Isotopes of lanthanum

Isotopes of lanthanum (₅₇La)
β−	138Ce
Standard atomic weight Ar°(La)
	138.90547±0.00007; 138.91±0.01 (abridged);
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Last updated July 26, 2025

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.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[4] ^{[n 2]}^{[n 3]}	Half-life ^[1] ^{[n 4]}^{[n 5]}	Decay mode ^[1] ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity ^[1] ^{[n 9]}^{[n 5]}	Natural abundance (mole fraction)
Nuclide ^{[n 1]}	Excitation energy^{[n 5]}			Half-life ^[1] ^{[n 4]}^{[n 5]}	Decay mode ^[1] ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity ^[1] ^{[n 9]}^{[n 5]}	Normal proportion^[1]	Range of variation
¹¹⁶La^[5]	57	59	115.95701(35)#	50(22) ms	p (~60%)	¹¹⁵Ba
¹¹⁶La^[5]	57	59	115.95701(35)#	50(22) ms	β⁺ (~40%)	¹¹⁶Ba
^116mLa^[5]	182 keV			2.0+2.8 −0.8 μs	IT	¹¹⁶La
¹¹⁷La^[5]	57	60	116.95033(22)#	21.6(31) ms	p (94%)	¹¹⁶Ba	(3/2+)
¹¹⁷La^[5]	57	60	116.95033(22)#	21.6(31) ms	β⁺ (6%)	¹¹⁷Ba	(3/2+)
^117mLa^[5]	192 keV			3.9+1.9 −0.9 μs	IT	¹¹⁷La	(7/2−)
¹²⁰La	57	63	119.93820(32)#	2.8(2) s	β⁺	¹²⁰Ba	4+^[6]
¹²⁰La	57	63	119.93820(32)#	2.8(2) s	β⁺, p (?%)	¹¹⁹Cs	4+^[6]
¹²¹La	57	64	120.93324(32)#	5.3(2) s	β⁺	¹²¹Ba	11/2−#
¹²²La	57	65	121.93071(32)#	8.6(5) s	β⁺	¹²²Ba	2+^[6]
¹²²La	57	65	121.93071(32)#	8.6(5) s	β⁺, p (?%)	¹²¹Cs	2+^[6]
¹²³La	57	66	122.92630(21)#	17(3) s	β⁺	¹²³Ba	11/2−#
¹²⁴La	57	67	123.924574(61)	29.21(17) s	β⁺	¹²⁴Ba	(7−, 8−)
^124mLa^{[n 10]}	100(100)# keV			21(4) s	β⁺	¹²⁴Ba	2−#
¹²⁵La	57	68	124.920816(28)	64.8(12) s	β⁺	¹²⁵Ba	11/2−#
^125mLa	107.00(10) keV			390(40) ms	IT	¹²⁵La	(3/2+)
¹²⁶La	57	69	125.919513(97)	54(2) s	β⁺	¹²⁶Ba	5−#
^126mLa^{[n 10]}	210(410) keV			20(20) s	β⁺	¹²⁶Ba	1−#
¹²⁷La	57	70	126.916375(28)	5.1(1) min	β⁺	¹²⁷Ba	(11/2−)
^127mLa	14.2(4) keV			3.7(4) min	β⁺	¹²⁷Ba	(3/2+)
¹²⁸La	57	71	127.915592(58)	5.18(14) min	β⁺	¹²⁸Ba	(5+)
^128mLa^{[n 10]}	100(100)# keV			< 1.4 min	β⁺	¹²⁸Ba	(1+, 2−)
¹²⁹La	57	72	128.912696(23)	11.6(2) min	β⁺	¹²⁹Ba	(3/2+)
^129mLa	172.33(20) keV			560(50) ms	IT	¹²⁹La	(11/2−)
¹³⁰La	57	73	129.912369(28)	8.7(1) min	β⁺	¹³⁰Ba	3(+)
^130mLa	214.0(5) keV			742(28) ns	IT	¹³⁰La	(5+)
¹³¹La	57	74	130.910070(30)	59(2) min	β⁺	¹³¹Ba	3/2+
^131mLa	304.52(24) keV			170(10) μs	IT	¹³¹La	11/2−
¹³²La	57	75	131.910119(39)	4.59(4) h	β⁺	¹³²Ba	2−
^132mLa	188.20(11) keV			24.3(5) min	IT (76%)	¹³²La	6−
