Naturally occurring tellurium on Earth consists of eight isotopes: 120, 122-126, 128, 130. The heaviest two have been found to be radioactive: 128Te and 130Te undergo double beta decay with half-lives of, respectively, 7.7×1024 years (the longest half-life of all nuclides proven to be radioactive) and 7.9×1020 years. Artificial radioisotopes of tellurium are known, with atomic masses that range from 104 to 142, of which the most stable is 121Te with a half-life of 19.31 days. Several nuclear isomers have longer half-lives, the longest being 121mTe with a half-life of 164.7 days.

The very long-lived radioisotopes 128Te and 130Te are the two most common isotopes of tellurium. Of elements with at least one stable isotope, only indium and rhenium likewise have a radioisotope in greater abundance than a stable one.

It has been claimed that electron capture of 123Te was observed, but more recent measurements of the same team have disproved this. They have determined the half-life of 123Te to be longer than 9.2 × 1016 years (or 2 × 1015 years without any theoretical assumptions). Its observational stability presents one of only two apparent violations of the Mattauch isobar rule, the other involving 180mTa.

124Te is used as the starting material in the production of certain radionuclides by a cyclotron or other particle accelerator, such as iodine-123 and iodine-124.

With the exception of beryllium, tellurium is the lightest element observed to have isotopes capable of undergoing alpha decay, with isotopes 104Te to 109Te being seen to undergo this mode of decay. Some lighter elements, namely those in the vicinity of 8Be, have isotopes with delayed alpha emission (following proton or beta emission) as a rare branch.

List of isotopes

NuclideZNIsotopic mass (Da)Discovery yearHalf-lifeDecay modeDaughter isotopeSpin and parityNatural abundance (mole fraction)
Excitation energyNormal proportionRange of variation
104Te5252103.94672(34)<4 nsα100Sn0+
105Te5253104.94363(32)#633(66) nsα101Sn(7/2+)
106Te5254105.93750(11)78(11) μsα102Sn0+
107Te5255106.934868(18)3.22(9) msα (70%)103Sn5/2+#
β+ (30%)107Sb
108Te5256107.9293805(58)2.1(1) sα (49%)104Sn0+
β+ (48.6%)108Sb
β+, p (2.4%)107Sn
β+, α (<0.065%)104In
109Te5257108.9273045(47)4.4(2) sβ+ (86.7%)109Sb(5/2+)
β+, p (9.4%)108Sn
α (3.9%)105Sn
β+, α (<0.0049%)105In
110Te5258109.9224581(71)18.6(8) sβ+110Sb0+
111Te5259110.9210006(69)26.2(6) sβ+111Sb(5/2)+
β+, p (?%)110Sn
112Te5260111.9167278(90)2.0(2) minβ+112Sb0+
113Te5261112.915891(30)1.7(2) minβ+113Sb(7/2+)
114Te5262113.912088(26)15.2(7) minβ+114Sb0+
115Te5263114.911902(30)5.8(2) minβ+115Sb7/2+
115m1Te10(6) keV6.7(4) minβ+115Sb(1/2+)
115m2Te280.05(20) keV7.5(2) μsIT115Te11/2−
116Te5264115.908466(26)2.49(4) hβ+116Sb0+
117Te5265116.908646(14)62(2) minEC (75%)117Sb1/2+
β+ (25%)
117mTe296.1(5) keV103(3) msIT117Te(11/2−)
118Te5266117.905860(20)6.00(2) dEC118Sb0+
119Te5267118.9064057(78)16.05(5) hEC (97.94%)119Sb1/2+
β+ (2.06%)
119mTe260.96(5) keV4.70(4) dEC (99.59%)119Sb11/2−
β+ (0.41%)
120Te5268119.9040658(19)Observationally Stable0+9(1)×10−4
121Te5269120.904945(28)19.31(7) dβ+121Sb1/2+
121mTe293.974(22) keV164.7(5) dIT (88.6%)121Te11/2−
β+ (11.4%)121Sb
122Te5270121.9030447(15)Stable0+0.0255(12)
123Te5271122.9042710(15)Observationally Stable1/2+0.0089(3)
123mTe247.47(4) keV119.2(1) dIT123Te11/2−
124Te5272123.9028183(15)Stable0+0.0474(14)
125Te5273124.9044312(15)Stable1/2+0.0707(15)
125mTe144.775(8) keV57.40(15) dIT125Te11/2−
126Te5274125.9033121(15)Stable0+0.1884(25)
127Te5275126.9052270(15)9.35(7) hβ−127I3/2+
127mTe88.23(7) keV106.1(7) dIT (97.86%)127Te11/2−
β− (2.14%)127I
128Te5276127.90446124(76)7.7(4)×1024 yβ−β−128Xe0+0.3174(8)
128mTe2790.8(3) keV363(27) nsIT128Te(10+)
129Te5277128.90659642(76)69.6(3) minβ−129I3/2+
129mTe105.51(3) keV33.6(1) dIT (64%)129Te11/2−
β− (36%)129I
130Te5278129.906222745(11)7.91(21)×1020 yβ−β−130Xe0+0.3408(62)
130m1Te2146.41(4) keV186(11) nsIT130Te7−
130m2Te2667.2(8) keV1.90(8) μsIT130Te(10+)
130m3Te4373.9(9) keV(2014)53(8) nsIT130Te(15−)
131Te5279130.908522210(65)25.0(1) minβ−131I3/2+
131m1Te182.258(18) keV32.48(11) hβ− (74.1%)131I11/2−
IT (25.9%)131Te
131m2Te1940.0(4) keV93(12) msIT131Te(23/2+)
132Te5280131.9085467(37)3.204(13) dβ−132I0+
132m1Te1774.80(9) keV145(8) nsIT132Te6+
132m2Te1925.47(9) keV28.5(9) μsIT132Te7−
132m3Te2723.3(8) keV3.62(6) μsIT132Te(10+)
133Te5281132.9109633(22)12.5(3) minβ−133I3/2+#
133m1Te334.26(4) keV55.4(4) minβ− (83.5%)133I(11/2−)
IT (16.5%)133Te
133m2Te1610.4(5) keV100(5) nsIT133Te(19/2−)
134Te5282133.9113964(29)41.8(8) minβ−134I0+
134mTe1691.34(16) keV164.5(7) nsIT134Te6+
135Te5283134.9165547(18)19.0(2) sβ−135I(7/2−)
135mTe1554.89(16) keV511(20) nsIT135Te(19/2−)
136Te5284135.9201012(24)17.63(9) sβ− (98.63%)136I0+
β−, n (1.37%)135I
137Te5285136.9255994(23)2.49(5) sβ− (97.06%)137I3/2−#
β−, n (2.94%)136I
138Te5286137.9294725(41)1.46(25) sβ− (95.20%)138I0+
β−, n (4.80%)137I
139Te5287138.9353672(38)724(81) msβ−139I5/2−#
140Te5288139.939487(15)351(5) msβ− (?%)140I0+
β−, n (?%)139I
141Te5289140.94560(43)#193(16) msβ−141I5/2−#
142Te5290141.95003(54)#147(8) msβ−142I0+
143Te5291142.95649(54)#120(8) msβ−143I7/2+#
144Te5292143.96112(32)#93(60) msβ−144I0+
145Te5293144.96778(32)#75# ms [>550 ns]β−145I
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See also

Daughter products other than tellurium