Actinium-211

Properties and data of the isotope ²¹¹Ac.

Contents

Actinium-211 is a radioisotope of the chemical element actinium, which, in addition to element-specific 89 protons, has 122 neutrons in the atomic nucleus, resulting in the mass number 211. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ²¹¹Ac is for academic purposes only.

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

General data

Name of the isotope:Actinium-211; Ac-211Symbol:²¹¹Ac or 21189AcMass number A:211 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:122Isotopic mass:211.00773(6) u (atomic weight of Actinium-211)Nuclide mass:210.9589126 u (calculated nuclear mass without electrons)Mass excess:7.20045 MeVMass defect:1.7458176 u (per nucleus)Nuclear binding energy:1626.21861949 MeV (per nucleus)
7.70719725 MeV (average binding energy per nucleon)Separation energy:S_N = 9.66(8) MeV (first neutron)
S_P = 0.53(5) MeV (first proton)Half-life:0.21(3) sDecay constant λ:3.3007008598093 s^-1Specific activity α:9.420514461746 × 10⁺²¹ Bq g^-1
254608498966.13 Ci g^-1Spin and parity:
(nuclear angular momentum)9/2-Year of discovery:1968

Radioactive Decay

Half-life T_½ = 0.21(3) s respectively 2.1 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰⁷Fr	> 99.8 %	7.62(5) MeV
EC/β⁺	²¹¹Ra	< 0.2 %	6.37(5) MeV

Parent Nuclides

Direct parent isotopes are: ²¹⁵Pa, ²¹¹Th.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 122) and isobaric (same nucleon number A = 211) with Actinium-211. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 122	Isobar A = 211
74	¹⁹⁶W
75	¹⁹⁷Re
76	¹⁹⁸Os
77	¹⁹⁹Ir
78	²⁰⁰Pt
79	²⁰¹Au
80	²⁰²Hg	²¹¹Hg
81	²⁰³Tl	²¹¹Tl
82	²⁰⁴Pb	²¹¹Pb
83	²⁰⁵Bi	²¹¹Bi
84	²⁰⁶Po	²¹¹Po
85	²⁰⁷At	²¹¹At
86	²⁰⁸Rn	²¹¹Rn
87	²⁰⁹Fr	²¹¹Fr
88	²¹⁰Ra	²¹¹Ra
89	²¹¹Ac	²¹¹Ac
90	²¹²Th	²¹¹Th
91	²¹³Pa
92	²¹⁴U