Thallium (81Tl) has 41 isotopes with atomic masses that range from 176 to 216. 203Tl and 205Tl are the only stable isotopes and 204Tl is the most stable radioisotope with a half-life of 3.78 years. 207Tl, with a half-life of 4.77 minutes, has the longest half-life of naturally occurring Tl radioisotopes. 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.
Thallium-202 (half-life 12.23 days) can be made in a cyclotron[1] while thallium-204 (half-life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.[2]
In the fully ionized state, the isotope 205Tl becomes beta-radioactive, decaying to 205Pb,[3] 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.[4] 205Tl is at the end of the neptunium series decay chain.
|-| rowspan=2|176Tl[5] | rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 95| rowspan=2|176.00059(21)#| rowspan=2|| p (~63%)| 175Hg| rowspan=2|(3-, 4-, 5-)| rowspan=2|| rowspan=2||-| α (~37%)| 172Au|-| rowspan=2 style="text-indent:1em" | 176mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | ~671 keV| rowspan=2|| p (~50%)| 175Hg| rowspan=2|| rowspan=2|| rowspan=2||-| α (~50%)| 172mAu|-| rowspan=2|177Tl[6] | rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 96| rowspan=2|176.996427(27)| rowspan=2|18(5) ms| α (73%)| 173Au| rowspan=2|(1/2+)| rowspan=2|| rowspan=2||-| p (27%)| 176Hg|-| rowspan=2 style="text-indent:1em" | 177mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 807(18) keV| rowspan=2|230(40) μs| p (51%)| 176Hg| rowspan=2|(11/2−)| rowspan=2|| rowspan=2||-| α (49%)| 173Au|-| rowspan=3|178Tl[7] | rowspan=3|| rowspan=3 style="text-align:right" | 81| rowspan=3 style="text-align:right" | 97| rowspan=3|177.99490(12)#| rowspan=3|255(9) ms| α (62%)| 174Au| rowspan=3| (4-,5-)| rowspan=3|| rowspan=3||-| β+ (38%)| 178Hg|-| β+, SF (0.15%)| (various)|-| rowspan=2|179Tl[8] | rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 98| rowspan=2|178.99109(5)| rowspan=2|437(9) ms| α (60%)| 175Au| rowspan=2|(1/2+)| rowspan=2|| rowspan=2||-| β+ (40%)| 179Hg|-| rowspan=3 style="text-indent:1em" | 179m1Tl| rowspan=3|| rowspan=3 colspan="3" style="text-indent:2em" | 825(10)# keV| rowspan=3|1.41(2) ms| α| 175Au| rowspan=3|(11/2−)| rowspan=3|| rowspan=3||-| IT (rare)| 179Tl|-| β+ (rare)| 179Hg|-| style="text-indent:1em" | 179m2Tl| | colspan="3" style="text-indent:2em" | 904.5(9) keV| 119(14) ns| IT| 179Tl| (9/2−)| | |-| rowspan=3|180Tl[9] | rowspan=3|| rowspan=3 style="text-align:right" | 81| rowspan=3 style="text-align:right" | 99| rowspan=3|179.98991(13)#| rowspan=3|1.09(1) s| β+ (93%)| 180Hg| rowspan=3| 4-#| rowspan=3|| rowspan=3||-| α (7%)| 176Au|-| β+, SF (0.0032%)| 100Ru, 80Kr[10] |-| rowspan=2|181Tl[11] | rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 100| rowspan=2|180.986257(10)| rowspan=2|2.9(1) s| β+ (91.4%)| 181Hg| rowspan=2|1/2+#| rowspan=2|| rowspan=2||-| α (8.6%)| 177Au|-| rowspan=2 style="text-indent:1em" | 181mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 