# Isotopes of lanthanum

Naturally occurring lanthanum ($_{57}$La) is composed of one stable ($^{139}$La) and one radioactive ($^{138}$La) isotope, with the stable isotope, $^{139}$La, being the most abundant (99.91% natural abundance). There are 39 radioisotopes that have been characterized, with the most stable being $^{138}$La, with a half-life of 1.03×10$^{11}$ years; $^{137}$La, with a half-life of 60,000 years and $^{140}$La, with a half-life of 1.6781 days. The remaining radioactive isotopes have half-lives that are less than a day and the majority of these have half-lives that are less than 1 minute. This element also has 12 nuclear isomers, the longest-lived of which is $^{132m}$La, with a half-life of 24.3 minutes. Lighter isotopes mostly decay to isotopes of barium and heavy ones mostly decay to isotopes of cerium. $^{138}$La can decay to both.
The isotopes of lanthanum range in atomic weight from 115.96 u ($^{116}$La) to 154.96 u ($^{155}$La).

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{116}$La | 57 | 59 | 115.95701(35)# | 50(22) ms | p (~60%) | $^{115}$Ba | | | |
| $^{116}$La | 57 | 59 | 115.95701(35)# | 50(22) ms | β$^+$ (~40%) | $^{116}$Ba | | | |
| $^{116m}$La | 182 keV | 182 keV | 182 keV | 2.0+2.8 −0.8 μs | IT | $^{116}$La | | | |
| $^{117}$La | 57 | 60 | 116.95033(22)# | 21.6(31) ms | p (94%) | $^{116}$Ba | (3/2+) | | |
| $^{117}$La | 57 | 60 | 116.95033(22)# | 21.6(31) ms | β$^+$ (6%) | $^{117}$Ba | (3/2+) | | |
| $^{117m}$La | 192 keV | 192 keV | 192 keV | 3.9+1.9 −0.9 μs | IT | $^{117}$La | (7/2−) | | |
| $^{120}$La | 57 | 63 | 119.93820(32)# | 2.8(2) s | β$^+$ | $^{120}$Ba | 4+ | | |
| $^{120}$La | 57 | 63 | 119.93820(32)# | 2.8(2) s | β$^+$, p (?%) | $^{119}$Cs | 4+ | | |
| $^{121}$La | 57 | 64 | 120.93324(32)# | 5.3(2) s | β$^+$ | $^{121}$Ba | 11/2−# | | |
| $^{122}$La | 57 | 65 | 121.93071(32)# | 8.6(5) s | β$^+$ | $^{122}$Ba | 2+ | | |
| $^{122}$La | 57 | 65 | 121.93071(32)# | 8.6(5) s | β$^+$, p (?%) | $^{121}$Cs | 2+ | | |
| $^{123}$La | 57 | 66 | 122.92630(21)# | 17(3) s | β$^+$ | $^{123}$Ba | 11/2−# | | |
| $^{124}$La | 57 | 67 | 123.924574(61) | 29.21(17) s | β$^+$ | $^{124}$Ba | (7−, 8−) | | |
| $^{124m}$La | 100(100)# keV | 100(100)# keV | 100(100)# keV | 21(4) s | β$^+$ | $^{124}$Ba | 2−# | | |
| $^{125}$La | 57 | 68 | 124.920816(28) | 64.8(12) s | β$^+$ | $^{125}$Ba | 11/2−# | | |
| $^{125m}$La | 107.00(10) keV | 107.00(10) keV | 107.00(10) keV | 390(40) ms | IT | $^{125}$La | (3/2+) | | |
| $^{126}$La | 57 | 69 | 125.919513(97) | 54(2) s | β$^+$ | $^{126}$Ba | 5−# | | |
| $^{126m}$La | 210(410) keV | 210(410) keV | 210(410) keV | 20(20) s | β$^+$ | $^{126}$Ba | 1−# | | |
| $^{127}$La | 57 | 70 | 126.916375(28) | 5.1(1) min | β$^+$ | $^{127}$Ba | (11/2−) | | |
