reactions in high-energy proton accelerators. In astrophysics, lead-205 serves as a key tracer for the slow neutron capture process (s-process) in asymptotic giant branch stars, enabling chronometric studies of nucleosynthesis and the early solar system's formation timeline. Recent measurements of its decay properties have refined isolation times for s-process material in presolar grains, supporting models of galactic chemical evolution. Shorter-lived radioactive isotopes of lead, such as lead-203 (half-life 2.16 days, electron capture to thallium-203) and lead-201 (half-life 9.33 hours, electron capture to thallium-201), are produced primarily in cyclotrons or linear accelerators via proton or deuteron bombardment of thallium or bismuth targets. These isotopes find applications in nuclear medicine for imaging and therapy due to their suitable decay energies and short half-lives.

Applications

Geochronology and geochemistry

Lead isotopes play a central role in through the uranium-lead (U-Pb) dating method, which exploits the decay of isotopes to radiogenic lead. The primary chains involve ^{238}U decaying to ^{206}Pb and ^{235}U to ^{207}Pb, allowing ages to be calculated from the ratios ^{206}Pb/^{238}U and ^{207}Pb/^{235}U. For a without initial lead, the age tt of a sample is given by the equation: t=1λln⁡(1+206Pb238U)t = \frac{1}{\lambda} \ln \left(1 + \frac{^{206}\mathrm{Pb}}{^{238}\mathrm{U}}\right) where λ\lambda is the decay constant of ^{238}U (approximately 1.55125 \times 10^{-10} yr^{-1}). This method is particularly robust when plotted on a concordia diagram, which displays ^{207}Pb/^{235}U versus ^{206}Pb/^{238}U; concordant points lie on a curve representing simultaneous ages from both decay chains, enabling detection of lead loss or gain events that cause discordance. Complementing U-Pb, thorium-lead (Th-Pb) dating utilizes the decay of ^{232}Th to ^{208}Pb, providing an additional chronometer for systems with measurable thorium. The ^{208}Pb/^{232}Th ratio is especially useful in minerals with initial lead contamination, as it offers independent age constraints when integrated with U-Pb data on a combined . This approach enhances resolution in complex geological settings, such as those involving common lead. Applications of these methods include zircon crystals, which incorporate uranium during crystallization and resist post-formation alteration, yielding ages up to 4.4 Ga for the oldest terrestrial materials and contributing to the established age of 4.54 Ga when combined with meteoritic data. U-Pb of accessory minerals in ore deposits, such as or carbonates, constrains mineralization events, for example, sandstone-hosted Pb-Zn deposits to the or iron oxide copper-gold systems to the . In , lead isotope ratios serve as tracers for environmental processes, particularly anthropogenic . The ^{206}Pb/^{207}Pb ratio distinguishes industrial sources, such as leaded gasoline (typically 1.06–1.09) from natural crustal lead (around 1.20), allowing reconstruction of pollution histories in ice cores and sediments. For instance, analyses of Tibetan ice cores reveal elevated lead from ancient since 400 BCE and modern industrial inputs peaking in the , while sediment cores from lakes track shifts from to emissions over the past century. These ratios enable source apportionment, quantifying contributions from , , and atmospheric deposition. Recent advances in the have improved U-Pb through ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), enabling in-situ microanalysis of minerals like and carbonates at spatial resolutions of 10–50 μm without chemical preparation. This technique facilitates high-throughput dating of complex samples, such as detrital grains in sediments or zoned minerals, reducing in age populations and revealing intra-grain variations from metamorphic events. LA-ICP-MS has been pivotal in refining timelines for formation and pollution dispersal, with protocols now standard for achieving <1% precision on ^{206}Pb/^{238}U ratios in young samples.

Nuclear physics and other uses

Lead-208 serves as a key target material in experiments aimed at probing exotic nuclei and nuclear shell structures. As the heaviest known doubly nucleus, with closed proton and shells at =82 and N=126, it provides a stable reference for studying with relativistic radioactive beams. At the Facility for Antiproton and Ion Research (), 208Pb targets are employed in high-energy fragmentation and to investigate shell closures beyond the line of stability, enabling precise measurements of nuclear densities and excitation modes in neutron-rich isotopes. Theoretical and experimental efforts have explored 208Pb in the context of processes, leveraging its role as a core in shell-model calculations for matrix elements relevant to candidates. While 208Pb itself is stable, searches for rare decays in related systems, including limits from low-background setups similar to GERDA, have established bounds exceeding 10^{20} years for associated processes, informing mass constraints. In medical applications, the radioactive 212Pb, with a of 10.6 hours, functions as an alpha-particle emitter in targeted for cancer treatment. It decays through a that delivers high-energy alpha to tumor cells while minimizing damage to surrounding tissue, particularly when conjugated to chelators like DOTAM for specific targeting of receptors overexpressed in malignancies such as neuroendocrine tumors. Preclinical and early clinical studies with 212Pb-DOTAMTATE have demonstrated promising antitumor efficacy and favorable dosimetry in somatostatin receptor-positive cancers. Phase 2 clinical trials as of October 2025 have shown that 212Pb-DOTAMTATE achieved all primary efficacy endpoints, with durable responses in patients with advanced gastroenteropancreatic neuroendocrine tumors. Enriched 208Pb is utilized in low-background due to its lack of long-lived radioactive contaminants in the and decay chains, enabling ultrasensitive detection of faint signals. This purity reduces intrinsic background from beta and gamma emissions, making it ideal for shielding and detector components in precision measurements of environmental or . Additionally, 210Pb, produced in the atmosphere primarily through the decay of 222Rn emanating from the , serves as a tracer for atmospheric fallout and dynamics. Its global production rate is approximately 1-2 × 10^4 atoms m^{-2} s^{-1}, with latitudinal and seasonal variations, allowing tracking of particle deposition fluxes and residence times, as evidenced by long-term monitoring datasets correlating 210Pb with seasonal patterns and .

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