Naturally occurring lanthanum (57La) is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.911% natural abundance). There are 39 radioisotopes that have been characterized, with the most stable being 138La, with a half-life of 1.03×1011 years; 137La, with a half-life of 60,000 years and 140La, with a half-life of 40.289 hours. The remaining radioactive isotopes have half-lives that are less than a day and the majority of these less than a minute. This element also has 12 nuclear isomers, the longest-lived of which is 132mLa, 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. 138La can decay to both.
The known isotopes of lanthanum range from 116La to 158La.
List of isotopes
|-id=Lanthanum-116 | rowspan=2|116La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 59 | rowspan=2|115.95701(35)# | rowspan=2 style="text-align:center" | 2022 | rowspan=2|50(22) ms | p (~60%) | 115Ba | rowspan=2| | rowspan=2| | rowspan=2| |- | β+ (~40%) | 116Ba |-id=Lanthanum-116m | style="text-indent:1em" | 116mLa | colspan="3" style="text-indent:2em" | 182 keV | style="text-align:center" |2022 | | IT | 116La
|-id=Lanthanum-117 | rowspan=2|117La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 60 | rowspan=2|116.95033(22)# | rowspan=2 style="text-align:center" | 2001 | rowspan=2|21.6(31) ms | p (94%) | 116Ba | rowspan=2|(3/2+) | rowspan=2| | rowspan=2| |- | β+ (6%) | 117Ba |-id=Lanthanum-117m | style="text-indent:1em" | 117mLa | colspan="3" style="text-indent:2em" | 192 keV | style="text-align:center" | 2022 | | IT | 117La | (7/2−)
|-id=Lanthanum-118 | 118La | style="text-align:right" | 57 | style="text-align:right" | 61 | 117.94673(32)# | style="text-align:center" | 2025 | 200# ms [>310 ns]
| 1−#
|-id=Lanthanum-119 | 119La | style="text-align:right" | 57 | style="text-align:right" | 62 | 118.94093(32)# | style="text-align:center" | 2025 | 1# s [>310 ns]
| 11/2−#
|-id=Lanthanum-120 | rowspan=2|120La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 63 | rowspan=2|119.93820(32)# | rowspan=2 style="text-align:center" | 1984 | rowspan=2|2.8(2) s | β+ | 120Ba | rowspan=2|4+ | rowspan=2| | rowspan=2| |- | β+, p (?%) | 119Cs |-id=Lanthanum-121 | 121La | style="text-align:right" | 57 | style="text-align:right" | 64 | 120.93324(32)# | style="text-align:center" | 1988 | 5.3(2) s | β+ | 121Ba | 11/2−#
|-id=Lanthanum-122 | rowspan=2|122La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 65 | rowspan=2|121.93071(32)# | rowspan=2 style="text-align:center" | 1984 | rowspan=2|8.6(5) s | β+ | 122Ba | rowspan=2|2+ | rowspan=2| | rowspan=2| |- | β+, p (?%) | 121Cs |-id=Lanthanum-123 | 123La | style="text-align:right" | 57 | style="text-align:right" | 66 | 122.92630(21)# | style="text-align:center" | 1978 | 17(3) s | β+ | 123Ba | 11/2−#
|-id=Lanthanum-124 | 124La | style="text-align:right" | 57 | style="text-align:right" | 67 | 123.924574(61) | style="text-align:center" | 1978 | 29.21(17) s | β+ | 124Ba | (7−, 8−)
|-id=Lanthanum-124m | style="text-indent:1em" | 124mLaOrder of ground state and isomer is uncertain. | colspan="3" style="text-indent:2em" | 100(100)# keV | style="text-align:center" | 1997 | 21(4) s | β+ | 124Ba | 2−#
|-id=Lanthanum-125 | 125La | style="text-align:right" | 57 | style="text-align:right" | 68 | 124.920816(28) | style="text-align:center" | 1973 | 64.8(12) s | β+ | 125Ba | 11/2−#
|-id=Lanthanum-125m | style="text-indent:1em" | 125mLa | colspan="3" style="text-indent:2em" | 107.00(10) keV | style="text-align:center" | 1999 | 390(40) ms | IT | 125La | (3/2+)
|-id=Lanthanum-126 | 126La | style="text-align:right" | 57 | style="text-align:right" | 69 | 125.919513(97) | style="text-align:center" | 1961 | 54(2) s | β+ | 126Ba | 5−#
|-id=Lanthanum-126m | style="text-indent:1em" | 126mLa | colspan="3" style="text-indent:2em" | 210(410) keV | style="text-align:center" | 1998 | 20(20) s | β+ | 126Ba | 1−#
