Actinium-220

Properties and data of the isotope ²²⁰Ac.

Content

Actinium-220 is a radioisotope of the chemical element actinium, which, in addition to the element-specific 89 protons, has 131 neutrons in the atomic nucleus, resulting in the mass number 220. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ²²⁰Ac is for academic purposes only.

General data

Name of the isotope:Actinium-220; Ac-220Symbol:²²⁰Ac or 22089AcMass number A:220 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:131Isotopic mass:220.014754(7) u (atomic weight of Actinium-220)Nuclide mass:219.9659366 u (calculated nuclear mass without electrons)Mass excess:13.74326 MeVMass defect:1.816777844 u (per nucleus)Nuclear binding energy:1692.31766102 MeV (per nucleus)
7.692353 MeV (average binding energy per nucleon)Separation energy:S_N = 5.90(5) MeV (first neutron)
S_P = 2.94(1) MeV (first proton)Half-life:26.4(2) msDecay constant λ:26.25557502121 s^-1Specific activity α:7.187035051652 × 10⁺²² Bq g^-1
1942441905852.1 Ci g^-1Spin and parity:
(nuclear angular momentum)(3-)Year of discovery:1970

Radioactive Decay

Half-life T_½ = 26.4(2) ms respectively 2.64 × 10^-2 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²¹⁶Fr	> 99 %	8.348(4) MeV
EE	²²⁰Ra	5×10^-4 %	3.473(10) MeV

Parent Nuclides

Direct parent isotopes are: ²²⁴Pa, ²²⁰Th.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 131) and isobaric (same nucleon number A = 220) with Actinium-220. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 131	Isobar A = 220
79	²¹⁰Au
80	²¹¹Hg
81	²¹²Tl
82	²¹³Pb	²²⁰Pb
83	²¹⁴Bi	²²⁰Bi
84	²¹⁵Po	²²⁰Po
85	²¹⁶At	²²⁰At
86	²¹⁷Rn	²²⁰Rn
87	²¹⁸Fr	²²⁰Fr
88	²¹⁹Ra	²²⁰Ra
89	²²⁰Ac	²²⁰Ac
90	²²¹Th	²²⁰Th
91	²²²Pa	²²⁰Pa
92	²²³U	²²⁰U