^132mLa	188.20(11) keV			24.3(5) min	β⁺ (24%)	¹³²Ba	6−
¹³³La	57	76	132.908218(30)	3.912(8) h	β⁺	¹³³Ba	5/2+
¹³⁴La	57	77	133.908514(21)	6.45(16) min	β⁺	¹³⁴Ba	1+
^134mLa	440(100)# keV			29(4) μs	IT	¹³⁴La	(6−)
¹³⁵La	57	78	134.906984(10)	18.91(2) h	β⁺	¹³⁵Ba	5/2+
¹³⁶La	57	79	135.907635(57)	9.87(3) min	β⁺	¹³⁶Ba	1+
^136m1La	259.5(3) keV			114(5) ms	IT	¹³⁶La	(7−)
^136m2La	2520.6(4) keV			187(27) ns	IT	¹³⁶La	(14+)
¹³⁷La	57	80	136.9064504(18)	6(2)×10⁴ y	EC	¹³⁷Ba	7/2+
^137mLa	1869.50(21) keV			342(25) ns	IT	¹³⁷La	19/2−
¹³⁸La^{[n 11]}	57	81	137.90712404(45)	1.03(1)×10¹¹ y	β⁺ (65.5%)	¹³⁸Ba	5+	8.881(71)×10⁻⁴
¹³⁸La^{[n 11]}	57	81	137.90712404(45)	1.03(1)×10¹¹ y	β⁻ (34.5%)	¹³⁸Ce	5+	8.881(71)×10⁻⁴
^138m1La	72.57(3) keV			116(5) ns	IT	¹³⁸La	(3)+
^138m2La	738.80(20) keV			2.0(3) μs	IT	¹³⁸La	7−
¹³⁹La^{[n 12]}	57	82	138.90636293(65)	Stable			7/2+	0.9991119(71)
^139mLa	1800.4(4) keV			315(35) ns	IT	¹³⁹La	(17/2+)
¹⁴⁰La^{[n 12]}	57	83	139.90948729(65)	40.289(4) h	β⁻	¹⁴⁰Ce	3−
¹⁴¹La	57	84	140.9109712(44)	3.92(3) h	β⁻	¹⁴¹Ce	(7/2+)
¹⁴²La	57	85	141.9140908(67)	91.1(5) min	β⁻	¹⁴²Ce	2−
^142mLa	145.82(8) keV			0.87(17) μs	IT	¹⁴²La	(4)−
¹⁴³La	57	86	142.9160795(79)	14.2(1) min	β⁻	¹⁴³Ce	(7/2)+
¹⁴⁴La	57	87	143.919646(14)	44.0(7) s	β⁻	¹⁴⁴Ce	(3−)
¹⁴⁵La	57	88	144.921808(13)	24.8(20) s	β⁻	¹⁴⁵Ce	(5/2+)
¹⁴⁶La	57	89	145.9256880(18)	9.9(1) s	β⁻	¹⁴⁶Ce	(5−)
^146mLa	141.5(24) keV			6.08(22) s	β⁻	¹⁴⁶Ce	(1−, 2−)
¹⁴⁷La	57	90	146.928418(12)	4.026(20) s	β⁻ (99.96%)	¹⁴⁷Ce	(5/2+)
¹⁴⁷La	57	90	146.928418(12)	4.026(20) s	β⁻, n (0.041%)	¹⁴⁶Ce	(5/2+)
¹⁴⁸La	57	91	147.932679(21)	1.414(25) s	β⁻ (99.82%)	¹⁴⁸Ce	(2−)
¹⁴⁸La	57	91	147.932679(21)	1.414(25) s	β⁻, n (0.18%)	¹⁴⁷Ce	(2−)
¹⁴⁹La	57	92	148.93535(21)	1.071(22) s	β⁻ (98.57%)	¹⁴⁹Ce	(3/2−)
¹⁴⁹La	57	92	148.93535(21)	1.071(22) s	β⁻, n (1.43%)	¹⁴⁸Ce	(3/2−)
¹⁵⁰La	57	93	149.9395475(27)	504(15) ms	β⁻ (97.3%)	¹⁵⁰Ce	(3+)
¹⁵⁰La	57	93	149.9395475(27)	504(15) ms	β⁻, n (2.7%)	¹⁴⁹Ce	(3+)
¹⁵¹La	57	94	150.94277(47)	465(24) ms	β⁻	¹⁵¹Ce	1/2+#
¹⁵²La	57	95	151.94709(32)#	287(16) ms	β⁻	¹⁵²Ce	2−#
¹⁵³La	57	96	152.95055(32)#	245(18) ms	β⁻	¹⁵³Ce	1/2+#
¹⁵⁴La	57	97	153.95542(32)#	161(15) ms	β⁻	¹⁵⁴Ce	2−#
¹⁵⁵La	57	98	154.95928(43)#	101(28) ms	β⁻	¹⁵⁵Ce	1/2+#
¹⁵⁶La	57	99	155.96452(43)#	84(78) ms	β⁻	¹⁵⁶Ce	4+#
¹⁵⁷La	57	100	156.96879(32)#	30# ms [> 550 ns]			1/2+#
This table header & footer: view

