Isotopes of gadolinium

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Naturally occurring gadolinium (Gd) is composed of 5 stable isotopes, ¹⁵⁴Gd, ¹⁵⁵Gd, ¹⁵⁶Gd, ¹⁵⁷Gd and ¹⁵⁸Gd, and 2 radioisotopes, ¹⁵²Gd and ¹⁶⁰Gd, with ¹⁵⁸Gd being the most abundant (24.84% natural abundance).

Thirty radioisotopes have been characterized, with the most stable being ¹⁶⁰Gd with a half-life of more than 1.3×10²¹ years (the decay has not been observed—only the lower limit on the half-life is known), alpha-decaying ¹⁵²Gd with a half-life of 1.08×10¹⁴ years, and ¹⁵⁰Gd with a half-life of 1.79×10⁶ years. All of the remaining isotopes are radioactive, having half-lives less than 74.7 years. The majority of these have half-lives less than 24.6 seconds. Gadolinium isotopes have 4 metastable isomers, with the most stable being ^143mGd (t_½ 110 seconds), ^145mGd (t_½ 85 seconds) and ^141mGd (t_½ 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 41keV and 102keV. It is used as a gamma ray source in x-ray absorptiometry or bone density gauges for osteoporosis screening, and in the Lixiscope portable x-ray imaging system.
Standard atomic mass: 157.25(3) u

[edit] Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
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]
¹³⁷Gd	64	73	136.94502(43)#	2.2(2) s	7/2+#
¹³⁸Gd	64	74	137.94012(21)#	4.7(9) s	0+
^138mGd	2232.7(11) keV			6(1) µs	(8-)
¹³⁹Gd	64	75	138.93824(21)#	5.7(3) s	9/2-#
^139mGd	250(150)# keV			4.8(9) s	1/2+#
¹⁴⁰Gd	64	76	139.93367(3)	15.8(4) s	0+
¹⁴¹Gd	64	77	140.932126(21)	14(4) s	(1/2+)
^141mGd	377.8(2) keV			24.5(5) s	(11/2-)
¹⁴²Gd	64	78	141.92812(3)	70.2(6) s	0+
¹⁴³Gd	64	79	142.92675(22)	39(2) s	(1/2)+
^143mGd	152.6(5) keV			110.0(14) s	(11/2-)
¹⁴⁴Gd	64	80	143.92296(3)	4.47(6) min	0+
¹⁴⁵Gd	64	81	144.921709(20)	23.0(4) min	1/2+
^145mGd	749.1(2) keV			85(3) s	11/2-
¹⁴⁶Gd	64	82	145.918311(5)	48.27(10) d	0+
¹⁴⁷Gd	64	83	146.919094(3)	38.06(12) h	7/2-
^147mGd	8587.8(4) keV			510(20) ns	(49/2+)
¹⁴⁸Gd	64	84	147.918115(3)	74.6(30) a	0+
¹⁴⁹Gd	64	85	148.919341(4)	9.28(10) d	7/2-
¹⁵⁰Gd	64	86	149.918659(7)	1.79(8)E+6 a	0+
¹⁵¹Gd	64	87	150.920348(4)	124(1) d	7/2-
¹⁵²Gd	64	88	151.9197910(27)	1.08(8)E+14 a	0+	0.0020(1)
¹⁵³Gd	64	89	152.9217495(27)	240.4(10) d	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)	STABLE	0+	0.0218(3)
¹⁵⁵Gd	64	91	154.9226220(27)	STABLE	3/2-	0.1480(12)
^155mGd	121.05(19) keV			31.97(27) ms	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	3/2-
¹⁶⁰Gd	64	96	159.9270541(27)	STABLE [>31E+18 a]	0+	0.2186(19)
¹⁶¹Gd	64	97	160.9296692(29)	3.646(3) min	5/2-
¹⁶²Gd	64	98	161.930985(5)	8.4(2) min	0+
¹⁶³Gd	64	99	162.93399(32)#	68(3) s	7/2+#
¹⁶⁴Gd	64	100	163.93586(43)#	45(3) s	0+
¹⁶⁵Gd	64	101	164.93938(54)#	10.3(16) s	1/2-#
¹⁶⁶Gd	64	102	165.94160(64)#	4.8(10) s	0+
¹⁶⁷Gd	64	103	166.94557(64)#	3# s	5/2-#
¹⁶⁸Gd	64	104	167.94836(75)#	300# ms	0+
¹⁶⁹Gd	64	105	168.95287(86)#	1# s	7/2-#

[edit] 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.

[edit] References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.