Isotopes of thallium

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 while thallium-204 (half-life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.

In the fully ionized state, the isotope 205Tl becomes beta-radioactive, decaying to 205Pb, 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. 205Tl is at the end of the neptunium series decay chain.



List of isotopes

 * rowspan=2|176Tl
 * rowspan=2|
 * rowspan=2 style="text-align:right" | 81
 * rowspan=2 style="text-align:right" | 95
 * rowspan=2|176.00059(21)#
 * rowspan=2|$2.4 ms$
 * p (~63%)
 * 175Hg
 * rowspan=2|(3&minus;, 4&minus;, 5&minus;)
 * 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|$290 μs$
 * p (~50%)
 * 175Hg
 * rowspan=2|
 * rowspan=2|
 * rowspan=2|
 * α (~50%)
 * 172mAu
 * rowspan=2|177Tl
 * 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
 * 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
 * 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
 * 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
 * rowspan=2|181Tl
 * 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
 * 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
 * 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
 * style="text-align:right" | 81
 * style="text-align:right" | 124
 * 204.9744275(14)
 * colspan=3 align=center|Observationally Stable
 * 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
 * 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
 * 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
 * 209Tl
 * style="text-align:right" | 81
 * style="text-align:right" | 128
 * 208.985359(8)
 * 2.161(7) min
 * β−
 * 209Pb
 * 1/2+
 * Trace
 * 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
 * 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
 * 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
 * style="text-align:right" | 81
 * style="text-align:right" | 124
 * 204.9744275(14)
 * colspan=3 align=center|Observationally Stable
 * 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
 * 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
 * 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
 * 209Tl
 * style="text-align:right" | 81
 * style="text-align:right" | 128
 * 208.985359(8)
 * 2.161(7) min
 * β−
 * 209Pb
 * 1/2+
 * Trace
 * 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
 * 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
 * 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
 * 215Pb

Thallium-201
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, or by the 203Tl(p, 3n)201Pb nuclear reaction in cyclotrons, as 201Pb naturally decays to 201Tl afterwards. 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.