Isotopes of gadolinium

Naturally occurring gadolinium (Gd) is composed of 6 stable isotopes, ¹⁵⁴Gd, ¹⁵⁵Gd, ¹⁵⁶Gd, ¹⁵⁷Gd, ¹⁵⁸Gd and ¹⁶⁰Gd, and 1 radioisotope, ¹⁵²Gd, with ¹⁵⁸Gd being the most abundant (24.84% natural abundance). The predicted double beta decay of ¹⁶⁰Gd has never been observed; only lower limit on its half-life of more than 1.3×10²¹ years has been set experimentally.^[1]

Thirty radioisotopes have been characterized, with the most stable being alpha-decaying ¹⁵²Gd (naturally occurring) with a half-life of 1.08×10¹⁴ years, and ¹⁵⁰Gd with a half-life of 1.79×10⁶ years. All of the remaining radioactive isotopes have half-lives less than 74.7 years. The majority of these have half-lives less than 24.6 seconds. Gadolinium isotopes have 10 metastable isomers, with the most stable being ^143mGd (t_1/2=110 seconds), ^145mGd (t_1/2=85 seconds) and ^141mGd (t_1/2=24.5 seconds).

The primary decay mode at atomic weights lower than the most abundant stable isotope, ¹⁵⁸Gd, is electron capture, and the primary mode at higher atomic weights is beta decay. The primary decay products for isotopes of weights lower than ¹⁵⁸Gd are the element Eu (europium) isotopes and the primary products at higher weights are the element Tb (terbium) isotopes.

Gadolinium-153 has a half-life of 240.4±10 days and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used as a gamma ray source in X-ray absorptiometry or bone density gauges for osteoporosis screening, and for radiometric profiling in the Lixiscope portable x-ray imaging system, also known as the Lixi Profiler.

Gadolinium-148 would be ideal for radioisotope thermoelectric generators due to its 74 year half life, high density, and dominant alpha decay mode. However, Gadolinium-148 cannot be economically synthesized in sufficient quantities to power a RTG.^[2]

Relative atomic mass: 157.25(3).