|-id=Lanthanum-127 | 127La | style="text-align:right" | 57 | style="text-align:right" | 70 | 126.916375(28) | style="text-align:center" | 1963 | 5.1(1) min | β+ | 127Ba | (11/2−)
|-id=Lanthanum-127m | style="text-indent:1em" | 127mLa | colspan="3" style="text-indent:2em" | 14.2(4) keV | style="text-align:center" | 1973 | 3.7(4) min | β+ | 127Ba | (3/2+)
|-id=Lanthanum-128 | 128La | style="text-align:right" | 57 | style="text-align:right" | 71 | 127.915592(58) | style="text-align:center" | 1961 | 5.18(14) min | β+ | 128Ba | (5+)
|-id=Lanthanum-128m | style="text-indent:1em" | 128mLa | colspan="3" style="text-indent:2em" | 100(100)# keV | style="text-align:center" | 1997 | < 1.4 min | β+ | 128Ba | (1+, 2−)
|-id=Lanthanum-129 | 129La | style="text-align:right" | 57 | style="text-align:right" | 72 | 128.912696(23) | style="text-align:center" | 1963 | 11.6(2) min | β+ | 129Ba | (3/2+)
|-id=Lanthanum-129m | style="text-indent:1em" | 129mLa | colspan="3" style="text-indent:2em" | 172.33(20) keV | style="text-align:center" | 1969 | 560(50) ms | IT | 129La | (11/2−)
|-id=Lanthanum-130 | 130La | style="text-align:right" | 57 | style="text-align:right" | 73 | 129.912369(28) | style="text-align:center" | 1961 | 8.7(1) min | β+ | 130Ba | 3(+)
|-id=Lanthanum-130m | style="text-indent:1em" | 130mLa | colspan="3" style="text-indent:2em" | 214.0(5) keV | style="text-align:center" | 2012 | 742(28) ns | IT | 130La | (5+)
|-id=Lanthanum-131 | 131La | style="text-align:right" | 57 | style="text-align:right" | 74 | 130.910070(30) | style="text-align:center" | 1951 | 59(2) min | β+ | 131Ba | 3/2+
|-id=Lanthanum-131m | style="text-indent:1em" | 131mLa | colspan="3" style="text-indent:2em" | 304.52(24) keV | style="text-align:center" | 1966 | 170(10) μs | IT | 131La | 11/2−
|-id=Lanthanum-132 | 132La | style="text-align:right" | 57 | style="text-align:right" | 75 | 131.910119(39) | style="text-align:center" | 1951 | 4.59(4) h | β+ | 132Ba | 2−
|-id=Lanthanum-132m | rowspan=2 style="text-indent:1em" | 132mLa | rowspan=2 colspan="3" style="text-indent:2em" | 188.20(11) keV | rowspan=2 style="text-align:center" | 1969 | rowspan=2|24.3(5) min | IT (76%) | 132La | rowspan=2|6− | rowspan=2| | rowspan=2| |- | β+ (24%) | 132Ba |-id=Lanthanum-133 | 133La | style="text-align:right" | 57 | style="text-align:right" | 76 | 132.908218(30) | style="text-align:center" | 1950 | 3.912(8) h | β+ | 133Ba | 5/2+
|-id=Lanthanum-134 | 134La | style="text-align:right" | 57 | style="text-align:right" | 77 | 133.908514(21) | style="text-align:center" | 1951 | 6.45(16) min | β+ | 134Ba | 1+
|-id=Lanthanum-134m | style="text-indent:1em" | 134mLa | colspan="3" style="text-indent:2em" | 440(100)# keV | style="text-align:center" | 1985 | 29(4) μs | IT | 134La | (6−)
|-id=Lanthanum-135 | 135La | style="text-align:right" | 57 | style="text-align:right" | 78 | 134.906984(10) | style="text-align:center" | 1948 | 18.91(2) h | β+ | 135Ba | 5/2+
|-id=Lanthanum-136 | 136La | style="text-align:right" | 57 | style="text-align:right" | 79 | 135.907635(57) | style="text-align:center" | 1950 | 9.87(3) min | β+ | 136Ba | 1+
|-id=Lanthanum-136m1 | style="text-indent:1em" | 136m1La | colspan="3" style="text-indent:2em" | 259.5(3) keV | style="text-align:center" | 1966 | 114(5) ms | IT | 136La | (7−)
|-id=Lanthanum-136m2 | style="text-indent:1em" | 136m2La | colspan="3" style="text-indent:2em" | 2520.6(4) keV | style="text-align:center" | 2015 | 187(27) ns | IT | 136La | (14+)
|-id=Lanthanum-137 | 137La | style="text-align:right" | 57 | style="text-align:right" | 80 | 136.9064504(18) | style="text-align:center" | 1948 | 6(2)×104 y | EC | 137Ba | 7/2+
|-id=Lanthanum-137m | style="text-indent:1em" | 137mLa | colspan="3" style="text-indent:2em" | 1869.50(21) keV | style="text-align:center" | 1982 | 342(25) ns | IT | 137La | 19/2−
