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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.

Main isotopes of lanthanum (57La)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
137La syn 6×104 y ε 137Ba
138La 0.089% 1.05×1011 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 isotopesEdit

Nuclide
[n 1]
Z N Isotopic mass (u)
[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)×104 y EC 137Ba 7/2+
138La[n 10] 57 81 137.907112(4) 1.02(1)×1011 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. ^ a b c # – 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. ^ a b Fission product

ReferencesEdit

  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.