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Radioactive elements

Radioactive elements do not have standard atomic weights but many versions of the Periodic Tables include the mass number of the most stable isotopes, usually in square brackets. Below is the compilation of such isotopes from the most recent authoritative work The 2012 Nubase Evaluation.

Most stable known isotopes of radioactive elements

Z Symbol Element Mass
number
Half-life
43Tctechnetium974.21(16) Ma
984.2(3) Ma
61Pmpromethium14517.7(4) a
84Popolonium209102(5) a
85Atastatine2108.1(4) h
86Rnradon2223.8235(3) d
87Frfrancium22322.00(7) min
88Raradium2261600(7) a
89Acactinium22721.772(3) a
93Npneptunium2372144(7) ka
94Puplutonium24480(0.9) Ma
95Amamericium2437.37(4) ka
96Cmcurium24715.6(5) Ma
97Bkberkelium2471.38(25) ka
98Cfcalifornium251900(40) a
99Eseinsteinium252471.7(1.9) d
100Fmfermium257100.5(0.2) d
101Mdmendelevium25851.5(0.3) d
102Nonobelium25958(5) min
103Lrlawrencium2624(1) h
104Rfrutherfordium2672.5(1.5) h
105Dbdubnium26830.8(5.0) h
27090(70) h
106Sgseaborgium2698(6) min
2713.1(1.6) min
107Bhbohrium2703.8(3.0) min
2743.4(2.7) min
108Hshassium26927(17) s
277130(100) s
109Mtmeitnerium27610(5) s
27829(23) s
110Dsdarmstadtium28114(4) s
111Rgroentgenium 28137(17) s
112Cncopernicium28532(9) s
113Nhnihonium28670(60) s
114Flflerovium2892.4(6) s
115Mcmoscovium288190(40) ms
289340(180) ms
116Lvlivermorium29380(40) ms
117Tstennessine294290(230) ms
118Ogoganesson2941.4(7) ms
Z Symbol Element Mass
number
Half-life

Notes      Back to Top
Uncertainties associated with the quoted half-live values are given as standard uncertainties (1s) applicable to the last digits. For example, a value of 1.4(7) ms refers to 1.4 ms with a standard uncertainty of 0.7 ms whereas a value of 3.1(1.6) min refers to 3.1 min with a standard uncertainty of 1.6 min.
Half-lives are given in standard units of time (a=year, d=day, min=minute, s=second).

Radioactive symbol

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G. Audi et al
The NUBASE2012 Evaluation of Nuclear Properties Chinese Physics C, 2012 (36) 1157-1286

For some elements, there is no single isotope which could be regarded as the most stable (longest lived). This is because the half-lives are measured with asymmetric uncertainties whereas the recommended values have mathematically calculated symmetric uncertainties. Thus, for example, technetium-97 and technetium-98 could both be considered as equaly stable. Likewise, one cannot readily distinguish between the longevity of bohrium-270 (t1/2 = 3.8(3.0) min) and bohrium-274 (t1/2 = 3.4(2.7) min).