Astatine-205

Properties and data of the isotope ²⁰⁵At.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

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

General data

Name of the isotope:Astatine-205; At-205Symbol:²⁰⁵At or 20585AtMass number A:205 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:120Isotopic mass:204.986074(16) u (atomic weight of Astatine-205)Nuclide mass:204.9394503 u (calculated nuclear mass without electrons)Mass excess:-12.97199 MeVMass defect:1.71884364 u (per nucleus)Nuclear binding energy:1601.0925376 MeV (per nucleus)
7.8102075 MeV (average binding energy per nucleon)Separation energy:S_N = 9.168(27) MeV (first neutron)
S_P = 1.920(19) MeV (first proton)Half-life:26.9(8) minDecay constant λ:0.00042945921967779 s^-1Specific activity α:1.267776428675 × 10⁺¹⁸ Bq g^-1
34264227.802043 Ci g^-1Spin and parity:
(nuclear angular momentum)9/2-Year of discovery:1951

Radioactive Decay

Half-life T_½ = 26.9(8) min (minutes) respectively 1.614 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰¹Bi	10(2) %	6.0196(17) MeV
EC/β⁺	²⁰⁵Po	90(2) %	4.549(18) MeV

Parent Nuclides

Direct parent isotopes are: ²⁰⁹Fr, ²⁰⁵Rn.

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
^205mAt	2339.65(23) keV	7.76(14) μs	29/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 120) and isobaric (same nucleon number A = 205) with Astatine-205. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 120	Isobar A = 205
73	¹⁹³Ta
74	¹⁹⁴W
75	¹⁹⁵Re
76	¹⁹⁶Os
77	¹⁹⁷Ir	²⁰⁵Ir
78	¹⁹⁸Pt	²⁰⁵Pt
79	¹⁹⁹Au	²⁰⁵Au
80	²⁰⁰Hg	²⁰⁵Hg
81	²⁰¹Tl	²⁰⁵Tl
82	²⁰²Pb	²⁰⁵Pb
83	²⁰³Bi	²⁰⁵Bi
84	²⁰⁴Po	²⁰⁵Po
85	²⁰⁵At	²⁰⁵At
86	²⁰⁶Rn	²⁰⁵Rn
87	²⁰⁷Fr	²⁰⁵Fr
88	²⁰⁸Ra	²⁰⁵Ra
89	²⁰⁹Ac	²⁰⁵Ac
90	²¹⁰Th