Naturally occurringgadolinium (₆₄Gd) is composed of 6 stableisotopes,¹⁵⁴Gd,¹⁵⁵Gd,¹⁵⁶Gd,¹⁵⁷Gd,¹⁵⁸Gd and¹⁶⁰Gd, and 1radioisotope,¹⁵²Gd, with¹⁵⁸Gd being the most abundant (24.84%natural abundance). The predicteddouble beta decay of¹⁶⁰Gd hasnever been observed; only a lower limit on itshalf-life of more than 1.3×10²¹ years has been set experimentally.^[5]

Thirty-three radioisotopes have been characterized, with the most stable being alpha-decaying¹⁵²Gd (naturally occurring) with a half-life of 1.08×10¹⁴ years, and¹⁵⁰Gd with a half-life of 1.79×10⁶ 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 metastableisomers, 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 primarydecay mode at atomic weights lower than the most abundant stable isotope,¹⁵⁸Gd, iselectron capture, and the primary mode at higher atomic weights isbeta decay. The primarydecay products for isotopes lighter than¹⁵⁸Gd areisotopes of europium and the primary products of heavier isotopes areisotopes of terbium.

With a half-life of86.9±3.9 year via alpha decay alone,^[2] gadolinium-148 would be ideal forradioisotope thermoelectric generators. However, gadolinium-148 cannot be economically synthesized in sufficient quantities to power a RTG.^[8]

Gadolinium-153 has a half-life of240.4±10 d and emits gamma radiation with strong peaks at 41keV and 102 keV. It is used as a gamma ray source forX-ray absorptiometry and fluorescence, for bone density gauges forosteoporosis screening, and for radiometric profiling in the Lixiscope portable x-ray imaging system, also known as the Lixi Profiler. Innuclear medicine, it serves to calibrate the equipment needed likesingle-photon emission computed tomography systems (SPECT) to makex-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 fromeuropium orenriched gadolinium.^[9] It can also detect the loss ofcalcium in the hip and back bones, allowing the ability to diagnose osteoporosis.^[10]

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",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:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003)."Atomic weights of the elements. Review 2000 (IUPAC Technical Report)".Pure and Applied Chemistry.75 (6):683–800.doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006)."Atomic weights of the elements 2005 (IUPAC Technical Report)".Pure and Applied Chemistry.78 (11):2051–2066.doi:10.1351/pac200678112051.
• "News & Notices: Standard Atomic Weights Revised".International Union of Pure and Applied Chemistry. 19 October 2005.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean;Wapstra, Aaldert Hendrik (2003),"The NUBASE evaluation of nuclear and decay properties",Nuclear Physics A,729:3–128,Bibcode:2003NuPhA.729....3A,doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center."NuDat 2.x database".Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.).CRC Handbook of Chemistry and Physics (85th ed.).Boca Raton, Florida:CRC Press.ISBN 978-0-8493-0485-9.

• Isotopes of gadolinium
• Gadolinium
• Lists of isotopes by element

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