Isotopes of thallium

The only stable isotopes of thallium (₈₁Tl) are ²⁰³Tl and ²⁰⁵Tl, which make up all natural thallium. The five short-lived isotopes ²⁰⁶Tl through ²¹⁰Tl also occur in nature, but only as part of the natural decay chains of heavier elements. Synthetic radioisotopes are known from ¹⁷⁶Tl to ²¹⁷Tl; the most stable is ²⁰⁴Tl with a half-life of 3.78 years, followed by ²⁰²Tl (half-life 12.31 days) and ²⁰¹Tl (half-life 3.0421 days). The naturally-occurring radioisotopes live minutes only, with the longest being ²⁰⁷Tl, with a half-life of 4.77 minutes. All isotopes of thallium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.

The isotope ²⁰⁴Tl is made by the neutron activation of stable thallium in a nuclear reactor. while ²⁰²Tl can be made in a cyclotron as can ²⁰¹Tl (see section below).

In the fully ionized state, the isotope ²⁰⁵Tl⁸¹⁺ becomes unstable, undergoing bound-state β^− decay to ²⁰⁵Pb⁸¹⁺ with a half-life of days, but ²⁰³Tl remains stable.

²⁰⁵Tl is the decay product of bismuth-209, an isotope that was once thought to be stable but is now known to undergo alpha decay with an extremely long half-life of 2.01×10¹⁹ y. Thus ²⁰⁵Tl is now placed at the end of the neptunium decay chain.

List of isotopes

|-id=Thallium-176 | rowspan=2|¹⁷⁶Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 95 | rowspan=2|176.000628(89) | rowspan=2| | p (50%) | ¹⁷⁵Hg | rowspan=2|(3−,4−) | rowspan=2| | rowspan=2| |- | α (50%) | ¹⁷²Au |-id=Thallium-176m | rowspan=2 style="text-indent:1em" | ^176mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 671&nbsp;keV | rowspan=2| | p (50%) | ¹⁷⁵Hg | rowspan=2| | rowspan=2| | rowspan=2| |- | α (50%) | ^172mAu |-id=Thallium-177 | rowspan=2|¹⁷⁷Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 96 | rowspan=2|176.996414(23) | rowspan=2|18(5)&nbsp;ms | α (73%) | ¹⁷³Au | rowspan=2|(1/2+) | rowspan=2| | rowspan=2| |- | p (27%) | ¹⁷⁶Hg |-id=Thallium-177m | rowspan=2 style="text-indent:1em" | ^177mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 807(18)&nbsp;keV | rowspan=2|230(40)&nbsp;μs | p (51%) | ¹⁷⁶Hg | rowspan=2|(11/2−) | rowspan=2| | rowspan=2| |- | α (49%) | ¹⁷³Au |-id=Thallium-178 | rowspan=3|¹⁷⁸Tl | rowspan=3| | rowspan=3 style="text-align:right" | 81 | rowspan=3 style="text-align:right" | 97 | rowspan=3|177.99505(11)# | rowspan=3|255(9)&nbsp;ms | α (62%) | ¹⁷⁴Au | rowspan=3| (4-,5-) | rowspan=3| | rowspan=3| |- | β⁺ (38%) | ¹⁷⁸Hg |- | β⁺, SF (0.15%) | (various) |-id=Thallium-179 | rowspan=2|¹⁷⁹Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 98 | rowspan=2|178.991122(41) | rowspan=2|437(9)&nbsp;ms | α (60%) | ¹⁷⁵Au | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | β⁺ (40%) | ¹⁷⁹Hg |-id=Thallium-179m1 | style="text-indent:1em" | ^179m1Tl | | colspan="3" style="text-indent:2em" | 825(10)#&nbsp;keV | 1.41(2)&nbsp;ms | α | ¹⁷⁵Au | (11/2−) | | |-id=Thallium-179m2 | style="text-indent:1em" | ^179m2Tl | | colspan="3" style="text-indent:2em" | 904.5(9)&nbsp;keV | 119(14)&nbsp;ns | IT | ¹⁷⁹Tl | (9/2−) | | |-id=Thallium-180 | rowspan=3|¹⁸⁰Tl | rowspan=3| | rowspan=3 style="text-align:right" | 81 | rowspan=3 style="text-align:right" | 99 | rowspan=3|179.989919(75) | rowspan=3|1.09(1)&nbsp;s | β⁺ (93%) | ¹⁸⁰Hg | rowspan=3|(4-) | rowspan=3| | rowspan=3| |- | α (7%) | ¹⁷⁶Au |- | β⁺, SF (0.0032%) | (various) |-id=Thallium-181 | rowspan=2|¹⁸¹Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 100 | rowspan=2|180.9862600(98) | rowspan=2|2.9(1)&nbsp;s | β⁺ (91.4%) | ¹⁸¹Hg | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | α (8.6%) | ¹⁷⁷Au |-id=Thallium-181m | rowspan=2 style="text-indent:1em" | ^181mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 835.9(4)&nbsp;keV | rowspan=2|1.40(3)&nbsp;ms | IT (99.60%) | ¹⁸¹Tl | rowspan=2|(9/2−) | rowspan=2| | rowspan=2| |- | α (0.40%) | ¹⁷⁷Au |-id=Thallium-182 | rowspan=3|¹⁸²Tl | rowspan=3| | rowspan=3 style="text-align:right" | 81 | rowspan=3 style="text-align:right" | 101 | rowspan=3|181.985693(13) | rowspan=3|1.9(1)&nbsp;s | β⁺ (<99.41%) | ¹⁸²Hg | rowspan=3|(4−) | rowspan=3| | rowspan=3| |- | α (>0.49%) | ¹⁷⁸Au |- | β⁺, SF (<3.4%) | ¹⁸²Hg |-id=Thallium-182m | rowspan=2 style="text-indent:1em" | ^182mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 50(50)#&nbsp;keV | rowspan=2|3.1(10)&nbsp;s | β⁺ (97.5%) | ¹⁸²Hg | rowspan=2|(7+) | rowspan=2| | rowspan=2| |- | α (2.5%) | ¹⁷⁸Au |-id=Thallium-183 | rowspan=2|¹⁸³Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 102 | rowspan=2|182.982193(10) | rowspan=2|6.9(7)&nbsp;s | β⁺ (?%) | ¹⁸³Hg | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | α (?%) | ¹⁷⁹Au |-id=Thallium-183m1 | rowspan=3 style="text-indent:1em" | ^183m1Tl | rowspan=3| | rowspan=3 colspan="3" style="text-indent:2em" | 628.7(5)&nbsp;keV | rowspan=3|53.3(3)&nbsp;ms | IT (?%) | ¹⁸³Tl | rowspan=3|(9/2−) | rowspan=3| | rowspan=3| |- | α (1.5%) | ¹⁷⁹Au |- | β⁺ (?