| $^{127m}$La | 14.2(4) keV | 14.2(4) keV | 14.2(4) keV | 3.7(4) min | β$^+$ | $^{127}$Ba | (3/2+) | | |
| $^{128}$La | 57 | 71 | 127.915592(58) | 5.18(14) min | β$^+$ | $^{128}$Ba | (5+) | | |
| $^{128m}$La | 100(100)# keV | 100(100)# keV | 100(100)# keV | <1.4 min | β$^+$ | $^{128}$Ba | (1+, 2−) | | |
| $^{129}$La | 57 | 72 | 128.912696(23) | 11.6(2) min | β$^+$ | $^{129}$Ba | (3/2+) | | |
| $^{129m}$La | 172.33(20) keV | 172.33(20) keV | 172.33(20) keV | 560(50) ms | IT | $^{129}$La | (11/2−) | | |
| $^{130}$La | 57 | 73 | 129.912369(28) | 8.7(1) min | β$^+$ | $^{130}$Ba | 3(+) | | |
| $^{130m}$La | 214.0(5) keV | 214.0(5) keV | 214.0(5) keV | 742(28) ns | IT | $^{130}$La | (5+) | | |
| $^{131}$La | 57 | 74 | 130.910070(30) | 59(2) min | β$^+$ | $^{131}$Ba | 3/2+ | | |
| $^{131m}$La | 304.52(24) keV | 304.52(24) keV | 304.52(24) keV | 170(10) μs | IT | $^{131}$La | 11/2− | | |
| $^{132}$La | 57 | 75 | 131.910119(39) | 4.59(4) h | β$^+$ | $^{132}$Ba | 2− | | |
| $^{132m}$La | 188.20(11) keV | 188.20(11) keV | 188.20(11) keV | 24.3(5) min | IT (76%) | $^{132}$La | 6− | | |
| $^{132m}$La | 188.20(11) keV | 188.20(11) keV | 188.20(11) keV | 24.3(5) min | β$^+$ (24%) | $^{132}$Ba | 6− | | |
| $^{133}$La | 57 | 76 | 132.908218(30) | 3.912(8) h | β$^+$ | $^{133}$Ba | 5/2+ | | |
| $^{134}$La | 57 | 77 | 133.908514(21) | 6.45(16) min | β$^+$ | $^{134}$Ba | 1+ | | |
| $^{134m}$La | 440(100)# keV | 440(100)# keV | 440(100)# keV | 29(4) μs | IT | $^{134}$La | (6−) | | |
| $^{135}$La | 57 | 78 | 134.906984(10) | 18.91(2) h | β$^+$ | $^{135}$Ba | 5/2+ | | |
| $^{136}$La | 57 | 79 | 135.907635(57) | 9.87(3) min | β$^+$ | $^{136}$Ba | 1+ | | |
| $^{136m1}$La | 259.5(3) keV | 259.5(3) keV | 259.5(3) keV | 114(5) ms | IT | $^{136}$La | (7−) | | |
| $^{136m2}$La | 2520.6(4) keV | 2520.6(4) keV | 2520.6(4) keV | 187(27) ns | IT | $^{136}$La | (14+) | | |
| $^{137}$La | 57 | 80 | 136.9064504(18) | 6(2)×10$^4$ y | EC | $^{137}$Ba | 7/2+ | | |
| $^{137m}$La | 1869.50(21) keV | 1869.50(21) keV | 1869.50(21) keV | 342(25) ns | IT | $^{137}$La | 19/2− | | |
| $^{138}$La | 57 | 81 | 137.90712404(45) | 1.03(1)×10$^{11}$ y | β$^+$ (65.5%) | $^{138}$Ba | 5+ | 8.881(71)×10$^{−4}$ | |
| $^{138}$La | 57 | 81 | 137.90712404(45) | 1.03(1)×10$^{11}$ y | β$^−$ (34.5%) | $^{138}$Ce | 5+ | 8.881(71)×10$^{−4}$ | |
| $^{138m1}$La | 72.57(3) keV | 72.57(3) keV | 72.57(3) keV | 116(5) ns | IT | $^{138}$La | (3)+ | | |
| $^{138m2}$La | 738.80(20) keV | 738.80(20) keV | 738.80(20) keV | 2.0(3) μs | IT | $^{138}$La | 7− | | |
| $^{139}$La | 57 | 82 | 138.90636293(65) | Stable | Stable | Stable | 7/2+ | 0.9991119(71) | |
| $^{139m}$La | 1800.4(4) keV | 1800.4(4) keV | 1800.4(4) keV | 315(35) ns | IT | $^{139}$La | (17/2+) | | |