|-id=Lanthanum-138 | rowspan=2|138LaPrimordial radionuclide | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 81 | rowspan=2|137.90712404(45) | rowspan=2 style="text-align:center" | 1947 | rowspan=2|1.03(1)×1011 y | β+ (65.5%) | 138Ba | rowspan=2|5+ | rowspan=2|8.881(71)×10−4 | rowspan=2| |- | β− (34.5%) | 138Ce |-id=Lanthanum-138m1 | style="text-indent:1em" | 138m1La | colspan="3" style="text-indent:2em" | 72.57(3) keV | style="text-align:center" | 1975 | 116(5) ns | IT | 138La | (3)+
|-id=Lanthanum-138m2 | style="text-indent:1em" | 138m2La | colspan="3" style="text-indent:2em" | 738.80(20) keV | style="text-align:center" | 2014 | 2.0(3) μs | IT | 138La | 7−
|-id=Lanthanum-139 | 139LaFission product | style="text-align:right" | 57 | style="text-align:right" | 82 | 138.90636293(65) | style="text-align:center" | 1924 | colspan=3 align=center|Stable | 7/2+ | 0.9991119(71) | |-id=Lanthanum-139m | style="text-indent:1em" | 139mLa | colspan="3" style="text-indent:2em" | 1800.4(4) keV | style="text-align:center" | 2012 | 315(35) ns | IT | 139La | (17/2+)
|-id=Lanthanum-140 | 140La | style="text-align:right" | 57 | style="text-align:right" | 83 | 139.90948729(65) | style="text-align:center" | 1935 | 40.289(4) h | β− | 140Ce | 3−
|-id=Lanthanum-141 | 141La | style="text-align:right" | 57 | style="text-align:right" | 84 | 140.9109712(44) | style="text-align:center" | 1951 | 3.92(3) h | β− | 141Ce | (7/2+)
|-id=Lanthanum-142 | 142La | style="text-align:right" | 57 | style="text-align:right" | 85 | 141.9140908(67) | style="text-align:center" | 1953 | 91.1(5) min | β− | 142Ce | 2−
|-id=Lanthanum-142m | style="text-indent:1em" | 142mLa | colspan="3" style="text-indent:2em" | 145.82(8) keV | style="text-align:center" | 1983 | 0.87(17) μs | IT | 142La | (4)−
|-id=Lanthanum-143 | 143La | style="text-align:right" | 57 | style="text-align:right" | 86 | 142.9160795(79) | style="text-align:center" | 1951 | 14.2(1) min | β− | 143Ce | (7/2)+
|-id=Lanthanum-144 | 144La | style="text-align:right" | 57 | style="text-align:right" | 87 | 143.919646(14) | style="text-align:center" | 1967 | 44.0(7) s | β− | 144Ce | (3−)
|-id=Lanthanum-145 | 145La | style="text-align:right" | 57 | style="text-align:right" | 88 | 144.921808(13) | style="text-align:center" | 1974 | 24.8(20) s | β− | 145Ce | (5/2+)
|-id=Lanthanum-146 | 146La | style="text-align:right" | 57 | style="text-align:right" | 89 | 145.9256880(18) | style="text-align:center" | 1974 | 9.9(1) s | β− | 146Ce | (5−)
|-id=Lanthanum-146m | style="text-indent:1em" | 146mLa | colspan="3" style="text-indent:2em" | 141.5(24) keV | style="text-align:center" | 1979 | 6.08(22) s | β− | 146Ce | (1−, 2−)
|-id=Lanthanum-147 | rowspan=2|147La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 90 | rowspan=2|146.928418(12) | rowspan=2 style="text-align:center" | 1979 | rowspan=2|4.026(20) s | β− (99.96%) | 147Ce | rowspan=2|(5/2+) | rowspan=2| | rowspan=2| |- | β−, n (0.041%) | 146Ce |-id=Lanthanum-148 | rowspan=2|148La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 91 | rowspan=2|147.932679(21) | rowspan=2 style="text-align:center" | 1982 | rowspan=2|1.414(25) s | β− (99.82%) | 148Ce | rowspan=2|(2−) | rowspan=2| | rowspan=2| |- | β−, n (0.18%) | 147Ce |-id=Lanthanum-149 | rowspan=2|149La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 92 | rowspan=2|148.93535(21) | rowspan=2 style="text-align:center" | 1979 | rowspan=2|1.071(22) s | β− (98.57%) | 149Ce | rowspan=2|(3/2−) | rowspan=2| | rowspan=2| |- | β−, n (1.43%) | 148Ce |-id=Lanthanum-150 | rowspan=2|150La | rowspan=2 style="text-align:right" | 57 | rowspan=2 style="text-align:right" | 93 | rowspan=2|149.9395475(27) | rowspan=2 style="text-align:center" | 1993 | rowspan=2|504(15) ms | β− (97.3%) | 150Ce | rowspan=2|(3+) | rowspan=2| | rowspan=2| |- | β−, n (2.7%) | 149Ce |-id=Lanthanum-151 | 151La