%) | ¹⁸³Hg |-id=Thallium-183m2 | style="text-indent:1em" | ^183m2Tl | | colspan="3" style="text-indent:2em" | 975.3(6)&nbsp;keV | 1.48(10)&nbsp;μs | IT | ¹⁸³Tl | (13/2+) | | |-id=Thallium-184 | rowspan=2|¹⁸⁴Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 103 | rowspan=2|183.981875(11) | rowspan=2|9.5(2)&nbsp;s | β⁺ (98.78%) | ¹⁸⁴Hg | rowspan=2|2− | rowspan=2| | rowspan=2| |- | α (1.22%) | ¹⁸⁰Au |-id=Thallium-184m1 | rowspan=2 style="text-indent:1em" | ^184m1Tl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | −50(30)&nbsp;keV | rowspan=2|10.6(5)&nbsp;s | β⁺ (99.53%) | ¹⁸⁴Hg | rowspan=2|(7+) | rowspan=2| | rowspan=2| |- | α (0.47%) | ¹⁸⁰Au |-id=Thallium-184m2 | rowspan=2 style="text-indent:1em" | ^184m2Tl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 450(30)&nbsp;keV | rowspan=2| 47.1(7)&nbsp;ms | IT (99.91%) | | rowspan=2|(10−) | rowspan=2| | rowspan=2| |- | α (0.089%) | ¹⁸⁰Au |-id=Thallium-185 | ¹⁸⁵Tl | | style="text-align:right" | 81 | style="text-align:right" | 104 | 184.978789(22) | 19.5(5)&nbsp;s | β⁺ | ¹⁸⁵Hg | 1/2+ | | |- |-id=Thallium-185m | rowspan=2 style="text-indent:1em" | ^185mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 454.8(15)&nbsp;keV | rowspan=2|1.93(8)&nbsp;s | IT | ¹⁸⁵Tl | rowspan=2|9/2− | rowspan=2| | rowspan=2| |- | α (?%) | ¹⁸¹Au |-id=Thallium-186 | rowspan=2|¹⁸⁶Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 105 | rowspan=2|185.978655(22) | rowspan=2|3.5(5)&nbsp;s | β⁺ (?%) | ¹⁸⁶Hg | rowspan=2|(2−) | rowspan=2| | rowspan=2| |- | α (?%) | ¹⁸²Au |-id=Thallium-186m1 | rowspan=2 style="text-indent:1em" | ^186m1Tl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 20(40)&nbsp;keV | rowspan=2|27.5(10)&nbsp;s | β⁺ (99.99%) | ¹⁸⁶Hg | rowspan=2|7+ | rowspan=2| | rowspan=2| |- | α (0.006%) | ¹⁸²Au |-id=Thallium-186m2 | rowspan=2 style="text-indent:1em" | ^186m2Tl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 390(40)&nbsp;keV | rowspan=2|3.40(9)&nbsp;s | IT (<94.1%) | ¹⁸⁶Tl | rowspan=2|10− | rowspan=2| | rowspan=2| |- | β⁺ (>5.9%) | ¹⁸⁶Hg |-id=Thallium-187 | ¹⁸⁷Tl | | style="text-align:right" | 81 | style="text-align:right" | 106 | 186.9759047(86) | ~51&nbsp;s | β⁺ | ¹⁸⁷Hg | 1/2+ | | |-id=Thallium-187m1 | rowspan=3 style="text-indent:1em" | ^187m1Tl | rowspan=3| | rowspan=3 colspan="3" style="text-indent:2em" | 334(3)&nbsp;keV | rowspan=3|15.60(12)&nbsp;s | β⁺ (?%) | ¹⁸⁷Hg | rowspan=3|9/2− | rowspan=3| | rowspan=3| |- | IT (?%) | ¹⁸⁷Tl |- | α (0.15%) | ¹⁸³Au |-id=Thallium-187m2 | style="text-indent:1em" | ^187m2Tl | | colspan="3" style="text-indent:2em" | 1875(50)#&nbsp;keV | 1.11(7)&nbsp;μs | IT | ¹⁸⁷Tl | | | |-id=Thallium-187m3 | style="text-indent:1em" | ^187m3Tl | | colspan="3" style="text-indent:2em" | 2582.5(3)&nbsp;keV | 693(38)&nbsp;ns | IT | ¹⁸⁷Tl | 29/2+# | | |-id=Thallium-188 | ¹⁸⁸Tl | | style="text-align:right" | 81 | style="text-align:right" | 107 | 187.976021(32) | 