# Isotopes of gadolinium

Naturally occurring gadolinium ($_{64}$Gd) is composed of 6 stable isotopes, $^{154}$Gd, $^{155}$Gd, $^{156}$Gd, $^{157}$Gd, $^{158}$Gd and $^{160}$Gd, and 1 radioisotope, $^{152}$Gd, with $^{158}$Gd being the most abundant (24.84% natural abundance). The predicted double beta decay of $^{160}$Gd has never been observed; only a lower limit on its half-life of more than 1.3×10$^{21}$ years has been set experimentally.
Thirty-three radioisotopes have been characterized, with the most stable being alpha-decaying $^{152}$Gd (naturally occurring) with a half-life of 1.08×10$^{14}$ years, and $^{150}$Gd with a half-life of 1.79×10$^6$ years. All of the remaining radioactive isotopes have half-lives less than 100 years, the majority of these having half-lives less than 24.6 seconds. Gadolinium isotopes have 10 metastable isomers, with the most stable being $^{143m}$Gd (t$_{1/2}$ = 110 seconds), $^{145m}$Gd (t$_{1/2}$ = 85 seconds) and $^{141m}$Gd (t$_{1/2}$ = 24.5 seconds).
The primary decay mode at atomic weights lower than the most abundant stable isotope, $^{158}$Gd, is electron capture, and the primary mode at higher atomic weights is beta decay. The primary decay products for isotopes lighter than $^{158}$Gd are isotopes of europium and the primary products of heavier isotopes are isotopes of terbium.

