Lead-209

Properties and data of the isotope ²⁰⁹Pb.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Lead-209 is a radioisotope of the chemical element lead, which has 127 neutrons in its atomic nucleus in addition to the element-specific 82 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 209. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²⁰⁹Pb is exclusively for academic purposes and experimental research.

In 1940, a research report was published that first described evidence of the short-lived isotope lead-209. According to the investigations described therein, a 9 MeV deuteron beam from the Cavendish cyclotron struck a mercury sample. After chemical separation and subsequent recording of the activity with a Geiger counter and a thyratron counter, a distinct radiation component was isolated, the half-life of which was determined to be approximately 2.75 hours. The analysis of this radioactive decay product led to the unambiguous identification of the previously unknown isotope lead-209 [1].

See also: List of individual Lead isotopes (and general data sources).

General data

Name of the isotope:Lead-209; Pb-209Symbol:²⁰⁹Pb or 20982PbMass number A:209 (= number of nucleons)Atomic number Z:82 (= number of protons)Neutrons N:127Isotopic mass:208.9810900(19) u (atomic weight of Lead-209)Nuclide mass:208.9361116 u (calculated nuclear mass without electrons)Mass excess:-17.61455 MeVMass defect:1.761006956 u (per nucleus)Nuclear binding energy:1640.36741347 MeV (per nucleus)
7.84864791 MeV (average binding energy per nucleon)Separation energy:S_N = 3.9374(13) MeV (first neutron)
S_P = 8.1534(21) MeV (first proton)Half-life:3.235(5) hDecay constant λ:5.951804744632 × 10^-5 s^-1Specific activity α:1.723202237645 × 10⁺¹⁷ Bq g^-1
4657303.3449868 Ci g^-1Spin and parity:
(nuclear angular momentum)9/2+Magnetic dipole moment:μ(μ_N) = - 1.4735(16)Quadrupole moment Q:-0.269(165) barn (100 fm²)Nuclear g-factor:g_l = -0.32744444444444Charge radius:5.5100(14) femtometer fmYear of discovery:1940

Radioactive Decay

Half-life T_½ = 3.235(5) h (hours) respectively 1.1646 × 10⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	Details	γ energy (intensity)
β^-	²⁰⁹Bi	100 %	0.6440(11) MeV	Neutrino: 0.4473(14) MeV α: 0.1975(4) MeV

Parent Nuclides

Direct parent isotopes are: ²⁰⁹Tl, ²¹³Po, ²²³Ra, ²³²U, ²³³U.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 127) and isobaric (same nucleon number A = 209) with Lead-209. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 127	Isobar A = 209
76	²⁰³Os
77	²⁰⁴Ir
78	²⁰⁵Pt
79	²⁰⁶Au	²⁰⁹Au
80	²⁰⁷Hg	²⁰⁹Hg
81	²⁰⁸Tl	²⁰⁹Tl
82	²⁰⁹Pb	²⁰⁹Pb
83	²¹⁰Bi	²⁰⁹Bi
84	²¹¹Po	²⁰⁹Po
85	²¹²At	²⁰⁹At
86	²¹³Rn	²⁰⁹Rn
87	²¹⁴Fr	²⁰⁹Fr
88	²¹⁵Ra	²⁰⁹Ra
89	²¹⁶Ac	²⁰⁹Ac
90	²¹⁷Th	²⁰⁹Th
91	²¹⁸Pa
92	²¹⁹U
93	²²⁰Np

External data and identifiers

Adopted Levels, Gammas:NuDat 209Pb

Literature and References

[1] - K. A. Hofmann, E. Strauss:
Radioactives Blei und radioactive seltene Erden.
In: Berichte der deutschen chemischen Gesellschaft, 33, 3, (1900), DOI 10.1002/cber.19000330364.