71(2)&nbsp;s | β⁺ | ¹⁸⁸Hg | 2−# | | |-id=Thallium-188m1 | style="text-indent:1em" | ^188m1Tl | | colspan="3" style="text-indent:2em" | 30(30)&nbsp;keV | 71.5(15)&nbsp;s | β⁺ | ¹⁸⁸Hg | 7+ | | |-id=Thallium-188m2 | style="text-indent:1em" | ^188m2Tl | | colspan="3" style="text-indent:2em" | 299(30)&nbsp;keV | 41(4)&nbsp;ms | IT | ¹⁸⁸Tl | 9− | | |-id=Thallium-189 | ¹⁸⁹Tl | | style="text-align:right" | 81 | style="text-align:right" | 108 | 188.9735735(90) | 2.3(2)&nbsp;min | β⁺ | ¹⁸⁹Hg | 1/2+ | | |-id=Thallium-189m | style="text-indent:1em" | ^189mTl | | colspan="3" style="text-indent:2em" | 285(6)&nbsp;keV | 1.4(1)&nbsp;min | β⁺ | ¹⁸⁹Hg | 9/2− | | |-id=Thallium-190 | ¹⁹⁰Tl | | style="text-align:right" | 81 | style="text-align:right" | 109 | 189.9738418(78) | 2.6(3)&nbsp;min | β⁺ | ¹⁹⁰Hg | 2− | | |-id=Thallium-190m1 | style="text-indent:1em" | ^190m1Tl | | colspan="3" style="text-indent:2em" | 70(7)&nbsp;keV | 3.6(3)&nbsp;min | β⁺ | ¹⁹⁰Hg | 7+ | | |-id=Thallium-190m2 | style="text-indent:1em" | ^190m2Tl | | colspan="3" style="text-indent:2em" | 306(10)&nbsp;keV | 60#&nbsp;ms | IT | ¹⁹⁰Tl | (9−) | | |-id=Thallium-191 | ¹⁹¹Tl | | style="text-align:right" | 81 | style="text-align:right" | 110 | 190.9717841(79) | 20#&nbsp;min | β⁺ | ¹⁹¹Hg | 1/2+ | | |-id=Thallium-191m | style="text-indent:1em" | ^191mTl | | colspan="3" style="text-indent:2em" | 297(7)&nbsp;keV | 5.22(16)&nbsp;min | β⁺ | ¹⁹¹Hg | 9/2− | | |-id=Thallium-192 | ¹⁹²Tl | | style="text-align:right" | 81 | style="text-align:right" | 111 | 191.972225(34) | 9.6(4)&nbsp;min | β⁺ | ¹⁹²Hg | 2− | | |-id=Thallium-192m1 | style="text-indent:1em" | ^192m1Tl | | colspan="3" style="text-indent:2em" | 196(7)&nbsp;keV | 10.8(2)&nbsp;min | β⁺ | ¹⁹²Hg | 7+ | | |-id=Thallium-192m2 | style="text-indent:1em" | ^192m2Tl | | colspan="3" style="text-indent:2em" | 447(7)&nbsp;keV | 296(5)&nbsp;ns | IT | ¹⁹²Tl | (8−) | | |-id=Thallium-192m3 | style="text-indent:1em" | ^192m3Tl | | colspan="3" style="text-indent:2em" | 180(40)&nbsp;keV | | α | ¹⁸⁸Au | (3+) | | |-id=Thallium-193 | ¹⁹³Tl | | style="text-align:right" | 81 | style="text-align:right" | 112 | 192.9705020(72) | 21.6(8)&nbsp;min | β⁺ | ¹⁹³Hg | 1/2+ | | |-id=Thallium-193m | rowspan=2 style="text-indent:1em" | ^193mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 372(4)&nbsp;keV | rowspan=2|2.11(15)&nbsp;min | IT (~75%) | ¹⁹³Tl | rowspan=2|9/2− | rowspan=2| | rowspan=2| |- | β⁺ (~25%) | ¹⁹³Hg |-id=Thallium-194 | ¹⁹⁴Tl | | style="text-align:right" | 81 | style="text-align:right" | 113 | 193.971081(15) | 33.0(5)&nbsp;min | β⁺ | ¹⁹⁴Hg | 