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 (99.911% 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.

Isotopes of lanthanum (₅₇La)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 137La synth 6×104 y ε 137Ba 138La 0.0890% 1.03×1011 y β+ 138Ba β− 138Ce 139La 99.9% stable 140La synth 40.289 h β− 140Ce
Standard atomic weight Ar°(La)
	138.90547±0.00007[2] 138.91±0.01 (abridged)[3]
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Stable Z/N chart of La and Ba

The known isotopes of lanthanum range from ¹¹⁶La to ¹⁵⁵La.

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)
	Excitation energy[n 5]							Normal proportion[1]	Range of variation
116La[5]	57	59	115.95701(35)#	50(22) ms	p (~60%)	115Ba
					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+)
					β+ (6%)	117Ba
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]
					β+, p (?%)	119Cs
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]
					β+, p (?%)	121Cs
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−
					β+ (24%)	132Ba
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
					β− (34.5%)	138Ce
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+)
					β−, n (0.041%)	146Ce
148La	57	91	147.932679(21)	1.414(25) s	β− (99.82%)	148Ce	(2−)
					β−, n (0.18%)	147Ce
149La	57	92	148.93535(21)	1.071(22) s	β− (98.57%)	149Ce	(3/2−)
					β−, n (1.43%)	148Ce
150La	57	93	149.9395475(27)	504(15) ms	β− (97.3%)	150Ce	(3+)
					β−, n (2.7%)	149Ce
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

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. Order of ground state and isomer is uncertain.
11. Primordial radionuclide
12. Fission product

See also

Daughter products other than lanthanum

• Isotopes of cerium
• Isotopes of barium
• Isotopes of caesium