## List of isotopes

| Nuclide | Z | N | Isotopic mass (Da) | Half-life | Decay mode | Daughter isotope | Spin and parity | Natural abundance (mole fraction) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{135}$Gd | 64 | 71 | 134.95250(43)# | 1.1(2) s | β$^+$ (98%) | $^{135}$Eu | (5/2+) | | |
| $^{135}$Gd | 64 | 71 | 134.95250(43)# | 1.1(2) s | β$^+$, p (98%) | $^{134}$Sm | (5/2+) | | |
| $^{136}$Gd | 64 | 72 | 135.94730(32)# | 1# s [>200 ns] | β$^+$? | $^{136}$Eu | 0+ | | |
| $^{136}$Gd | 64 | 72 | 135.94730(32)# | 1# s [>200 ns] | β$^+$, p? | $^{135}$Sm | 0+ | | |
| $^{137}$Gd | 64 | 73 | 136.94502(32)# | 2.2(2) s | β$^+$ | $^{137}$Eu | (7/2)+# | | |
| $^{137}$Gd | 64 | 73 | 136.94502(32)# | 2.2(2) s | β$^+$, p? | $^{136}$Sm | (7/2)+# | | |
| $^{138}$Gd | 64 | 74 | 137.94025(22)# | 4.7(9) s | β$^+$ | $^{138}$Eu | 0+ | | |
| $^{138m}$Gd | 2232.6(11) keV | 2232.6(11) keV | 2232.6(11) keV | 6.2(0.2) μs | IT | $^{138}$Gd | (8−) | | |
| $^{139}$Gd | 64 | 75 | 138.93813(21)# | 5.7(3) s | β$^+$ | $^{139}$Eu | 9/2−# | | |
| $^{139}$Gd | 64 | 75 | 138.93813(21)# | 5.7(3) s | β$^+$, p? | $^{138}$Sm | 9/2−# | | |
| $^{139m}$Gd | 250(150)# keV | 250(150)# keV | 250(150)# keV | 4.8(9) s | β$^+$ | $^{139}$Eu | 1/2+# | | |
| $^{139m}$Gd | 250(150)# keV | 250(150)# keV | 250(150)# keV | 4.8(9) s | β$^+$, p? | $^{138}$Sm | 1/2+# | | |
| $^{140}$Gd | 64 | 76 | 139.933674(30) | 15.8(4) s | β$^+$ (67(8)%) | $^{140}$Eu | 0+ | | |
| $^{140}$Gd | 64 | 76 | 139.933674(30) | 15.8(4) s | EC (33(8)%) | $^{140}$Eu | 0+ | | |
| $^{141}$Gd | 64 | 77 | 140.932126(21) | 14(4) s | β$^+$ (99.97%) | $^{141}$Eu | (1/2+) | | |
| $^{141}$Gd | 64 | 77 | 140.932126(21) | 14(4) s | β$^+$, p (0.03%) | $^{140}$Sm | (1/2+) | | |
| $^{141m}$Gd | 377.76(9) keV | 377.76(9) keV | 377.76(9) keV | 24.5(5) s | β$^+$ (89%) | $^{141}$Eu | (11/2−) | | |
| $^{141m}$Gd | 377.76(9) keV | 377.76(9) keV | 377.76(9) keV | 24.5(5) s | IT (11%) | $^{141}$Gd | (11/2−) | | |
| $^{142}$Gd | 64 | 78 | 141.928116(30) | 70.2(6) s | EC (52(5)%) | $^{142}$Eu | 0+ | | |
| $^{142}$Gd | 64 | 78 | 141.928116(30) | 70.2(6) s | β$^+$ (48(5)%) | $^{142}$Eu | 0+ | | |
| $^{143}$Gd | 64 | 79 | 142.92675(22) | 39(2) s | β$^+$ | $^{143}$Eu | 1/2+ | | |
| $^{143}$Gd | 64 | 79 | 142.92675(22) | 39(2) s | β$^+$, p? | $^{142}$Sm | 1/2+ | | |
| $^{143}$Gd | 64 | 79 | 142.92675(22) | 39(2) s | β$^+$, α? | $^{139}$Pm | 1/2+ | | |
| $^{143m}$Gd | 152.6(5) keV | 152.6(5) keV | 152.6(5) keV | 110.0(14) s | β$^+$ | $^{143}$Eu | 11/2− | | |
| $^{143m}$Gd | 152.6(5) keV | 152.6(5) keV | 152.6(5) keV | 110.0(14) s | β$^+$, p? | $^{142}$Sm | 11/2− | | |
| $^{143m}$Gd | 152.6(5) keV | 152.6(5) keV | 152.6(5) keV | 110.0(14) s | β$^+$, α? | $^{139}$Pm | 11/2− | | |
| $^{144}$Gd | 64 | 80 | 143.922963(30) | 4.47(6) min | β$^+$ | $^{144}$Eu | 0+ | | |
| $^{144m}$Gd | 3433.1(5) keV | 3433.1(5) keV | 3433.1(5) keV | 145(30) ns | IT | $^{144}$Gd | (10+) | | |
| $^{145}$Gd | 64 | 81 | 144.921710(21) | 23.0(4) min | β$^+$ | $^{145}$Eu | 1/2+ | | |
| $^{145m}$Gd | 749.1(2) keV | 749.1(2) keV | 749.1(2) keV | 85(3) s | IT (94.3%) | $^{145}$Gd | 11/2− | | |
