Actinium-218

Properties and data of the isotope ²¹⁸Ac.

Content

Actinium-218 is a radioisotope of the chemical element actinium, which, in addition to the element-specific 89 protons, has 129 neutrons in the atomic nucleus, resulting in the mass number 218. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ²¹⁸Ac is for academic purposes only.

General data

Name of the isotope:Actinium-218; Ac-218Symbol:²¹⁸Ac or 21889AcMass number A:218 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:129Isotopic mass:218.01164(5) u (atomic weight of Actinium-218)Nuclide mass:217.9628226 u (calculated nuclear mass without electrons)Mass excess:10.84259 MeVMass defect:1.802562012 u (per nucleus)Nuclear binding energy:1679.07569881 MeV (per nucleus)
7.7021821 MeV (average binding energy per nucleon)Separation energy:S_N = 5.93(5) MeV (first neutron)
S_P = 2.34(5) MeV (first proton)Half-life:1.08(9) μsDecay constant λ:641802.94496291 s^-1Specific activity α:1.772948504077 × 10⁺²⁷ Bq g^-1
4.79175271372 × 10⁺¹⁶ Ci g^-1Spin and parity:
(nuclear angular momentum)(1-)Year of discovery:1970

Radioactive Decay

Half-life T_½ = 1.08(9) μs respectively 1.08 × 10^-6 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²¹⁴Fr	100 %	9.38(5) MeV

Parent Nuclides

Direct parent isotope is: ²²²Pa.

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
^218mAc	384.49(13)+y	103(11) ns	(11+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 129) and isobaric (same nucleon number A = 218) with Actinium-218. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 129	Isobar A = 218
78	²⁰⁷Pt
79	²⁰⁸Au
80	²⁰⁹Hg
81	²¹⁰Tl
82	²¹¹Pb	²¹⁸Pb
83	²¹²Bi	²¹⁸Bi
84	²¹³Po	²¹⁸Po
85	²¹⁴At	²¹⁸At
86	²¹⁵Rn	²¹⁸Rn
87	²¹⁶Fr	²¹⁸Fr
88	²¹⁷Ra	²¹⁸Ra
89	²¹⁸Ac	²¹⁸Ac
90	²¹⁹Th	²¹⁸Th
91	²²⁰Pa	²¹⁸Pa
92	²²¹U	²¹⁸U