Lead-208

Properties and data of the isotope ²⁰⁸Pb.

Contents

Lead-208 is the heaviest stable and therefore non-radioactive isotope of the chemical element lead with the mass number 208. It is also the heaviest known stable isotope of an element at all and with Z = 82 and N = 126 has the heaviest known doubly magic atomic nucleus (closed nuclear shells). As a result of this particularly stable configuration of the nuclide, the thermal neutron capture cross-section (230 ± 12 μb) is very small. Pb-208 is therefore suitable as a coolant and neutron moderator in nuclear reactors.

General data

Name of the isotope:Lead-208; Pb-208Other names:Thorium DSymbol:²⁰⁸Pb or 20882PbMass number A:208 (= number of nucleons)Atomic number Z:82 (= number of protons)Neutrons N:126Isotopic mass:207.976653(8) u (atomic weight of Lead-208)Nuclide mass:207.9316746 u (calculated nuclear mass without electrons)Mass excess:-21.74759 MeVMass defect:1.75677904 u (per nucleus)Nuclear binding energy:1636.42913509 MeV (per nucleus)
7.86744776 MeV (average binding energy per nucleon)Separation energy:S_N = 7.36787(5) MeV (first neutron)
S_P = 8.003(5) MeV (first proton)Half-life:stableSpin and parity:
(nuclear angular momentum)0+Charge radius:5.5012(13) femtometer fmYear of discovery:1927

Parent Nuclides

Direct parent isotopes are: ²⁰⁸Bi, ²¹²Po, ²⁰⁸Tl, ²²²Ra, ²²⁸Th, ²⁴²Cm.

Occurrence

Ordinary deposits of lead and elemental lead extracted from them, as well as lead compounds, contain the element in the isotopic composition shown below. Exceptions are uranium and thorium ores or certain minerals. For example, lead-208 is a stable, radiogenic end product of the thorium decay chain (see Figure 1) and occurs in the corresponding materials in a concentration of 88.34% - based on the total lead contained therein.

Comparison of the natural Lead isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Lead Isotopic mixture	207.2 u	100 %
Isotope ²⁰⁴Pb	203.973044(8) u	1.4(6) %	1.4 × 10¹⁷ a	0+
Isotope ²⁰⁶Pb	205.974466(8) u	24.1(30) %	stable	0+
Isotope ²⁰⁷Pb	206.975897(8) u	22.1(50) %	stable	1/2-
Isotope ²⁰⁸Pb	207.976653(8) u	52.4(70) %	stable	0+

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^208mPb	4895.23(5) keV	0.50(5) μs	10+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 126) and isobaric (same nucleon number A = 208) with Lead-208. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 126	Isobar A = 208
76	²⁰²Os
77	²⁰³Ir
78	²⁰⁴Pt	²⁰⁸Pt
79	²⁰⁵Au	²⁰⁸Au
80	²⁰⁶Hg	²⁰⁸Hg
81	²⁰⁷Tl	²⁰⁸Tl
82	²⁰⁸Pb	²⁰⁸Pb
83	²⁰⁹Bi	²⁰⁸Bi
84	²¹⁰Po	²⁰⁸Po
85	²¹¹At	²⁰⁸At
86	²¹²Rn	²⁰⁸Rn
87	²¹³Fr	²⁰⁸Fr
88	²¹⁴Ra	²⁰⁸Ra
89	²¹⁵Ac	²⁰⁸Ac
90	²¹⁶Th	²⁰⁸Th
91	²¹⁷Pa
92	²¹⁸U
93	²¹⁹Np

External data and identifiers

CAS:13966-28-4InChI Key:WABPQHHGFIMREM-OUBTZVSYSA-NInChI Code:1S/Pb/i1+1SMILES:[208Pb]PubChem:ID 6335509Adopted Levels, Gammas:NuDat 208Pb

Literature and References

[1] - J. C. Blackmon, S. Raman, J. K. Dickens, R. M. Lindstrom, R. L. Paul, J. E. Lynn:
Thermal-neutron capture by ²⁰⁸Pb.
In: Physical Review C, (2002), DOI 10.1103/PhysRevC.65.045801.

[2] - A. N. Shmelev et al.:
Radiogenic Lead with Dominant Content of ²⁰⁸Pb: New Coolant and Neutron Moderator for Innovative Nuclear Facilities.
In: Science and Technology of Nuclear Installations, (2011), DOI 10.1155/2011/252903.