| $^{145m}$Gd | 749.1(2) keV | 749.1(2) keV | 749.1(2) keV | 85(3) s | β$^+$ (5.7%) | $^{145}$Eu | 11/2− | | |
| $^{146}$Gd | 64 | 82 | 145.9183185(44) | 48.27(10) d | EC | $^{146}$Eu | 0+ | | |
| $^{147}$Gd | 64 | 83 | 146.9191010(20) | 38.06(12) h | β$^+$ | $^{147}$Eu | 7/2− | | |
| $^{147m}$Gd | 8587.8(5) keV | 8587.8(5) keV | 8587.8(5) keV | 510(20) ns | IT | $^{147}$Gd | 49/2+ | | |
| $^{148}$Gd | 64 | 84 | 147.9181214(16) | 86.9(39) y | α | $^{144}$Sm | 0+ | |
| $^{149}$Gd | 64 | 85 | 148.9193477(36) | 9.28(10) d | β$^+$ | $^{149}$Eu | 7/2− | | |
| $^{149}$Gd | 64 | 85 | 148.9193477(36) | 9.28(10) d | α (4.3×10$^{−4}$%) | $^{145}$Sm | 7/2− | | |
| $^{150}$Gd | 64 | 86 | 149.9186639(65) | 1.79(8)×10$^6$ y | α | $^{146}$Sm | 0+ | | |
| $^{151}$Gd | 64 | 87 | 150.9203549(32) | 123.9(10) d | EC | $^{151}$Eu | 7/2− | | |
| $^{151}$Gd | 64 | 87 | 150.9203549(32) | 123.9(10) d | α (1.1×10$^{−6}$%) | $^{147}$Sm | 7/2− | | |
| $^{152}$Gd | 64 | 88 | 151.9197984(11) | 1.08(8)×10$^{14}$ y | α | $^{148}$Sm | 0+ | 0.0020(1) | |
| $^{153}$Gd | 64 | 89 | 152.9217569(11) | 240.6(7) d | EC | $^{153}$Eu | 3/2− | | |
| $^{153m1}$Gd | 95.1737(8) keV | 95.1737(8) keV | 95.1737(8) keV | 3.5(4) μs | IT | $^{153}$Gd | 9/2+ | | |
| $^{153m2}$Gd | 171.188(4) keV | 171.188(4) keV | 171.188(4) keV | 76.0(14) μs | IT | $^{153}$Gd | (11/2−) | | |
| $^{154}$Gd | 64 | 90 | 153.9208730(11) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.0218(2) | |
| $^{155}$Gd | 64 | 91 | 154.9226294(11) | Observationally Stable | Observationally Stable | Observationally Stable | 3/2− | 0.1480(9) | |
| $^{155m}$Gd | 121.10(19) keV | 121.10(19) keV | 121.10(19) keV | 31.97(27) ms | IT | $^{155}$Gd | 11/2− | | |
| $^{156}$Gd | 64 | 92 | 155.9221301(11) | Stable | Stable | Stable | 0+ | 0.2047(3) | |
| $^{156m}$Gd | 2137.60(5) keV | 2137.60(5) keV | 2137.60(5) keV | 1.3(1) μs | IT | $^{156}$Gd | 7- | | |
| $^{157}$Gd | 64 | 93 | 156.9239674(10) | Stable | Stable | Stable | 3/2− | 0.1565(4) | |
| $^{157m1}$Gd | 63.916(5) keV | 63.916(5) keV | 63.916(5) keV | 460(40) ns | IT | $^{157}$Gd | 5/2+ | | |
| $^{157m2}$Gd | 426.539(23) keV | 426.539(23) keV | 426.539(23) keV | 18.5(23) μs | IT | $^{157}$Gd | 11/2− | | |
| $^{158}$Gd | 64 | 94 | 157.9241112(10) | Stable | Stable | Stable | 0+ | 0.2484(8) | |
| $^{159}$Gd | 64 | 95 | 158.9263958(11) | 18.479(4) h | β$^−$ | $^{159}$Tb | 3/2− | | |
| $^{160}$Gd | 64 | 96 | 159.9270612(12) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.2186(3) | |
| $^{161}$Gd | 64 | 97 | 160.9296763(16) | 3.646(3) min | β$^−$ | $^{161}$Tb | 5/2− | | |
| $^{162}$Gd | 64 | 98 | 161.9309918(43) | 8.4(2) min | β$^−$ | $^{162}$Tb | 0+ | | |
| $^{163}$Gd | 64 | 99 | 162.93409664(86) | 68(3) s | β$^−$ | $^{163}$Tb | 7/2+ | | |
| $^{163m}$Gd | 138.22(20) keV | 138.22(20) keV | 138.22(20) keV | 23.5(10) s | IT? | $^{163}$Gd | 1/2− | | |
| $^{163m}$Gd | 138.22(20) keV | 138.22(20) keV | 138.22(20) keV | 23.5(10) s | β$^−$ | $^{163}$Tb | 1/2− | | |
| $^{164}$Gd | 64 | 100 | 163.9359162(11) | 45(3) s | β$^−$ | $^{164}$Tb | 0+ | | |
