Actinium-204

Properties and data of the isotope ²⁰⁴Ac.

Content

Actinium-204 is a radioisotope of the element actinium, whose atomic nucleus has 115 neutrons in addition to the element-specific 89 protons, resulting in a mass number of 204.

The generation of this short-lived isotope was first reported in 2022; it was produced in a fusion-evaporation reaction: ¹⁶⁹Tm(⁴⁰Ca,5n) ²⁰⁴Ac [1].

General data

Name of the isotope:Actinium-204; Ac-204Symbol:²⁰⁴AcMass number A:204Atomic number Z:89 (= number of protons)Neutrons N:115Isotopic mass:204 u (atomic weight of Actinium-204)Nuclide mass:203.9511826 u (calculated nuclear mass without electrons)Mass excess:0 MeVMass defect:1.692893188 u (per nucleus)Nuclear binding energy:1576.91984726 MeV (per nucleus)
7.72999925 MeV (average binding energy per nucleon)Half-life:7.4 msDecay constant λ:93.668537913506 s^-1Spin and parity:Year of discovery:2022

Radioactive Decay

Half-life T_½ = 7.4 ms respectively 7.4 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰⁰Fr	?

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 115) and isobaric (same nucleon number A = 204) with Actinium-204. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 115	Isobar A = 204
70	¹⁸⁵Yb
71	¹⁸⁶Lu
72	¹⁸⁷Hf
73	¹⁸⁸Ta
74	¹⁸⁹W
75	¹⁹⁰Re
76	¹⁹¹Os
77	¹⁹²Ir	²⁰⁴Ir
78	¹⁹³Pt	²⁰⁴Pt
79	¹⁹⁴Au	²⁰⁴Au
80	¹⁹⁵Hg	²⁰⁴Hg
81	¹⁹⁶Tl	²⁰⁴Tl
82	¹⁹⁷Pb	²⁰⁴Pb
83	¹⁹⁸Bi	²⁰⁴Bi
84	¹⁹⁹Po	²⁰⁴Po
85	²⁰⁰At	²⁰⁴At
86	²⁰¹Rn	²⁰⁴Rn
87	²⁰²Fr	²⁰⁴Fr
88	²⁰³Ra	²⁰⁴Ra
89	²⁰⁴Ac	²⁰⁴Ac

External data and identifiers

Adopted Levels, Gammas:NuDat 204Ac

Literature and References

[1] - M. H. Huang, Z. G. Gan, Z. Y. Zhang et al.:
α Decay of the new Isotope ²⁰⁴Ac.
In: Physics Letters B, (2022), DOI 10.1016/j.physletb.2022.137484.