Isotopes of lanthanum

Naturally occurring lanthanum (La) 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 102×10⁹ 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 u (¹¹⁷La) to 154.96 u (¹⁵⁵La).

Relative atomic mass: 138.90547(7).

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life[n 1]	decay mode(s)[1][n 2]	daughter isotope(s)[n 3]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^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 4]	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 5]	57	82	138.9063533(26)	Stable[n 6]			7/2+	0.99910(1)
^140La[n 5]	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. Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
2. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
3. Bold for stable isotopes, bold italics for near-stable isotopes (half-life longer than the age of the universe)
4. Primordial radionuclide
5. Fission product
6. Theoretically capable of spontaneous fission

Notes

• Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

1. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). 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:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (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. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.