↑ ^mLa – 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

References

1 2 3 4 5 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
↑ "Standard Atomic Weights: Lanthanum". CIAAW. 2005.
↑ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
↑ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
1 2 3 4 Zhang, Wei; Cederwall, Bo; Aktas, Özge; Liu, Xiaoyu; Ertoprak, Aysegül; Nyberg, Ayse; Auranen, Kalle; Alayed, Betool; Badran, Hussam; Boston, Helen; Doncel, Maria; Forsberg, Ulrika; Grahn, Tuomas; Greenlees, Paul T.; Guo, Song; Heery, Jacob; Hilton, Joshua; Jenkins, David; Julin, Rauno; Juutinen, Sakari; Luoma, Minna; Neuvonen, Olavi; Ojala, Joonas; Page, Robert D.; Pakarinen, Janne; Partanen, Jari; Paul, Edward S.; Petrache, Costel; Rahkila, Panu; Ruotsalainen, Panu; Sandzelius, Mikael; Sarén, Jan; Szwec, Stuart; Tann, Holly; Uusitalo, Juha; Wadsworth, Robert (14 November 2022). "Observation of the proton emitter ¹¹⁶
₅₇La^₅₉" (PDF). Communications Physics. 5 (1): 1–8. doi: 10.1038/s42005-022-01069-w . ISSN 2399-3650. S2CID 253512231.
1 2 Jodidar, P.M.; Petrache, C.M.; Lv, B.F.; Lawrie, E.A.; Astier, A.; Guo, S.; Zheng, K.K.; Auranen, K.; Briscoe, A.D.; Grahn, T.; Greenlees, P.T.; Illana, A.; Joukainen, H.; Julin, R.; Louko, J.; Luoma, M.; Jutila, H.; Ojala, J.; Pakarinen, J.; Plaza, A.M.; Rahkila, P.; Ruotsalainen, P.; Sarén, J.; Tolosa-Delgado, A.; Uusitalo, J.; Zimba, G.; Kuti, I.; Krakó, A.; Andreoiu, C.; Joss, D.T.; Page, R.D.; Cederlöf, E.A.; Ertoprak, A. (August 2024). "First observation of excited states in 120La and its impact on the shape evolution in the A ≈ 120 mass region" (PDF). Physics Letters B. 855: 138806. doi:10.1016/j.physletb.2024.138806.

