Astatine-209m

Properties and data of the isotope ^209mAt.

Contents

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

General data

Name of the isotope:Astatine-209m; At-209mSymbol:^209mAt or 209m85AtMass number A:209 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:124Isotopic mass:208.986170(5) u (atomic weight of Astatine-209m)
Excitation energy: 2429.32(22) keVNuclide mass:208.9395463 u (calculated nuclear mass without electrons)Mass excess:-12.88256 MeVMass defect:1.753407304 u (per nucleus)Nuclear binding energy:1633.28838323 MeV (per nucleus)
7.81477695 MeV (average binding energy per nucleon)Half-life:0.916(10) μsDecay constant λ:756710.8958078 s^-1Specific activity α:2.190874810001 × 10⁺²⁷ Bq g^-1
5.921283270274 × 10⁺¹⁶ Ci g^-1Spin and parity:
(nuclear angular momentum)29/2+Magnetic dipole moment:μ(μ_N) = 15.38(14)Quadrupole moment Q:1.50(15) barn (100 fm²)Nuclear g-factor:g_l = 1.0606896551724

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
²⁰⁹At		5.42(5) h	9/2-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 124) and isobaric (same nucleon number A = 209) with Astatine-209m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 124	Isobar A = 209
75	¹⁹⁹Re
76	²⁰⁰Os
77	²⁰¹Ir
78	²⁰²Pt
79	²⁰³Au	²⁰⁹Au
80	²⁰⁴Hg	²⁰⁹Hg
81	²⁰⁵Tl	²⁰⁹Tl
82	²⁰⁶Pb	²⁰⁹Pb
83	²⁰⁷Bi	²⁰⁹Bi
84	²⁰⁸Po	²⁰⁹Po
85	²⁰⁹At	²⁰⁹At
86	²¹⁰Rn	²⁰⁹Rn
87	²¹¹Fr	²⁰⁹Fr
88	²¹²Ra	²⁰⁹Ra
89	²¹³Ac	²⁰⁹Ac
90	²¹⁴Th	²⁰⁹Th
91	²¹⁵Pa
92	²¹⁶U