Actinium-228

Properties and data of the isotope ²²⁸Ac.

Contents

Actinium-228 is a radioisotope of the chemical element actinium discovered by Otto Hahn in 1906, which has 139 neutrons in the atomic nucleus in addition to element-specific 89 protons, resulting in the mass number 228 . The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has hardly any practical significance; dealing with ²¹²Ac is for academic purposes only. However, the core properties of the nuclide are well suited for γ-spectroscopy, so that the isotope is currently being researched more closely in this regard and methods for the production of ²²⁸Ac are also being developed [1].

General data

Name of the isotope:Actinium-228; Ac-228Other names:Mesothorium 2. Mesothorium IISymbol:²²⁸Ac or 22889AcMass number A:228 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:139Isotopic mass:228.0310198(22) u (atomic weight of Actinium-228)Nuclide mass:227.9822024 u (calculated nuclear mass without electrons)Mass excess:28.89476 MeVMass defect:1.869831372 u (per nucleus)Nuclear binding energy:1741.73670403 MeV (per nucleus)
7.63919607 MeV (average binding energy per nucleon)Separation energy:S_N = 5.0262(24) MeV (first neutron)
S_P = 5.5719(24) MeV (first proton)Half-life:6.15(2) hDecay constant λ:3.130746072989 × 10^-5 s^-1Specific activity α:8.269207828174 × 10⁺¹⁶ Bq g^-1
2234921.0346418 Ci g^-1Spin and parity:
(nuclear angular momentum)3+Year of discovery:1906

Radioactive Decay

Half-life T_½ = 6.15(2) h (hours) respectively 2.2140 × 10⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	²²⁸Th	100 %	2.1237(26) MeV

The scheme shows the radioactive decay of the isotope actinium-228 and the position of the nuclide in the thorium series, which starts with Th-232 and ends with the stable nuclide Lead-208.

Parent Nuclides

Direct parent isotope is: ²²⁸Ra.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 139) and isobaric (same nucleon number A = 228) with Actinium-228. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 139	Isobar A = 228
83	²²²Bi
84	²²³Po
85	²²⁴At	²²⁸At
86	²²⁵Rn	²²⁸Rn
87	²²⁶Fr	²²⁸Fr
88	²²⁷Ra	²²⁸Ra
89	²²⁸Ac	²²⁸Ac
90	²²⁹Th	²²⁸Th
91	²³⁰Pa	²²⁸Pa
92	²³¹U	²²⁸U
93	²³²Np	²²⁸Np
94	²³³Pu	²²⁸Pu
95	²³⁴Am
96	²³⁵Cm
97	²³⁶Bk
98	²³⁷Cf

External data and identifiers

CAS:4331-83-0InChI Key:QQINRWTZWGJFDB-OUBTZVSYSA-NSMILES:[228Ac]PubChem:ID 105063Adopted Levels, Gammas:NuDat 228Ac

Literature and References

[1] - Kelly E. Aldrich, Mila Nhu Lam, Cecilia Eiroa-Lledo et al.:
Preparation of an Actinium-228 Generator.
In: Inorganic Chemistry, (2020), DOI 10.1021/acs.inorgchem.9b03563.