Astatine-204m

Properties and data of the isotope ²⁰⁴At.

Content

General data

Name of the isotope:Astatine-204m; At-204mSymbol:²⁰⁴At or 20485AtMass number A:204 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:119Isotopic mass:203.987251(24) u (atomic weight of Astatine-204m)
Excitation energy: 587.3(2) keVNuclide mass:203.9406273 u (calculated nuclear mass without electrons)Mass excess:-11.87562 MeVMass defect:1.709001724 u (per nucleus)Nuclear binding energy:1591.9248519 MeV (per nucleus)
7.8035532 MeV (average binding energy per nucleon)Half-life:108(10) msDecay constant λ:6.4180294496291 s^-1Specific activity α:1.903954551176 × 10⁺²² Bq g^-1
514582311128.86 Ci g^-1Spin and parity:
(nuclear angular momentum)10-

Radioactive Decay

Half-life T_½ = 108(10) ms respectively 1.08 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	²⁰⁴At	100 %

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
²⁰⁴At		9.12(11) min	7+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 119) and isobaric (same nucleon number A = 204) with Astatine-204m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

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