Isotope masses from:
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
Isotopic compositions and standard atomic masses from:
- de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry . 75 (6): 683–800. doi: 10.1351/pac200375060683 .
- Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry . 78 (11): 2051–2066. doi: 10.1351/pac200678112051 .
"News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
Half-life, spin, and isomer data selected from the following sources.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- National Nuclear Data Center. "NuDat 3.0 database". Brookhaven National Laboratory.

- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.

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[4] La – Excited nuclear isomer.

[6] ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.

[TMS-7] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[8] Bold half-life – nearly stable, half-life longer than age of universe.

[TNN-9] 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[10] Modes of decay:
EC: Electron capture
IT: Isomeric transition
n: Neutron emission
p: Proton emission

[11] Bold italics symbol as daughter – Daughter product is nearly stable.

[12] Bold symbol as daughter – Daughter product is stable.

[13] ( ) spin value – Indicates spin with weak assignment arguments.

[order-16] 1 2 3 Order of ground state and isomer is uncertain.

[17] Primordial radionuclide

[FP-18] 1 2 Fission product

[NUBASE2020-1] 1 2 3 4 5 Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[CIAAWlanthanum-2] "Standard Atomic Weights: Lanthanum". CIAAW. 2005.

[CIAAW2021-3] Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

[AME2020_II-5] Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.

[zhang2022-14] 1 2 3 4 Zhang, Wei; Cederwall, Bo; Aktas, Özge; Liu, Xiaoyu; Ertoprak, Aysegül; Nyberg, Ayse; Auranen, Kalle; Alayed, Betool; Badran, Hussam; Boston, Helen; Doncel, Maria; Forsberg, Ulrika; Grahn, Tuomas; Greenlees, Paul T.; Guo, Song; Heery, Jacob; Hilton, Joshua; Jenkins, David; Julin, Rauno; Juutinen, Sakari; Luoma, Minna; Neuvonen, Olavi; Ojala, Joonas; Page, Robert D.; Pakarinen, Janne; Partanen, Jari; Paul, Edward S.; Petrache, Costel; Rahkila, Panu; Ruotsalainen, Panu; Sandzelius, Mikael; Sarén, Jan; Szwec, Stuart; Tann, Holly; Uusitalo, Juha; Wadsworth, Robert (14 November 2022). "Observation of the proton emitter ¹¹⁶
₅₇La^₅₉" (PDF). Communications Physics. 5 (1): 1–8. doi: 10.1038/s42005-022-01069-w . ISSN 2399-3650. S2CID 253512231.

[jodidar2024-15] 1 2 Jodidar, P.M.; Petrache, C.M.; Lv, B.F.; Lawrie, E.A.; Astier, A.; Guo, S.; Zheng, K.K.; Auranen, K.; Briscoe, A.D.; Grahn, T.; Greenlees, P.T.; Illana, A.; Joukainen, H.; Julin, R.; Louko, J.; Luoma, M.; Jutila, H.; Ojala, J.; Pakarinen, J.; Plaza, A.M.; Rahkila, P.; Ruotsalainen, P.; Sarén, J.; Tolosa-Delgado, A.; Uusitalo, J.; Zimba, G.; Kuti, I.; Krakó, A.; Andreoiu, C.; Joss, D.T.; Page, R.D.; Cederlöf, E.A.; Ertoprak, A. (August 2024). "First observation of excited states in 120La and its impact on the shape evolution in the A ≈ 120 mass region" (PDF). Physics Letters B. 855: 138806. doi:10.1016/j.physletb.2024.138806.

[1]

[2]

[3]

[n 1]

[4]

[n 2]

[n 3]

[n 4]

[n 5]

[n 6]

[n 7]

[n 8]

[n 9]

[5]

[6]

[n 10]

[n 11]

[n 12]

Isotopes of lanthanum

Contents

List of isotopes

See also

References

EC:	Electron capture
IT:	Isomeric transition
n:	Neutron emission
p:	Proton emission