| $^{164m}$Gd | 1095.8(4) keV | 1095.8(4) keV | 1095.8(4) keV | 589(18) ns | IT | $^{164}$Gd | (4−) | | |
| $^{165}$Gd | 64 | 101 | 164.9393171(14) | 11.6(10) s | β$^−$ | $^{165}$Tb | 1/2−# | | |
| $^{166}$Gd | 64 | 102 | 165.9416304(17) | 5.1(8) s | β$^−$ | $^{166}$Tb | 0+ | | |
| $^{166m}$Gd | 1601.5(11) keV | 1601.5(11) keV | 1601.5(11) keV | 950(60) ns | IT | $^{166}$Gd | (6−) | | |
| $^{167}$Gd | 64 | 103 | 166.9454900(56) | 4.2(3) s | β$^−$ | $^{167}$Tb | 5/2−# | | |
| $^{168}$Gd | 64 | 104 | 167.94831(32)# | 3.03(16) s | β$^−$ | $^{168}$Tb | 0+ | | |
| $^{169}$Gd | 64 | 105 | 168.95288(43)# | 750(210) ms | β$^−$ | $^{169}$Tb | 7/2−# | | |
| $^{169}$Gd | 64 | 105 | 168.95288(43)# | 750(210) ms | β$^−$, n? (<0.7%) | $^{168}$Tb | 7/2−# | | |
| $^{170}$Gd | 64 | 106 | 169.95615(54)# | 675+94 −75 ms | β$^−$ | $^{170}$Tb | 0+ | | |
| $^{170}$Gd | 64 | 106 | 169.95615(54)# | 675+94 −75 ms | β$^−$, n? (<3%) | $^{169}$Tb | 0+ | | |
| $^{171}$Gd | 64 | 107 | 170.96113(54)# | 392+145 −136 ms | β$^−$ | $^{171}$Tb | 9/2+# | | |
| $^{171}$Gd | 64 | 107 | 170.96113(54)# | 392+145 −136 ms | β$^−$, n? (<10%) | $^{170}$Tb | 9/2+# | | |
| $^{172}$Gd | 64 | 108 | 171.96461(32)# | 163+113 −99 ms | β$^−$ | $^{172}$Tb | 0+# | | |
| $^{172}$Gd | 64 | 108 | 171.96461(32)# | 163+113 −99 ms | β$^−$, n? (<50%) | $^{171}$Tb | 0+# | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Gd – 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
* ↑ 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.
* ↑ Order of ground state and isomer is uncertain.
* ↑ Theorized to also undergo β$^+$β$^+$ decay to $^{148}$Sm
* ↑ Theorized to also undergo β$^+$β$^+$ decay to $^{150}$Sm
* ↑ primordial radionuclide
* ↑ Theorized to also undergo β$^+$β$^+$ decay to $^{152}$Sm
* ↑ Believed to undergo α decay to $^{150}$Sm
* 1 2 3 4 5 6 Fission product
* ↑ Believed to undergo α decay to $^{151}$Sm
* ↑ Believed to undergo β$^−$β$^−$ decay to $^{160}$Dy with a half-life over 3.1×10$^{19}$ years

## Gadolinium-148

With a half-life of 86.9±3.9 year via alpha decay alone, gadolinium-148 would be ideal for radioisotope thermoelectric generators. However, gadolinium-148 cannot be economically synthesized in sufficient quantities to power a RTG.

## Gadolinium-153

Gadolinium-153 has a half-life of 240.4±10 d and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used as a gamma ray source for X-ray absorptiometry and fluorescence, for bone density gauges for osteoporosis screening, and for radiometric profiling in the Lixiscope portable x-ray imaging system, also known as the Lixi Profiler. In nuclear medicine, it serves to calibrate the equipment needed like single-photon emission computed tomography systems (SPECT) to make x-rays. It ensures that the machines work correctly to produce images of radioisotope distribution inside the patient. This isotope is produced in a nuclear reactor from europium or enriched gadolinium. It can also detect the loss of calcium in the hip and back bones, allowing the ability to diagnose osteoporosis.