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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 2016 Nubase Evaluation.

Most stable known isotopes of radioactive elements

Z Symbol Element Mass
43Tctechnetium974.21(16) Ma
984.2(3) Ma
61Pmpromethium14517.7(4) a
84Popolonium209124(3) a
85Atastatine2108.1(4) h
86Rnradon2223.8215(2) d
87Frfrancium22322.00(7) min
88Raradium2261600(7) a
89Acactinium22721.772(3) a
93Npneptunium2372144(7) ka
94Puplutonium24480(0.9) Ma
95Amamericium2437.364(22) 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
105Dbdubnium26829(4) h
2702.0(1.3) h
106Sgseaborgium2695(3) min
2713.1(1.6) min
107Bhbohrium2703.8(3.0) min
27110(8) min
27460(30) s
108Hshassium26916(6) s
2709(4) s
277110(70) s
109Mtmeitnerium27610(5) s
2779(6) s
2787(3) s
110Dsdarmstadtium28011(6) s
28114(4) s
111Rgroentgenium28124(8) s
2821.6(7) min
112Cncopernicium28532(9) s
113Nhnihonium2867(3) s
114Flflerovium2892.4(6) s
115Mcmoscovium288170(25) ms
289310(90) ms
290410(190) ms
116Lvlivermorium29380(40) ms
117Tstennessine29470(30) ms
118Ogoganesson2941.15(47) ms
Z Symbol Element Mass

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


G. Audi et al
The NUBASE2016 Evaluation of Nuclear Properties Chinese Physics C, 2017 (41) 030001

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 equally stable. Likewise, one cannot readily distinguish between the longevity of meitnerium-277 (t1/2 = 9(6) s) and meitnerium-278 (t1/2 = 7(3) s).

Last updated: 29 Aug 2018