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Naturally occurring lanthanum (57La) is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). There are 38 radioisotopes that have been characterized, with the most stable being 138La, with a half-life of 1.02×1011 years; 137La, with a half-life of 60,000 years and 140La, 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 132mLa, with a half-life of 24.3 minutes.
The isotopes of lanthanum range in atomic weight from 116.95 atomic mass unit, u (117La) to 154.96 u (155La).
Naturally occurring lanthanum (57La) is composed of one stable (139La) and one radioactive (138La) isotope, with the stable isotope, 139La, being the most abundant (99.91% natural abundance). There are 38 radioisotopes that have been characterized, with the most stable being 138La, with a half-life of 1.02×1011 years; 137La, with a half-life of 60,000 years and 140La, 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 132mLa, with a half-life of 24.3 minutes.
The isotopes of lanthanum range in atomic weight from 116.95 atomic mass unit, u (117La) to 154.96 u (155La).
List of isotopes
, - , rowspan=2, 117La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 60 , rowspan=2, 116.95007(43)# , rowspan=2, 23.5(26) ms , beta decay, β+ , 117Ba , rowspan=2, (3/2+, 3/2−) , rowspan=2, , rowspan=2, , - , proton emission, p , 116Ba , - , style="text-indent:1em" , 117mLa , colspan="3" style="text-indent:2em" , 151(12) keV , 10(5) ms , , , (9/2+) , , , - , 118La , style="text-align:right" , 57 , style="text-align:right" , 61 , 117.94673(32)# , 200# ms , β+ , 118Ba , , , , - , 119La , style="text-align:right" , 57 , style="text-align:right" , 62 , 118.94099(43)# , 1# s , β+ , 119Ba , 11/2−# , , , - , rowspan=2, 120La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 63 , rowspan=2, 119.93807(54)# , rowspan=2, 2.8(2) s , β+ , 120Ba , rowspan=2, , rowspan=2, , rowspan=2, , - , β+, p , 119Cs , - , rowspan=2, 121La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 64 , rowspan=2, 120.93301(54)# , rowspan=2, 5.3(2) s , β+ , 121Ba , rowspan=2, 11/2−# , rowspan=2, , rowspan=2, , - , β+, p , 120Cs , - , rowspan=2, 122La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 65 , rowspan=2, 121.93071(32)# , rowspan=2, 8.6(5) s , β+ , 122Ba , rowspan=2, , rowspan=2, , rowspan=2, , - , β+, p , 121Cs , - , 123La , style="text-align:right" , 57 , style="text-align:right" , 66 , 122.92624(21)# , 17(3) s , β+ , 123Ba , 11/2−# , , , - , 124La , style="text-align:right" , 57 , style="text-align:right" , 67 , 123.92457(6) , 29.21(17) s , β+ , 124Ba , (7−, 8−) , , , - , style="text-indent:1em" , 124mLa , colspan="3" style="text-indent:2em" , 100(100)# keV , 21(4) s , , , low(+#) , , , - , 125La , style="text-align:right" , 57 , style="text-align:right" , 68 , 124.920816(28) , 64.8(12) s , β+ , 125Ba , (11/2−) , , , - , style="text-indent:1em" , 125mLa , colspan="3" style="text-indent:2em" , 107.0(10) keV , 390(40) ms , , , (3/2+) , , , - , 126La , style="text-align:right" , 57 , style="text-align:right" , 69 , 125.91951(10) , 54(2) s , β+ , 126Ba , (5)(+#) , , , - , style="text-indent:1em" , 126mLa , colspan="3" style="text-indent:2em" , 210(410) keV , 20(20) s , , , (0−, 1−, 2−) , , , - , 127La , style="text-align:right" , 57 , style="text-align:right" , 70 , 126.916375(28) , 5.1(1) min , β+ , 127Ba , (11/2−) , , , - , rowspan=2 style="text-indent:1em" , 127mLa , rowspan=2 colspan="3" style="text-indent:2em" , 14.8(12) keV , rowspan=2, 3.7(4) min , β+ , 127Ba , rowspan=2, (3/2+) , rowspan=2, , rowspan=2, , - , Isomeric transition, IT , 127La , - , 128La , style="text-align:right" , 57 , style="text-align:right" , 71 , 127.91559(6) , 5.18(14) min , β+ , 128Ba , (5+) , , , - , style="text-indent:1em" , 128mLa , colspan="3" style="text-indent:2em" , 100(100)# keV , <1.4 min , IT , 128La , (1+, 2−) , , , - , 129La , style="text-align:right" , 57 , style="text-align:right" , 72 , 128.912693(22) , 11.6(2) min , β+ , 129Ba , 3/2+ , , , - , style="text-indent:1em" , 129mLa , colspan="3" style="text-indent:2em" , 172.1(4) keV , 560(50) ms , IT , 129La , 11/2− , , , - , 130La , style="text-align:right" , 57 , style="text-align:right" , 73 , 129.912369(28) , 8.7(1) min , β+ , ''130Ba'' , 3(+) , , , - , 131La , style="text-align:right" , 57 , style="text-align:right" , 74 , 130.91007(3) , 59(2) min , β+ , 131Ba , 3/2+ , , , - , style="text-indent:1em" , 131mLa , colspan="3" style="text-indent:2em" , 304.52(24) keV , 170(10) μs , , , 