Lead-205

Properties and data of the isotope ²⁰⁵Pb.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Lead-205 is a radioisotope of the chemical element lead, which has 123 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 205. There are no practical technical applications for the nuclide ²⁰⁵Pb.

In 1954, a report was published in which the long-lived isotope lead-205 was described for the first time. In the experiments presented there, thallium samples were irradiated with 21-MeV deuterons (hydrogen-2 nuclei) from a cyclotron, after which chemical processing provided lead isotopes for mass-spectrometric analysis. Examination of the irradiated material with a mass spectrometer revealed an activity that could be unambiguously assigned to the isotope lead-205 [1].

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

General data

Name of the isotope:Lead-205; Pb-205Symbol:²⁰⁵Pb or 20582PbMass number A:205 (= number of nucleons)Atomic number Z:82 (= number of protons)Neutrons N:123Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.5 (= neutron-proton ratio)Neutron excess (N-Z):41Isotopic mass:204.9744817(12) u (atomic weight of Lead-205)Nuclide mass:204.9295033 u (calculated nuclear mass without electrons)Mass excess:-23.77014 MeVMass defect:1.732955592 u (per nucleus)Nuclear binding energy:1614.23773621 MeV (per nucleus)
7.87433042 MeV (average binding energy per nucleon)Separation energy:S_N = 6.73167(11) MeV (first neutron)
S_P = 6.71306(21) MeV (first proton)Half-life:1.70(9) × 10⁷aDecay constant λ:1.292057521546 × 10^-15 s^-1Specific activity α:3814192.3499472 Bq g^-1
0.0001030862797283 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2-Magnetic dipole moment:μ(μ_N) = +0.7117(4)Quadrupole moment Q:+2.26(37) barn (100 fm²)Nuclear g-factor:g_l = 0.28468Charge radius:5.4828(15) femtometer fmYear of discovery:1954

Radioactive Decay

Half-life T_½ = 1.70(9) × 10⁷a respectively 5.36467741568064 × 10¹⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC	²⁰⁵Tl	100 %	0.0506(17) MeV

Parent Nuclides

Direct parent isotopes are: ²⁰⁵Bi, ²⁰⁹Po.

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
^205m2Pb	1013.85(3) keV	5.55(2) ms	13/2+
^205m1Pb	2.329(7) keV	24.2(4) μs	1/2-
^205m3Pb	3195.7(5) keV	217(5) ns	25/2-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 123) and isobaric (same nucleon number A = 205) with Lead-205. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 123	Isobar A = 205
74	¹⁹⁷W
75	¹⁹⁸Re
76	¹⁹⁹Os
77	²⁰⁰Ir	²⁰⁵Ir
78	²⁰¹Pt	²⁰⁵Pt
79	²⁰²Au	²⁰⁵Au
80	²⁰³Hg	²⁰⁵Hg
81	²⁰⁴Tl	²⁰⁵Tl
82	²⁰⁵Pb	²⁰⁵Pb
83	²⁰⁶Bi	²⁰⁵Bi
84	²⁰⁷Po	²⁰⁵Po
85	²⁰⁸At	²⁰⁵At
86	²⁰⁹Rn	²⁰⁵Rn
87	²¹⁰Fr	²⁰⁵Fr
88	²¹¹Ra	²⁰⁵Ra
89	²¹²Ac	²⁰⁵Ac
90	²¹³Th
91	²¹⁴Pa
92	²¹⁵U