Thorium-209

Properties and data of the isotope ²⁰⁹Th.

Content

General data

Name of the isotope:Thorium-209; Th-209Symbol:²⁰⁹Th or 20990ThMass number A:209 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:119Isotopic mass:209.01757(15) u (atomic weight of Thorium-209)Nuclide mass:208.9682042 u (calculated nuclear mass without electrons)Mass excess:16.36635 MeVMass defect:1.717807884 u (per nucleus)Nuclear binding energy:1600.1277371 MeV (per nucleus)
7.65611357 MeV (average binding energy per nucleon)Separation energy:S_N = 8.39(14) MeV (first neutron)
S_P = 1.67(15) MeV (first proton)Half-life:2.5 msDecay constant λ:277.25887222398 s^-1Specific activity α:7.988956857416 × 10⁺²³ Bq g^-1
21591775290314 Ci g^-1Spin and parity:
(nuclear angular momentum)(13/2+)Year of discovery:1996

Radioactive Decay

Half-life T_½ = 2.5 ms respectively 2.5 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰⁵Ra		8.10(14) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 119) and isobaric (same nucleon number A = 209) with Thorium-209. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 119	Isobar A = 209
73	¹⁹²Ta
74	¹⁹³W
75	¹⁹⁴Re
76	¹⁹⁵Os
77	¹⁹⁶Ir
78	¹⁹⁷Pt
79	¹⁹⁸Au	²⁰⁹Au
80	¹⁹⁹Hg	²⁰⁹Hg
81	²⁰⁰Tl	²⁰⁹Tl
82	²⁰¹Pb	²⁰⁹Pb
83	²⁰²Bi	²⁰⁹Bi
84	²⁰³Po	²⁰⁹Po
85	²⁰⁴At	²⁰⁹At
86	²⁰⁵Rn	²⁰⁹Rn
87	²⁰⁶Fr	²⁰⁹Fr
88	²⁰⁷Ra	²⁰⁹Ra
89	²⁰⁸Ac	²⁰⁹Ac
90	²⁰⁹Th	²⁰⁹Th