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life[n 1]	decay mode(s)[3][n 2]	daughter isotope(s)[n 3]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^134Gd	64	70	133.95537(43)#	0.4# s			0+
^135Gd	64	71	134.95257(54)#	1.1(2) s			3/2−
^136Gd	64	72	135.94734(43)#	1# s [>200 ns]	β^+	^136Eu
^137Gd	64	73	136.94502(43)#	2.2(2) s	β^+	^137Eu	7/2+#
					β^+, p (rare)	^136Sm
^138Gd	64	74	137.94012(21)#	4.7(9) s	β^+	^138Eu	0+
^138mGd	2232.7(11) keV			6(1) µs			(8−)
^139Gd	64	75	138.93824(21)#	5.7(3) s	β^+	^139Eu	9/2−#
					β^+, p (rare)	^138Sm
^139mGd	250(150)# keV			4.8(9) s			1/2+#
^140Gd	64	76	139.93367(3)	15.8(4) s	β^+	^140Eu	0+
^141Gd	64	77	140.932126(21)	14(4) s	β^+ (99.97%)	^141Eu	(1/2+)
					β^+, p (.03%)	^140Sm
^141mGd	377.8(2) keV			24.5(5) s	β^+ (89%)	^141Eu	(11/2−)
					IT (11%)	^141Gd
^142Gd	64	78	141.92812(3)	70.2(6) s	β^+	^142Eu	0+
^143Gd	64	79	142.92675(22)	39(2) s	β^+	^143Eu	(1/2)+
					β^+, α (rare)	^139Pm
					β^+, p (rare)	^142Sm
^143mGd	152.6(5) keV			110.0(14) s	β^+	^143Eu	(11/2−)
					β^+, α (rare)	^139Pm
					β^+, p (rare)	^142Sm
^144Gd	64	80	143.92296(3)	4.47(6) min	β^+	^144Eu	0+
^145Gd	64	81	144.921709(20)	23.0(4) min	β^+	^145Eu	1/2+
^145mGd	749.1(2) keV			85(3) s	IT (94.3%)	^145Gd	11/2−
					β^+ (5.7%)	^145Eu
^146Gd	64	82	145.918311(5)	48.27(10) d	EC	^146Eu	0+
^147Gd	64	83	146.919094(3)	38.06(12) h	β^+	^147Eu	7/2−
^147mGd	8587.8(4) keV			510(20) ns			(49/2+)
^148Gd	64	84	147.918115(3)	74.6(30) y	α	^144Sm	0+
					β^+β^+ (rare)	^148Sm
^149Gd	64	85	148.919341(4)	9.28(10) d	β^+	^149Eu	7/2−
					α (4.34×10^−4%)	^145Sm
^150Gd	64	86	149.918659(7)	1.79(8)×10^6 y	α	^146Sm	0+
					β^+β^+ (rare)	^150Sm
^151Gd	64	87	150.920348(4)	124(1) d	EC	^151Eu	7/2−
					α (10^−6%)	^147Sm
^152Gd[n 4]	64	88	151.9197910(27)	1.08(8)×10^14 y	α	^148Sm	0+	0.0020(1)
^153Gd	64	89	152.9217495(27)	240.4(10) d	EC	^153Eu	3/2−
^153m1Gd	95.1737(12) keV			3.5(4) µs			(9/2+)
^153m2Gd	171.189(5) keV			76.0(14) µs			(11/2−)
^154Gd	64	90	153.9208656(27)	Observationally Stable[n 5]			0+	0.0218(3)
^155Gd[n 6]	64	91	154.9226220(27)	Observationally Stable[n 7]			3/2−	0.1480(12)
^155mGd	121.05(19) keV			31.97(27) ms	IT	^155Gd	11/2−
^156Gd[n 6]	64	92	155.9221227(27)	Stable[n 8]			0+	0.2047(9)
^156mGd	2137.60(5) keV			1.3(1) µs			7-
^157Gd[n 6]	64	93	156.9239601(27)	Stable[n 8]			3/2−	0.1565(2)
^158Gd[n 6]	64	94	157.9241039(27)	Stable[n 8]			0+	0.2484(7)
^159Gd[n 6]	64	95	158.9263887(27)	18.479(4) h	β^−	^159Tb	3/2−
^160Gd[n 6]	64	96	159.9270541(27)	Observationally Stable[n 9]			0+	0.2186(19)
^161Gd	64	97	160.9296692(29)	3.646(3) min	β^−	^161Tb	5/2−
^162Gd	64	98	161.930985(5)	8.4(2) min	β^−	^162Tb	0+
^163Gd	64	99	162.93399(32)#	68(3) s	β^−	^163Tb	7/2+#
^164Gd	64	100	163.93586(43)#	45(3) s	β^−	^164Tb	0+
^165Gd	64	101	164.93938(54)#	10.3(16) s	β^−	^165Tb	1/2−#
^166Gd	64	102	165.94160(64)#	4.8(10) s	β^−	^166Tb	0+
^167Gd	64	103	166.94557(64)#	3# s	β^−	^167Tb	5/2−#
^168Gd	64	104	167.94836(75)#	300# ms	β^−	^168Tb	0+
^169Gd	64	105	168.95287(86)#	1# s	β^−	^169Tb	7/2−#

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 nearly-stable isotopes (half-life longer than the age of the universe)
4. primordial radionuclide
5. Believed to undergo α decay to ¹⁵⁰Sm
6. Fission product
7. Believed to undergo α decay to ¹⁵¹Sm
8. Theoretically capable of spontaneous fission
9. Believed to undergo β⁻β⁻ decay to ¹⁶⁰Dy with a half-life over 1.3×10²¹ years

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. F. A. Danevich; et al. (2001). "Quest for double beta decay of ¹⁶⁰Gd and Ce isotopes". Nuclear Physics A. 694: 375. arXiv:nucl-ex/0011020. Bibcode:2001NuPhA.694..375D. doi:10.1016/S0375-9474(01)00983-6.
2. "Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration". 2009. doi:10.17226/12653.
3. "Universal Nuclide Chart". nucleonica. Retrieved 2012-05-30. (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. Check date values in: |access-date= (help)
  • 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.