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.

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.

Relative atomic mass: 157.25(3).

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	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)×106 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	64	88	151.9197910(27)	1.08(8)×1014 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			0+	0.0218(3)
155Gd	64	91	154.9226220(27)	Observationally Stable			3/2−	0.1480(12)
155mGd	121.05(19) keV			31.97(27) ms	IT	155Gd	11/2−
156Gd	64	92	155.9221227(27)	Stable			0+	0.2047(9)
156mGd	2137.60(5) keV			1.3(1) µs			7-
157Gd	64	93	156.9239601(27)	Stable			3/2−	0.1565(2)
158Gd	64	94	157.9241039(27)	Stable			0+	0.2484(7)
159Gd	64	95	158.9263887(27)	18.479(4) h	β−	159Tb	3/2−
160Gd	64	96	159.9270541(27)	Observationally Stable			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−#

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

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Isotopes of europium	Isotopes of gadolinium	Isotopes of terbium
Table of nuclides