| $^{140}$La | 57 | 83 | 139.90948729(65) | 40.289(4) h | β$^−$ | $^{140}$Ce | 3− | | |
| $^{141}$La | 57 | 84 | 140.9109712(44) | 3.92(3) h | β$^−$ | $^{141}$Ce | (7/2+) | | |
| $^{142}$La | 57 | 85 | 141.9140908(67) | 91.1(5) min | β$^−$ | $^{142}$Ce | 2− | | |
| $^{142m}$La | 145.82(8) keV | 145.82(8) keV | 145.82(8) keV | 0.87(17) μs | IT | $^{142}$La | (4)− | | |
| $^{143}$La | 57 | 86 | 142.9160795(79) | 14.2(1) min | β$^−$ | $^{143}$Ce | (7/2)+ | | |
| $^{144}$La | 57 | 87 | 143.919646(14) | 44.0(7) s | β$^−$ | $^{144}$Ce | (3−) | | |
| $^{145}$La | 57 | 88 | 144.921808(13) | 24.8(20) s | β$^−$ | $^{145}$Ce | (5/2+) | | |
| $^{146}$La | 57 | 89 | 145.9256880(18) | 9.9(1) s | β$^−$ | $^{146}$Ce | (5−) | | |
| $^{146m}$La | 141.5(24) keV | 141.5(24) keV | 141.5(24) keV | 6.08(22) s | β$^−$ | $^{146}$Ce | (1−, 2−) | | |
| $^{147}$La | 57 | 90 | 146.928418(12) | 4.026(20) s | β$^−$ (99.96%) | $^{147}$Ce | (5/2+) | | |
| $^{147}$La | 57 | 90 | 146.928418(12) | 4.026(20) s | β$^−$, n (0.041%) | $^{146}$Ce | (5/2+) | | |
| $^{148}$La | 57 | 91 | 147.932679(21) | 1.414(25) s | β$^−$ (99.82%) | $^{148}$Ce | (2−) | | |
| $^{148}$La | 57 | 91 | 147.932679(21) | 1.414(25) s | β$^−$, n (0.18%) | $^{147}$Ce | (2−) | | |
| $^{149}$La | 57 | 92 | 148.93535(21) | 1.071(22) s | β$^−$ (98.57%) | $^{149}$Ce | (3/2−) | | |
| $^{149}$La | 57 | 92 | 148.93535(21) | 1.071(22) s | β$^−$, n (1.43%) | $^{148}$Ce | (3/2−) | | |
| $^{150}$La | 57 | 93 | 149.9395475(27) | 504(15) ms | β$^−$ (97.3%) | $^{150}$Ce | (3+) | | |
| $^{150}$La | 57 | 93 | 149.9395475(27) | 504(15) ms | β$^−$, n (2.7%) | $^{149}$Ce | (3+) | | |
| $^{151}$La | 57 | 94 | 150.94277(47) | 465(24) ms | β$^−$ | $^{151}$Ce | 1/2+# | | |
| $^{152}$La | 57 | 95 | 151.94709(32)# | 287(16) ms | β$^−$ | $^{152}$Ce | 2−# | | |
| $^{153}$La | 57 | 96 | 152.95055(32)# | 245(18) ms | β$^−$ | $^{153}$Ce | 1/2+# | | |
| $^{154}$La | 57 | 97 | 153.95542(32)# | 161(15) ms | β$^−$ | $^{154}$Ce | 2−# | | |
| $^{155}$La | 57 | 98 | 154.95928(43)# | 101(28) ms | β$^−$ | $^{155}$Ce | 1/2+# | | |
| $^{156}$La | 57 | 99 | 155.96452(43)# | 84(78) ms | β$^−$ | $^{156}$Ce | 4+# | | |
| $^{157}$La | 57 | 100 | 156.96879(32)# | 30# ms [>550 ns] | | | 1/2+# | | |
| This table header & footer: view ||||||||||
* ↑ $^m$La – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* ↑ Bold half-life – nearly stable, half-life longer than age of universe.
* 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: EC:Electron capture IT:Isomeric transition n:Neutron emission p:Proton emission
* ↑ Bold italics symbol as daughter – Daughter product is nearly stable.
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* 1 2 3 Order of ground state and isomer is uncertain.
* ↑ Primordial radionuclide
* 1 2 Fission product