834.9(4) keV| rowspan=2|1.40(3) ms| IT (99.60%)| 181Tl| rowspan=2|(9/2−)| rowspan=2|| rowspan=2||-| α (0.40%)| 177Au|-| rowspan=2|182Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 101| rowspan=2|181.98567(8)| rowspan=2|2.0(3) s| β+ (96%)| 182Hg| rowspan=2|2−#| rowspan=2|| rowspan=2||-| α (4%)| 178Au|-| rowspan=2 style="text-indent:1em" | 182m1Tl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 100(100)# keV| rowspan=2|2.9(5) s| α| 178Au| rowspan=2|(7+)| rowspan=2|| rowspan=2||-| β+ (rare)| 182Hg|-| style="text-indent:1em" | 182m2Tl|| colspan="3" style="text-indent:2em" | 600(140)# keV|||| 10−|||-| 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) s| β+ (98%)| 183Hg| rowspan=2|1/2+#| rowspan=2|| rowspan=2||-| α (2%)| 179Au|-| rowspan=2 style="text-indent:1em" | 183m1Tl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 630(17) keV| rowspan=2|53.3(3) ms| IT (99.99%)| 183Tl| rowspan=2|9/2−#| rowspan=2|| rowspan=2||-| α (.01%)| 179Au|-| style="text-indent:1em" | 183m2Tl|| colspan="3" style="text-indent:2em" | 976.8(3) keV| 1.48(10) μs||| (13/2+)|||-| 184Tl|| style="text-align:right" | 81| style="text-align:right" | 103| 183.98187(5)| 9.7(6) s| β+| 184Hg| 2−#|||-| rowspan=2 style="text-indent:1em" | 184m1Tl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 100(100)# keV| rowspan=2|10# s| β+ (97.9%)| 184Hg| rowspan=2|7+#| rowspan=2|| rowspan=2||-| α (2.1%)| 180Au|-| rowspan=2 style="text-indent:1em" | 184m2Tl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 500(140)# keV| rowspan=2| 47.1 ms| IT (99.911%)|| rowspan=2|(10−)| rowspan=2|| rowspan=2||-| α (.089%)| 180Au|-| rowspan=2|185Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 104| rowspan=2|184.97879(6)| rowspan=2|19.5(5) s| α| 181Au| rowspan=2|1/2+#| rowspan=2|| rowspan=2||-| β+| 185Hg|-| rowspan=3 style="text-indent:1em" | 185mTl| rowspan=3|| rowspan=3 colspan="3" style="text-indent:2em" | 452.8(20) keV| rowspan=3|1.93(8) s| IT (99.99%)| 185Tl| rowspan=3|9/2−#| rowspan=3|| rowspan=3||-| α (.01%)| 181Au|-| β+| 185Hg|-| rowspan=2|186Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 105| rowspan=2|185.97833(20)| rowspan=2|40# s| β+| 186Hg| rowspan=2|(2−)| rowspan=2|| rowspan=2||-| α (.006%)| 182Au|-| style="text-indent:1em" | 186m1Tl|| colspan="3" style="text-indent:2em" | 320(180) keV| 27.5(10) s| β+| 186Hg| (7+)|||-| style="text-indent:1em" | 186m2Tl|| colspan="3" style="text-indent:2em" | 690(180) keV| 2.9(2) s||| (10−)|||-| rowspan=2|187Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 106| rowspan=2|186.975906(9)| rowspan=2|~51 s| β+| 187Hg| rowspan=2|(1/2+)| rowspan=2|| rowspan=2||-| α (rare)| 183Au|-| rowspan=3 style="text-indent:1em" | 187mTl| rowspan=3|| rowspan=3 colspan="3" style="text-indent:2em" | 335(3) keV| rowspan=3|15.60(12) s| α| 183Au| rowspan=3|(9/2−)| rowspan=3|| rowspan=3||-| IT| 187Tl|-| β+| 187Hg|-| 188Tl|| style="text-align:right" | 81| style="text-align:right" | 107| 187.97601(4)| 71(2) s| β+| 