Iridium-189

Properties and data of the isotope ¹⁸⁹Ir.

Contents

Iridium-189 is a radioisotope of the chemical element iridium, which has 112 neutrons in its atomic nucleus in addition to the element-specific 77 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 189. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ¹⁸⁹Ir is exclusively for academic purposes.

General data

Name of the isotope:Iridium-189; Ir-189Symbol:¹⁸⁹Ir or 18977IrMass number A:189 (= number of nucleons)Atomic number Z:77 (= number of protons)Neutrons N:112Isotopic mass:188.958723(14) u (atomic weight of Iridium-189)Nuclide mass:188.9164868 u (calculated nuclear mass without electrons)Mass excess:-38.44928 MeVMass defect:1.614275056 u (per nucleus)Nuclear binding energy:1503.68752901 MeV (per nucleus)
7.95601867 MeV (average binding energy per nucleon)Separation energy:S_N = 8.176(16) MeV (first neutron)
S_P = 4.601(13) MeV (first proton)Half-life:13.2(1) dDecay constant λ:6.077679403057 × 10^-7 s^-1Specific activity α:1.946842631210 × 10⁺¹⁵ Bq g^-1
52617.368411086 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2+Magnetic dipole moment:μ(μ_N) = +0.147(7)Quadrupole moment Q:+ 0.828(8) barn (100 fm²)Nuclear g-factor:g_l = 0.098Charge radius:5.3898(1061) femtometer fmYear of discovery:1955

Radioactive Decay

Half-life T_½ = 13.2(1) d respectively 1.140480 × 10⁶ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC	¹⁸⁹Os	100 %	0.537(13) MeV

Parent Nuclides

Direct parent isotope is: ¹⁸⁹Pt.

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
^189m1Ir	372.17(4) keV	13.3(3) ms	11/2-
^189m2Ir	2333.2(5) keV	3.7(2) ms	(25/2)+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 112) and isobaric (same nucleon number A = 189) with Iridium-189. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 112	Isobar A = 189
70	¹⁸²Yb
71	¹⁸³Lu
72	¹⁸⁴Hf	¹⁸⁹Hf
73	¹⁸⁵Ta	¹⁸⁹Ta
74	¹⁸⁶W	¹⁸⁹W
75	¹⁸⁷Re	¹⁸⁹Re
76	¹⁸⁸Os	¹⁸⁹Os
77	¹⁸⁹Ir	¹⁸⁹Ir
78	¹⁹⁰Pt	¹⁸⁹Pt
79	¹⁹¹Au	¹⁸⁹Au
80	¹⁹²Hg	¹⁸⁹Hg
81	¹⁹³Tl	¹⁸⁹Tl
82	¹⁹⁴Pb	¹⁸⁹Pb
83	¹⁹⁵Bi	¹⁸⁹Bi
84	¹⁹⁶Po	¹⁸⁹Po
85	¹⁹⁷At
86	¹⁹⁸Rn
87	¹⁹⁹Fr