Actinium-221

Properties and data of the isotope ²²¹Ac.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Actinium-221 is a radioisotope of the chemical element actinium, which, in addition to the element-specific 89 protons, has 132 neutrons in the atomic nucleus, resulting in the mass number 221. The very short-lived, only artificially producible, unstable and therefore radioactive nuclide has no practical significance; dealing with ²²¹Ac is for academic purposes only.

In 1968, a report was published that first described the short-lived isotope actinium-221. In the investigations described therein, protons with energies of 32 to 41.6 MeV collided with an enriched uranium-233 template, resulting in the reaction ²³³U(p,5n)²²⁹Np, which initially produced neptunium-229. The radioactive decay products were subsequently analyzed, and the properties of one of the decay products could be clearly attributed to the previously unknown nuclide actinium-221 [1].

See also: List of individual Actinium isotopes (and general data sources).

General data

Name of the isotope:Actinium-221; Ac-221Symbol:²²¹Ac or 22189AcMass number A:221 (= number of nucleons)Atomic number Z:89 (= number of protons)Neutrons N:132Isotopic mass:221.015600(60) u (atomic weight of Actinium-221)Nuclide mass:220.9667826 u (calculated nuclear mass without electrons)Mass excess:14.53131 MeVMass defect:1.82459676 u (per nucleus)Nuclear binding energy:1699.60093436 MeV (per nucleus)
7.69050197 MeV (average binding energy per nucleon)Separation energy:S_N = 7.284(57) MeV (first neutron)
S_P = 3.030(57) MeV (first proton)Half-life:52(2) msDecay constant λ:13.329753472307 s^-1Specific activity α:3.632291992690 × 10⁺²² Bq g^-1
981700538565.03 Ci g^-1Spin and parity:
(nuclear angular momentum)(5/2-)Year of discovery:1968

Radioactive Decay

Half-life T_½ = 52(2) ms respectively 5.2 × 10^-2 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²¹⁷Fr	100 %	7.791(57) MeV

Parent Nuclides

Direct parent isotope is: ²²⁵Pa.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 132) and isobaric (same nucleon number A = 221) with Actinium-221. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 132	Isobar A = 221
80	²¹²Hg
81	²¹³Tl
82	²¹⁴Pb
83	²¹⁵Bi	²²¹Bi
84	²¹⁶Po	²²¹Po
85	²¹⁷At	²²¹At
86	²¹⁸Rn	²²¹Rn
87	²¹⁹Fr	²²¹Fr
88	²²⁰Ra	²²¹Ra
89	²²¹Ac	²²¹Ac
90	²²²Th	²²¹Th
91	²²³Pa	²²¹Pa
92	²²⁴U	²²¹U
93	²²⁵Np	²²¹Np

Data changes (history)

Nuclear spin: Spin and parity assignments in the ground state of ²²¹Ac were remeasured in 2022 and a value of I^π = 5/2^- was proposed, which has been adopted here [2]. The preliminary values (3/2-) and (9/2-) (NUBASE2020) can be found in the relevant data tables.

External data and identifiers

Adopted Levels, Gammas:NuDat 221Ac

Literature and References

[1] - R. L. Hahn, M. F. Roche, K. S Toth:
New neptunium isotopes, ²³⁰Np and ²²⁹Np.
In: Nuclear Physics A, 113, 1, (1968), DOI 10.1016/0375-9474(68)90894-4.

[2] - E. Parr et al.:
Single-particle states and parity doublets in odd-Z ²²¹Ac and ²²⁵Pa from α-decay spectroscopy.
In: Physical Review C, 105, 034303, (2022), DOI 10.1103/PhysRevC.105.034303.

[3] - E. Rey-herme et al.:
Level structure of ²²¹Ac and ²¹⁷Fr from decay spectroscopy, and reflection asymmetry in ²²¹Ac.
In: Physical Review C, 108, 014304, (2023), DOI 10.1103/PhysRevC.108.014304.