188Hg| (2−)|||-| style="text-indent:1em" | 188m1Tl|| colspan="3" style="text-indent:2em" | 40(30) keV| 71(1) s| β+| 188Hg| (7+)|||-| style="text-indent:1em" | 188m2Tl|| colspan="3" style="text-indent:2em" | 310(30) keV| 41(4) ms||| (9−)|||-| 189Tl|| style="text-align:right" | 81| style="text-align:right" | 108| 188.973588(12)| 2.3(2) min| β+| 189Hg| (1/2+)|||-| rowspan=2 style="text-indent:1em" | 189mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 257.6(13) keV| rowspan=2|1.4(1) min| β+ (96%)| 189Hg| rowspan=2|(9/2−)| rowspan=2|| rowspan=2||-| IT (4%)| 189Tl|-| 190Tl|| style="text-align:right" | 81| style="text-align:right" | 109| 189.97388(5)| 2.6(3) min| β+| 190Hg| 2(−)|||-| style="text-indent:1em" | 190m1Tl|| colspan="3" style="text-indent:2em" | 130(90)# keV| 3.7(3) min| β+| 190Hg| 7(+#)|||-| style="text-indent:1em" | 190m2Tl|| colspan="3" style="text-indent:2em" | 290(70)# keV| 750(40) μs||| (8−)|||-| style="text-indent:1em" | 190m3Tl|| colspan="3" style="text-indent:2em" | 410(70)# keV| >1 μs||| 9−|||-| 191Tl|| style="text-align:right" | 81| style="text-align:right" | 110| 190.971786(8)| 20# min| β+| 191Hg| (1/2+)|||-| style="text-indent:1em" | 191mTl|| colspan="3" style="text-indent:2em" | 297(7) keV| 5.22(16) min| β+| 191Hg| 9/2(−)|||-| 192Tl|| style="text-align:right" | 81| style="text-align:right" | 111| 191.97223(3)| 9.6(4) min| β+| 192Hg| (2−)|||-| style="text-indent:1em" | 192m1Tl|| colspan="3" style="text-indent:2em" | 160(50) keV| 10.8(2) min| β+| 192Hg| (7+)|||-| style="text-indent:1em" | 192m2Tl|| colspan="3" style="text-indent:2em" | 407(54) keV| 296(5) ns||| (8−)|||-| 193Tl|| style="text-align:right" | 81| style="text-align:right" | 112| 192.97067(12)| 21.6(8) min| β+| 193Hg| 1/2(+#)|||-| rowspan=2 style="text-indent:1em" | 193mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 369(4) keV| rowspan=2|2.11(15) min| IT (75%)| 193Tl| rowspan=2|9/2−| rowspan=2|| rowspan=2||-| β+ (25%)| 193Hg|-| rowspan=2|194Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 113| rowspan=2|193.97120(15)| rowspan=2|33.0(5) min| β+| 194Hg| rowspan=2|2−| rowspan=2|| rowspan=2||-| α (10−7%)| 190Au|-| style="text-indent:1em" | 194mTl|| colspan="3" style="text-indent:2em" | 300(200)# keV| 32.8(2) min| β+| 194Hg| (7+)|||-| 195Tl|| style="text-align:right" | 81| style="text-align:right" | 114| 194.969774(15)| 1.16(5) h| β+| 195Hg| 1/2+|||-| style="text-indent:1em" | 195mTl|| colspan="3" style="text-indent:2em" | 482.63(17) keV| 3.6(4) s| IT| 195Tl| 9/2−|||-| 196Tl|| style="text-align:right" | 81| style="text-align:right" | 115| 195.970481(13)| 1.84(3) h| β+| 196Hg| 2−|||-| rowspan=2 style="text-indent:1em" | 196mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 394.2(5) keV| rowspan=2|1.41(2) h| β+ (95.5%)| 196Hg| rowspan=2|(7+)| rowspan=2|| rowspan=2||-| IT (4.5%)| 196Tl|-| 197Tl|| style="text-align:right" | 81| style="text-align:right" | 116| 196.969575(18)| 2.84(4) h| β+| 197Hg| 