Actinium-203

Properties and data of the isotope ²⁰³Ac.

Contents

Actinium-203 is a radioisotope of the element actinium, whose atomic nucleus has 114 neutrons in addition to the element-specific 89 protons, resulting in a mass number of 203.

The generation of this short-lived isotope was first reported in 2024; it was produced in a fusion-evaporation reaction: ¹⁶⁹Tm(⁴⁰Ca,6n) ²⁰³Ac [1].

General data

Name of the isotope:Actinium-203; Ac-203Symbol:²⁰³Ac or 20389AcMass number A:203 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:114Isotopic mass:203 u (atomic weight of Actinium-203)Nuclide mass:202.9511826 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:1.684228272 u (per nucleus)Nuclear binding energy:1568.84853 MeV (per nucleus)
7.72831788 MeV (average binding energy per nucleon)Separation energy:
S_P = -1.214(22) MeV MeV (first proton)Half-life:0.056 msDecay constant λ:12.377628224285 s^-1Specific activity α:3.671912348698 × 10⁺²² Bq g^-1
992408742891.38 Ci g^-1Spin and parity:
(nuclear angular momentum)(1/2+)Year of discovery:2023

Radioactive Decay

Half-life T_½ = 0.056 ms respectively 5.6 × 10^-2 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁹⁹Fr		8.217(16) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 114) and isobaric (same nucleon number A = 203) with Actinium-203. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 114	Isobar A = 203
70	¹⁸⁴Yb
71	¹⁸⁵Lu
72	¹⁸⁶Hf
73	¹⁸⁷Ta
74	¹⁸⁸W
75	¹⁸⁹Re
76	¹⁹⁰Os	²⁰³Os
77	¹⁹¹Ir	²⁰³Ir
78	¹⁹²Pt	²⁰³Pt
79	¹⁹³Au	²⁰³Au
80	¹⁹⁴Hg	²⁰³Hg
81	¹⁹⁵Tl	²⁰³Tl
82	¹⁹⁶Pb	²⁰³Pb
83	¹⁹⁷Bi	²⁰³Bi
84	¹⁹⁸Po	²⁰³Po
85	¹⁹⁹At	²⁰³At
86	²⁰⁰Rn	²⁰³Rn
87	²⁰¹Fr	²⁰³Fr
88	²⁰²Ra	²⁰³Ra
89	²⁰³Ac	²⁰³Ac

External data and identifiers

Adopted Levels, Gammas:NuDat 203Ac

Literature and References

[1] - J. G. Wang, Z. G. Gan, Z. Y. Zhang et al.:
α-decay properties of new neutron-deficient isotope ²⁰³Ac.
In: Physics Letters B, 850, 138503, (2024), DOI 10.1016/j.physletb.2024.138503.