2− | | |-id=Thallium-194m | style="text-indent:1em" | ^194mTl | | colspan="3" style="text-indent:2em" | 260(14)&nbsp;keV | 32.8(2)&nbsp;min | β⁺ | ¹⁹⁴Hg | 7+ | | |-id=Thallium-195 | ¹⁹⁵Tl | | style="text-align:right" | 81 | style="text-align:right" | 114 | 194.969774(12) | 1.16(5)&nbsp;h | β⁺ | ¹⁹⁵Hg | 1/2+ | | |-id=Thallium-195m | style="text-indent:1em" | ^195mTl | | colspan="3" style="text-indent:2em" | 482.63(17)&nbsp;keV | 3.6(4)&nbsp;s | IT | ¹⁹⁵Tl | 9/2− | | |-id=Thallium-196 | ¹⁹⁶Tl | | style="text-align:right" | 81 | style="text-align:right" | 115 | 195.970481(13) | 1.84(3)&nbsp;h | β⁺ | ¹⁹⁶Hg | 2− | | |-id=Thallium-196m | rowspan=2 style="text-indent:1em" | ^196mTl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 394.2(5)&nbsp;keV | rowspan=2|1.41(2)&nbsp;h | β⁺ (96.2%) | ¹⁹⁶Hg | rowspan=2|7+ | rowspan=2| | rowspan=2| |- | IT (3.8%) | ¹⁹⁶Tl |-id=Thallium-197 | ¹⁹⁷Tl | | style="text-align:right" | 81 | style="text-align:right" | 116 | 196.969560(15) | 2.84(4)&nbsp;h | β⁺ | ¹⁹⁷Hg | 1/2+ | | |-id=Thallium-197m | style="text-indent:1em" | ^197mTl | | colspan="3" style="text-indent:2em" | 608.22(8)&nbsp;keV | 540(10)&nbsp;ms | IT | ¹⁹⁷Tl | 9/2− | | |-id=Thallium-198 | ¹⁹⁸Tl | | style="text-align:right" | 81 | style="text-align:right" | 117 | 197.9704467(81) | 5.3(5)&nbsp;h | β⁺ | ¹⁹⁸Hg | 2− | | |-id=Thallium-198m1 | rowspan=2 style="text-indent:1em" | ^198m1Tl | rowspan=2| | rowspan=2 colspan="3" style="text-indent:2em" | 543.6(4)&nbsp;keV | rowspan=2|1.87(3)&nbsp;h | β⁺ (55.9%) | ¹⁹⁸Hg | rowspan=2|7+ | rowspan=2| | rowspan=2| |- | IT (44.1%) | ¹⁹⁸Tl |-id=Thallium-198m2 | style="text-indent:1em" | ^198m2Tl | | colspan="3" style="text-indent:2em" | 686.8(5)&nbsp;keV | 150(40)&nbsp;ns | IT | ¹⁹⁸Tl | (5)+ | | |-id=Thallium-198m3 | style="text-indent:1em" | ^198m3Tl | | colspan="3" style="text-indent:2em" | 742.4(4)&nbsp;keV | 32.1(10)&nbsp;ms | IT | ¹⁹⁸Tl | 10− | | |-id=Thallium-199 | ¹⁹⁹Tl | | style="text-align:right" | 81 | style="text-align:right" | 118 | 198.969877(30) | 7.42(8)&nbsp;h | β⁺ | ¹⁹⁹Hg | 1/2+ | | |-id=Thallium-199m | style="text-indent:1em" | ^199mTl | | colspan="3" style="text-indent:2em" | 748.87(6)&nbsp;keV | 28.4(2)&nbsp;ms | IT | ¹⁹⁹Tl | 9/2− | | |-id=Thallium-200 | ²⁰⁰Tl | | style="text-align:right" | 81 | style="text-align:right" | 119 | 199.9709636(62) | 26.1(1)&nbsp;h | β⁺ | ²⁰⁰Hg | 2− | | |-id=Thallium-200m1 | style="text-indent:1em" | ^200m1Tl | | colspan="3" style="text-indent:2em" | 753.60(24)&nbsp;keV | 34.0(9)&nbsp;ms | IT | ²⁰⁰Tl | 7+ | | |-id=Thallium-200m2 | style="text-indent:1em" | ^200m2Tl | | colspan="3" style="text-indent:2em" | 762.00(24)&nbsp;keV | 397(17)&nbsp;ns | IT | ²⁰⁰Tl | 5+ | | |- | ²⁰¹Tl | | style="text-align:right" | 81 | style="text-align:right" | 120 | 200.970820(15) | 3.0421(8)&nbsp;d | EC | ²⁰¹Hg | 1/2+ | | |-id=Thallium-201m | style="text-indent:1em" | ^201mTl | | colspan="3" style="text-indent:2em" | 919.16(21)&nbsp;keV | 2.01(7)&nbsp;ms | IT | ²⁰¹Tl | 9/2− | | |-id=Thallium-202 | ²⁰²Tl | | style="text-align:right" | 81 | style="text-align:right" | 121 | 201.9721089(20) | 12.31(8)&nbsp;d | EC | ²⁰²Hg | 2− | | |-id=Thallium-202m | style="text-indent:1em" | ^202mTl | | colspan="3" style="text-indent:2em" | 950.19(10)&nbsp;keV | 591(3)&nbsp;μs | IT | ²⁰²Tl | 7+ | | |-id=Thallium-203 | ²⁰³Tl | | style="text-align:right" | 81 | style="text-align:right" | 122 | 202.9723441(13) | colspan=3 align=center|Observationally Stable | 1/2+ | 0.29515(44) | |-id=Thallium-203m1 | style="text-indent:1em" | ^203m1Tl | | colspan="3" style="text-indent:2em" | 1483.7(9)&nbsp;keV | <1&nbsp;μs | IT | ²⁰³Tl | (9/2−) | | |-id=Thallium-203m2 | style="text-indent:1em" | ^203m2Tl | | colspan="3" style="text-indent:2em" | 3565(50)#&nbsp;keV | 7.7(5)&nbsp;μs | IT | ²⁰³Tl | (25/2+) | | |-id=Thallium-204 | rowspan=2|²⁰⁴Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 123 | rowspan=2|203.9738634(12) | rowspan=2|3.783(12)&nbsp;y | β^− (97.08%) | ²⁰⁴Pb | rowspan=2|2− | rowspan=2| | rowspan=2| |- | EC (2.92%) | ²⁰⁴Hg |-id=Thallium-204m1 | style="text-indent:1em" | ^204m1Tl | | colspan="3" style="text-indent:2em" | 1104.1(2)&nbsp;keV | 61.7(10)&nbsp;μs | IT | ²⁰⁴Tl | 7+ | | |-id=Thallium-204m2 | style="text-indent:1em" | ^204m2Tl | | colspan="3" style="text-indent:2em" | 2319.0(3)&nbsp;keV | 2.6(2)&nbsp;μs | IT | ²⁰⁴Tl | 12− | | |-id=Thallium-204m3 | style="text-indent:1em" | ^204m3Tl | | colspan="3" style="text-indent:2em" | 4391.6(5)&nbsp;keV | 420(30)&nbsp;ns | IT | ²⁰⁴Tl | 18+ | | |-id=Thallium-204m4 | style="text-indent:1em" | ^204m4Tl | | colspan="3" style="text-indent:2em" | 6239.4(5)&nbsp;keV | 90(3)&nbsp;ns | IT | ²⁰⁴Tl | 22− | | |-id=Thallium-205 | ²⁰⁵Tl | | style="text-align:right" | 81 | style="text-align:right" | 124 | 204.9744273(13) | colspan=3 align=center|Observationally Stable | 1/2+ | 0.70485(44) | |-id=Thallium-205m1 | style="text-indent:1em" | ^205m1Tl | | colspan="3" style="text-indent:2em" | 3290.61(17)&nbsp;keV | 2.6(2)&nbsp;μs | IT | ²⁰⁵Tl | 25/2+ | | |-id=Thallium-205m2 | style="text-indent:1em" | ^205m2Tl | | colspan="3" style="text-indent:2em" | 4835.6(15)&nbsp;keV | 235(10)&nbsp;ns | IT | ²⁰⁵Tl | (35/2–) | | |-id=Thallium-206 | ²⁰⁶Tl | Radium E" | style="text-align:right" | 81 | style="text-align:right" | 125 | 205.9761101(14) | 4.202(11)&nbsp;min | β^− | ²⁰⁶Pb | 0− | Trace | |-id=Thallium-206m | style="text-indent:1em" | ^206mTl | | colspan="3" style="text-indent:2em" | 2643.10(18)&nbsp;keV | 3.74(3)&nbsp;min | IT | ²⁰⁶Tl | (12)– | | |-id=Thallium-207 | ²⁰⁷Tl | Actinium C" | style="text-align:right" | 81 | style="text-align:right" | 126 | 206.9774186(58) | 4.77(2)&nbsp;min | β^− | ²⁰⁷Pb | 1/2+ | Trace | |-id=Thallium-207m | style="text-indent:1em" | ^207mTl | | colspan="3" style="text-indent:2em" | 1348.18(16)&nbsp;keV | 1.33(11)&nbsp;s | IT | ²⁰⁷Tl | 11/2– | | |-id=Thallium-208 | ²⁰⁸Tl | Thorium C" | style="text-align:right" | 81 | style="text-align:right" | 127 | 207.9820180(20) | 3.053(4)&nbsp;min | β^− | ²⁰⁸Pb | 5+ | Trace | |-id=Thallium-208m | style="text-indent:1em" | ^208mTl | | colspan="3" style="text-indent:2em" | 1807(1)&nbsp;keV | 1.3(1)&nbsp;μs | IT | ²⁰⁸Tl | (0–) | | |-id=Thallium-209 | ²⁰⁹Tl | | style="text-align:right" | 81 | style="text-align:right" | 128 | 208.9853517(66) | 2.162(7)&nbsp;min | β^− | ²⁰⁹Pb | 1/2+ | Trace | |-id=Thallium-209m | style="text-indent:1em" | ^209mTl | | colspan="3" style="text-indent:2em" | 1228.1(20)&nbsp;keV | 146(10)&nbsp;ns | IT | ²⁰⁹Tl | 17/2+ | | |-id=Thallium-210 | rowspan=2|²¹⁰Tl | rowspan=2|Radium C″ | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 129 | rowspan=2|209.990073(12) | rowspan=2|1.30(3)&nbsp;min | β^− (99.99%) | ²¹⁰Pb | rowspan=2|5+# | rowspan=2| Trace | rowspan=2| |- | β^−, n (0.009%) | ²⁰⁹Pb |-id=Thallium-210m | style="text-indent:1em" | ^210mTl | | colspan="3" style="text-indent:2em" | 1200(200)#&nbsp;keV | 1#&nbsp;min<br />[>3&nbsp;μs] | | | (9+,10+) | | |-id=Thallium-211 | rowspan=2|²¹¹Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 130 | rowspan=2|210.993475(45) | rowspan=2|81(16)&nbsp;s | β^− (97.8%) | ²¹¹Pb | rowspan=2|1/2+ | rowspan=2| | rowspan=2| |- | β^−, n (2.2%) | ²¹⁰Pb |-id=Thallium-211m | style="text-indent:1em" | ^211mTl | | colspan="3" style="text-indent:2em" | 1244(100)#&nbsp;keV | 580(80)&nbsp;ns | IT | ²¹¹Tl | 17/2+# | | |-id=Thallium-212 | rowspan=2|²¹²Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 131 | rowspan=2|211.99834(22)# | rowspan=2|31(8)&nbsp;s | β^− (98.2%) | ²¹²Pb | rowspan=2|(5+) | rowspan=2| | rowspan=2| |- | β^−, n (1.8%) | ²¹¹Pb |-id=Thallium-213 | rowspan=2|²¹³Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 132 | rowspan=2|213.001915(29) | rowspan=2|23.8(44)&nbsp;s | β^− (92.4%) | ²¹³Pb | rowspan=2|1/2+# | rowspan=2| | rowspan=2| |- | β^−, n (7.6%) | ²¹²Pb |-id=Thallium-213m1 | style="text-indent:1em" | ^213m1Tl | | colspan="3" style="text-indent:2em" | 680(300)#&nbsp;keV | 4.1(5)&nbsp;μs | IT | ²¹³Tl | | | |-id=Thallium-213m2 | style="text-indent:1em" | ^213m2Tl | | colspan="3" style="text-indent:2em" | 1250(100)#&nbsp;keV | 0.6(3)&nbsp;μs | IT | ²¹³Tl | 17/2+# | | |-id=Thallium-214 | rowspan=2|²¹⁴Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 133 | rowspan=2|214.00694(21)# | rowspan=2|11.0(24)&nbsp;s | β^− (66%) | ²¹⁴Pb | rowspan=2|5+# | rowspan=2| | rowspan=2| |- | β^−, n (34%) | ²¹³Pb |-id=Thallium-215 | rowspan=2|²¹⁵Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 134 | rowspan=2|215.01077(32)# | rowspan=2|9.7(38)&nbsp;s | β^− (95.4%) | ²¹⁵Pb | rowspan=2|1/2+# | rowspan=2| | rowspan=2| |- | β^−, n (4.6%) | ²¹⁴Pb |-id=Thallium-216 | rowspan=2|²¹⁶Tl | rowspan=2| | rowspan=2 style="text-align:right" | 81 | rowspan=2 style="text-align:right" | 135 | rowspan=2|216.01596(32)# | rowspan=2|5.9(33)&nbsp;s | β^− (>88.5%) | ²¹⁶Pb | rowspan=2|5+# | rowspan=2| | rowspan=2| |- | β^−, n (<11.5%) | ²¹⁵Pb |-id=Thallium-217 | ²¹⁷Tl | | style="text-align:right" | 81 | style="text-align:right" | 136 | 217.02003(43)# | 2#&nbsp;s<br />[>300&nbsp;ns] | | | 1/2+# | |

Thallium-201

Thallium-201 (²⁰¹Tl) is a synthetic radioisotope of thallium. It has a half-life of 3.0421 days and decays by electron capture, emitting photons consisting mainly of K X-rays (~70–80&nbsp;keV), and gammas of 135 and 167&nbsp;keV (the latter stronger, emitted in 10% of decays). Thallium-201 is synthesized by the neutron activation of stable thallium in a nuclear reactor, or by the ²⁰³Tl(p, 3n)²⁰¹Pb nuclear reaction in cyclotrons, as ²⁰¹Pb then decays to ²⁰¹Tl. It is a radiopharmaceutical, as it has fair imaging characteristics without excessive patient radiation dose. It was the most popular isotope used for nuclear cardiac stress tests.

This nuclide has largely been replaced by technetium-99m, which has a shorter half-life (6 hours instead of 3 days) and a single high-energy photon peak (140 keV), which is better for imaging than the 3 energy peaks of thallium-201. Thallium-201 is now mostly used for myocardial viability studies. It will redistribute in body tissues, whereas Tc will not; Tl is taken up by the cardiac muscle via Na+/K+ pumps. Delayed imaging will show uptake in damaged but still living myocardial cells, which would appear as a scar with Tc or ⁸²Rb.

See also

Daughter products other than thallium

• Isotopes of lead
• Isotopes of mercury
• Isotopes of gold

References