11/2− , , , - , 132La , style="text-align:right" , 57 , style="text-align:right" , 75 , 131.91010(4) , 4.8(2) h , β+ , 132Ba , 2− , , , - , rowspan=2 style="text-indent:1em" , 132mLa , rowspan=2 colspan="3" style="text-indent:2em" , 188.18(11) keV , rowspan=2, 24.3(5) min , IT (76%) , 132La , rowspan=2, 6− , rowspan=2, , rowspan=2, , - , β+ (24%) , 132Ba , - , 133La , style="text-align:right" , 57 , style="text-align:right" , 76 , 132.90822(3) , 3.912(8) h , β+ , 133Ba , 5/2+ , , , - , 134La , style="text-align:right" , 57 , style="text-align:right" , 77 , 133.908514(21) , 6.45(16) min , β+ , 134Ba , 1+ , , , - , 135La , style="text-align:right" , 57 , style="text-align:right" , 78 , 134.906977(11) , 19.5(2) h , β+ , 135Ba , 5/2+ , , , - , 136La , style="text-align:right" , 57 , style="text-align:right" , 79 , 135.90764(6) , 9.87(3) min , β+ , 136Ba , 1+ , , , - , style="text-indent:1em" , 136mLa , colspan="3" style="text-indent:2em" , 255(9) keV , 114(3) ms , IT , 136La , (8)(−#) , , , - , 137La , style="text-align:right" , 57 , style="text-align:right" , 80 , 136.906494(14) , 6(2)×104 y , Electron capture, EC , 137Ba , 7/2+ , , , Extinct radionuclide, extinct , - , rowspan=2, 138Laprimordial nuclide, Primordial radionuclide , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 81 , rowspan=2, 137.907112(4) , rowspan=2, 1.02(1)×1011 y , β+ (66.4%) , 138Ba , rowspan=2, 5+ , rowspan=2, 9.0(1)×10−4 , rowspan=2, , - , β− (33.6%) , 138Ce , - , style="text-indent:1em" , 138mLa , colspan="3" style="text-indent:2em" , 72.57(3) keV , 116(5) ns , , , (3)+ , , , - , 139LaFission product , style="text-align:right" , 57 , style="text-align:right" , 82 , 138.9063533(26) , colspan=3 align=center, StableTheoretically capable of spontaneous fission , 7/2+ , 0.99910(1) , , - , 140La , style="text-align:right" , 57 , style="text-align:right" , 83 , 139.9094776(26) , 1.6781(3) d , β− , 140Ce , 3− , , , - , 141La , style="text-align:right" , 57 , style="text-align:right" , 84 , 140.910962(5) , 3.92(3) h , β− , 141Ce , (7/2+) , , , - , 142La , style="text-align:right" , 57 , style="text-align:right" , 85 , 141.914079(6) , 91.1(5) min , β− , 142Ce , 2− , , , - , 143La , style="text-align:right" , 57 , style="text-align:right" , 86 , 142.916063(17) , 14.2(1) min , β− , 143Ce , (7/2)+ , , , - , 144La , style="text-align:right" , 57 , style="text-align:right" , 87 , 143.91960(5) , 40.8(4) s , β− , 144Ce , (3−) , , , - , 145La , style="text-align:right" , 57 , style="text-align:right" , 88 , 144.92165(10) , 24.8(20) s , β− , 145Ce , (5/2+) , , , - , rowspan=2, 146La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 89 , rowspan=2, 145.92579(8) , rowspan=2, 6.27(10) s , β− (99.99%) , 146Ce , rowspan=2, 2− , rowspan=2, , rowspan=2, , - , β−, neutron, n (.007%) , 145Ce , - , style="text-indent:1em" , 146mLa , colspan="3" style="text-indent:2em" , 130(130) keV , 10.0(1) s , β− , 146Ce , (6−) , , , - , rowspan=2, 147La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 90 , rowspan=2, 146.92824(5) , rowspan=2, 4.015(8) s , β− (99.96%) , 147Ce , rowspan=2, (5/2+) , rowspan=2, , rowspan=2, , - , β−, n (.04%) , 146Ce , - , rowspan=2, 148La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 91 , rowspan=2, 147.93223(6) , rowspan=2, 1.26(8) s , β− (99.85%) , 148Ce , rowspan=2, (2−) , rowspan=2, , rowspan=2, , - , β−, n (.15%) , 147Ce , - , rowspan=2, 149La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 92 , rowspan=2, 148.93473(34)# , rowspan=2, 1.05(3) s , β− (98.6%) , 149Ce , rowspan=2, 5/2+# , rowspan=2, , rowspan=2, , - , β−, n (1.4%) , 148Ce , - , rowspan=2, 150La , rowspan=2 style="text-align:right" , 57 , rowspan=2 style="text-align:right" , 93 , rowspan=2, 149.93877(43)# , rowspan=2, 510(30) ms , β− (97.3%) , 150Ce , rowspan=2, (3+) , rowspan=2, , rowspan=2, , - , β−, n (2.7%) , 149Ce , - , 151La , style="text-align:right" , 57 , style="text-align:right" , 94 , 150.94172(43)# , 300# ms [>300 ns] , β− , 151Ce , 5/2+# , , , - , 152La , style="text-align:right" , 57 , style="text-align:right" , 95 , 151.94625(43)# , 200# ms [>300 ns] , β− , 152Ce , , , , - , 153La , style="text-align:right" , 57 , style="text-align:right" , 96 , 152.94962(64)# , 150# ms [>300 ns] , β− , 153Ce , 5/2+# , , , - , 154La , style="text-align:right" , 57 , style="text-align:right" , 97 , 153.95450(64)# , 100# ms , β− , 154Ce , , , , - , 155La , style="text-align:right" , 57 , style="text-align:right" , 98 , 154.95835(86)# , 60# ms , β− , 155Ce , 5/2+# , ,References