1/2+|||-| style="text-indent:1em" | 197mTl|| colspan="3" style="text-indent:2em" | 608.22(8) keV| 540(10) ms| IT| 197Tl| 9/2−|||-| 198Tl|| style="text-align:right" | 81| style="text-align:right" | 117| 197.97048(9)| 5.3(5) h| β+| 198Hg| 2−|||-| rowspan=2 style="text-indent:1em" | 198m1Tl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 543.5(4) keV| rowspan=2|1.87(3) h| β+ (54%)| 198Hg| rowspan=2|7+| rowspan=2|| rowspan=2||-| IT (46%)| 198Tl|-| style="text-indent:1em" | 198m2Tl|| colspan="3" style="text-indent:2em" | 687.2(5) keV| 150(40) ns||| (5+)|||-| style="text-indent:1em" | 198m3Tl|| colspan="3" style="text-indent:2em" | 742.3(4) keV| 32.1(10) ms||| (10−)#|||-| 199Tl|| style="text-align:right" | 81| style="text-align:right" | 118| 198.96988(3)| 7.42(8) h| β+| 199Hg| 1/2+|||-| style="text-indent:1em" | 199mTl|| colspan="3" style="text-indent:2em" | 749.7(3) keV| 28.4(2) ms| IT| 199Tl| 9/2−|||-| 200Tl|| style="text-align:right" | 81| style="text-align:right" | 119| 199.970963(6)| 26.1(1) h| β+| 200Hg| 2−|||-| style="text-indent:1em" | 200m1Tl|| colspan="3" style="text-indent:2em" | 753.6(2) keV| 34.3(10) ms| IT| 200Tl| 7+|||-| style="text-indent:1em" | 200m2Tl|| colspan="3" style="text-indent:2em" | 762.0(2) keV| 0.33(5) μs||| 5+|||-| 201Tl[12] || style="text-align:right" | 81| style="text-align:right" | 120| 200.970819(16)| 72.912(17) h| EC| 201Hg| 1/2+|||-| style="text-indent:1em" | 201mTl|| colspan="3" style="text-indent:2em" | 919.50(9) keV| 2.035(7) ms| IT| 201Tl| (9/2−)|||-| 202Tl|| style="text-align:right" | 81| style="text-align:right" | 121| 201.972106(16)| 12.23(2) d| β+| 202Hg| 2−|||-| style="text-indent:1em" | 202mTl|| colspan="3" style="text-indent:2em" | 950.19(10) keV| 572(7) μs||| 7+|||-| 203Tl|| style="text-align:right" | 81| style="text-align:right" | 122| 202.9723442(14)| colspan=3 align=center|Observationally Stable[13] | 1/2+| 0.2952(1)| 0.29494–0.29528|-| style="text-indent:1em" | 203mTl|| colspan="3" style="text-indent:2em" | 3400(300) keV| 7.7(5) μs||| (25/2+)|||-| rowspan=2|204Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 123| rowspan=2|203.9738635(13)| rowspan=2|3.78(2) y| β− (97.1%)| 204Pb| rowspan=2|2−| rowspan=2|| rowspan=2||-| EC (2.9%)| 204Hg|-| style="text-indent:1em" | 204m1Tl|| colspan="3" style="text-indent:2em" | 1104.0(4) keV| 63(2) μs||| (7)+|||-| style="text-indent:1em" | 204m2Tl|| colspan="3" style="text-indent:2em" | 2500(500) keV| 2.6(2) μs||| (12−)|||-| style="text-indent:1em" | 204m3Tl|| colspan="3" style="text-indent:2em" | 3500(500) keV| 1.6(2) μs||| (20+)|||-| 205Tl[14] || style="text-align:right" | 81| style="text-align:right" | 124| 204.9744275(14)| colspan=3 align=center|Observationally Stable[15] | 1/2+| 0.7048(1)| 0.70472–0.70506|-| style="text-indent:1em" | 205m1Tl|| colspan="3" style="text-indent:2em" | 3290.63(17) keV| 2.6(2) μs||| 25/2+|||-| style="text-indent:1em" | 205m2Tl|| colspan="3" style="text-indent:2em" | 4835.6(15) keV| 235(10) ns||| (35/2–)|||-| 