Isotopes of lanthanum

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.

Main isotopes of lanthanum (₅₇La)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^137La syn 6×10^4 y ε ^137Ba ^138La 0.089% 1.05×10^11 y ε ^138Ba β^− ^138Ce ^139La 99.911% stable
Standard atomic weight Ar, standard(La)	138.90547(7)[1]

Stable Z/N chart of La and Ba

The isotopes of lanthanum range in atomic weight from 116.95 u (¹¹⁷La) to 154.96 u (¹⁵⁵La).

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4][n 5]	Decay mode [n 6]	Daughter isotope [n 7][n 8]	Spin and parity [n 9][n 5]	Natural abundance (mole fraction)
	Excitation energy[n 5]							Normal proportion	Range of variation
^117La	57	60	116.95007(43)#	23.5(26) ms	β^+	^117Ba	(3/2+, 3/2−)
					p	^116Ba
^117mLa	151(12) keV			10(5) ms			(9/2+)
^118La	57	61	117.94673(32)#	200# ms	β^+	^118Ba
^119La	57	62	118.94099(43)#	1# s	β^+	^119Ba	11/2−#
^120La	57	63	119.93807(54)#	2.8(2) s	β^+	^120Ba
					β^+, p	^119Cs
^121La	57	64	120.93301(54)#	5.3(2) s	β^+	^121Ba	11/2−#
					β^+, p	^120Cs
^122La	57	65	121.93071(32)#	8.6(5) s	β^+	^122Ba
					β^+, p	^121Cs
^123La	57	66	122.92624(21)#	17(3) s	β^+	^123Ba	11/2−#
^124La	57	67	123.92457(6)	29.21(17) s	β^+	^124Ba	(7−, 8−)
^124mLa	100(100)# keV			21(4) s			low(+#)
^125La	57	68	124.920816(28)	64.8(12) s	β^+	^125Ba	(11/2−)
^125mLa	107.0(10) keV			390(40) ms			(3/2+)
^126La	57	69	125.91951(10)	54(2) s	β^+	^126Ba	(5)(+#)
^126mLa	210(410) keV			20(20) s			(0−, 1−, 2−)
^127La	57	70	126.916375(28)	5.1(1) min	β^+	^127Ba	(11/2−)
^127mLa	14.8(12) keV			3.7(4) min	β^+	^127Ba	(3/2+)
					IT	^127La
^128La	57	71	127.91559(6)	5.18(14) min	β^+	^128Ba	(5+)
^128mLa	100(100)# keV			<1.4 min	IT	^128La	(1+, 2−)
^129La	57	72	128.912693(22)	11.6(2) min	β^+	^129Ba	3/2+
^129mLa	172.1(4) keV			560(50) ms	IT	^129La	11/2−
^130La	57	73	129.912369(28)	8.7(1) min	β^+	^130Ba	3(+)
^131La	57	74	130.91007(3)	59(2) min	β^+	^131Ba	3/2+
^131mLa	304.52(24) keV			170(10) µs			11/2−
^132La	57	75	131.91010(4)	4.8(2) h	β^+	^132Ba	2−
^132mLa	188.18(11) keV			24.3(5) min	IT (76%)	^132La	6−
					β^+ (24%)	^132Ba
^133La	57	76	132.90822(3)	3.912(8) h	β^+	^133Ba	5/2+
^134La	57	77	133.908514(21)	6.45(16) min	β^+	^134Ba	1+
^135La	57	78	134.906977(11)	19.5(2) h	β^+	^135Ba	5/2+
^136La	57	79	135.90764(6)	9.87(3) min	β^+	^136Ba	1+
^136mLa	255(9) keV			114(3) ms	IT	^136La	(8)(−#)
^137La	57	80	136.906494(14)	6(2)×10^4 y	EC	^137Ba	7/2+
^138La[n 10]	57	81	137.907112(4)	1.02(1)×10^11 y	β^+ (66.4%)	^138Ba	5+	9.0(1)×10^−4
					β^− (33.6%)	^138Ce
^138mLa	72.57(3) keV			116(5) ns			(3)+
^139La[n 11]	57	82	138.9063533(26)	Stable			7/2+	0.99910(1)
^140La[n 11]	57	83	139.9094776(26)	1.6781(3) d	β^−	^140Ce	3−
^141La	57	84	140.910962(5)	3.92(3) h	β^−	^141Ce	(7/2+)
^142La	57	85	141.914079(6)	91.1(5) min	β^−	^142Ce	2−
^143La	57	86	142.916063(17)	14.2(1) min	β^−	^143Ce	(7/2)+
^144La	57	87	143.91960(5)	40.8(4) s	β^−	^144Ce	(3−)
^145La	57	88	144.92165(10)	24.8(20) s	β^−	^145Ce	(5/2+)
^146La	57	89	145.92579(8)	6.27(10) s	β^− (99.99%)	^146Ce	2−
					β^−, n (.007%)	^145Ce
^146mLa	130(130) keV			10.0(1) s	β^−	^146Ce	(6−)
^147La	57	90	146.92824(5)	4.015(8) s	β^− (99.96%)	^147Ce	(5/2+)
					β^−, n (.04%)	^146Ce
^148La	57	91	147.93223(6)	1.26(8) s	β^− (99.85%)	^148Ce	(2−)
					β^−, n (.15%)	^147Ce
^149La	57	92	148.93473(34)#	1.05(3) s	β^− (98.6%)	^149Ce	5/2+#
					β^−, n (1.4%)	^148Ce
^150La	57	93	149.93877(43)#	510(30) ms	β^− (97.3%)	^150Ce	(3+)
					β^−, n (2.7%)	^149Ce
^151La	57	94	150.94172(43)#	300# ms [>300 ns]	β^−	^151Ce	5/2+#
^152La	57	95	151.94625(43)#	200# ms [>300 ns]	β^−	^152Ce
^153La	57	96	152.94962(64)#	150# ms [>300 ns]	β^−	^153Ce	5/2+#
^154La	57	97	153.95450(64)#	100# ms	β^−	^154Ce
^155La	57	98	154.95835(86)#	60# ms	β^−	^155Ce	5/2+#

1. ^mLa – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

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

7. Bold italics symbol as daughter – Daughter product is nearly stable.
8. Bold symbol as daughter – Daughter product is stable.
9. ( ) spin value – Indicates spin with weak assignment arguments.
10. Primordial radionuclide
11. Fission product

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.

• 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. Lay summary.
• 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 2.x 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.