206Tl| Radium E| style="text-align:right" | 81| style="text-align:right" | 125| 205.9761103(15)| 4.200(17) min| β−| 206Pb| 0−| Trace[16] ||-| style="text-indent:1em" | 206mTl|| colspan="3" style="text-indent:2em" | 2643.11(19) keV| 3.74(3) min| IT| 206Tl| (12–)|||-| 207Tl| Actinium C| style="text-align:right" | 81| style="text-align:right" | 126| 206.977419(6)| 4.77(2) min| β−| 207Pb| 1/2+| Trace[17] ||-| rowspan=2 style="text-indent:1em" | 207mTl| rowspan=2|| rowspan=2 colspan="3" style="text-indent:2em" | 1348.1(3) keV| rowspan=2|1.33(11) s| IT (99.9%)| 207Tl| rowspan=2|11/2–| rowspan=2|| rowspan=2||-| β− (.1%)| 207Pb|-| 208Tl| Thorium C"| style="text-align:right" | 81| style="text-align:right" | 127| 207.9820187(21)| 3.053(4) min| β−| 208Pb| 5+| Trace[18] ||-| 209Tl|| style="text-align:right" | 81| style="text-align:right" | 128| 208.985359(8)| 2.161(7) min| β−| 209Pb| 1/2+| Trace[19] ||-| rowspan=2|210Tl| rowspan=2|Radium C″| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 129| rowspan=2|209.990074(12)| rowspan=2|1.30(3) min| β− (99.991%)| 210Pb| rowspan=2|(5+)#| rowspan=2| Trace| rowspan=2||-| β−, n (.009%)| 209Pb|-| rowspan=2|211Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 130| rowspan=2|210.993480(50)| rowspan=2|80(16) s| β− (97.8%)| 211Pb| rowspan=2|1/2+| rowspan=2|| rowspan=2||-| β−, n (2.2%)| 210Pb|-| rowspan=2|212Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 131| rowspan=2|211.998340(220)#| rowspan=2|31(8) s| β− (98.2%)| 212Pb| rowspan=2|(5+)| rowspan=2|| rowspan=2||-| β−, n (1.8%)| 211Pb|-| 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|24(4) s| β− (92.4%)| 213Pb| rowspan=2|1/2+| rowspan=2|| rowspan=2||-| β−, n (7.6%)| 212Pb|-| rowspan=2|214Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 133| rowspan=2|214.006940(210)#| rowspan=2|11(2) s| β− (66%)| 214Pb| rowspan=2|5+#| rowspan=2|| rowspan=2||-| β−, n (34%)| 213Pb|-| rowspan=2|215Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 134| rowspan=2|215.010640(320)#| rowspan=2|10(4) s| β− (95.4%)| 215Pb| rowspan=2|1/2+#| rowspan=2|| rowspan=2||-| β−, n (4.6%)| 214Pb|-| rowspan=2|216Tl| rowspan=2|| rowspan=2 style="text-align:right" | 81| rowspan=2 style="text-align:right" | 135| rowspan=2|216.015800(320)#| rowspan=2|6(3) s| β−| 216Pb| rowspan=2|5+#| rowspan=2|| rowspan=2||-| β−, n (<11.5%)| 215Pb
Thallium-201 (201Tl) is a synthetic radioisotope of thallium. It has a half-life of 73 hours and decays by electron capture, emitting X-rays (~70–80 keV), and photons of 135 and 167 keV in 10% total abundance. Thallium-201 is synthesized by the neutron activation of stable thallium in a nuclear reactor,[20] or by the 203Tl(p, 3n)201Pb nuclear reaction in cyclotrons, as 201Pb naturally decays to 201Tl afterwards.[21] It is a radiopharmaceutical, as it has good imaging characteristics without excessive patient radiation dose. It is the most popular isotope used for thallium nuclear cardiac stress tests.[22]