Isotopes of europium (₆₃Eu)

Main isotopes^[1]			Decay
	abundance	half-life (t_1/2)	mode	product
¹⁵⁰Eu	synth	36.9 y	β⁺	¹⁵⁰Sm
¹⁵¹Eu	47.8%	4.62×10¹⁸ y	α	¹⁴⁷Pm
¹⁵²Eu	synth	13.54 y	ε	¹⁵²Sm
¹⁵²Eu	synth	13.54 y	β⁻	¹⁵²Gd
¹⁵³Eu	52.2%	stable
¹⁵⁴Eu	synth	8.59 y	β⁻	¹⁵⁴Gd
¹⁵⁵Eu	synth	4.76 y	β⁻	¹⁵⁵Gd

Standard atomic weight A_r°(Eu)

151.964±0.001^[2]
151.96±0.01 (abridged)^[3]

Naturally occurring europium (₆₃Eu) is composed of two isotopes, ¹⁵¹Eu and ¹⁵³Eu, with ¹⁵³Eu being the most abundant (52.2% natural abundance). While ¹⁵³Eu is observationally stable (theoretically can undergo alpha decay with half-life over 5.5×10¹⁷ years), ¹⁵¹Eu was found in 2007 to be unstable and undergo alpha decay.^[4] The half-life is measured to be (4.62 ± 0.95(stat.) ± 0.68(syst.)) × 10¹⁸ years^[5] which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium. Besides the natural radioisotope ¹⁵¹Eu, 36 artificial radioisotopes have been characterized, with the most stable being ¹⁵⁰Eu with a half-life of 36.9 years, ¹⁵²Eu with a half-life of 13.516 years, ¹⁵⁴Eu with a half-life of 8.593 years, and ¹⁵⁵Eu with a half-life of 4.7612 years. The majority of the remaining radioactive isotopes, which range from ¹³⁰Eu to ¹⁷⁰Eu, have half-lives that are less than 12.2 seconds. This element also has 18 meta states, with the most stable being ^150mEu (t_1/2 12.8 hours), ^152m1Eu (t_1/2 9.3116 hours) and ^152m2Eu (t_1/2 96 minutes).

The primary decay mode before the most abundant stable isotope, ¹⁵³Eu, is electron capture, and the primary mode after is beta decay. The primary decay products before ¹⁵³Eu are isotopes of samarium and the primary products after are isotopes of gadolinium.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da) ^{[n 2]}^{[n 3]}	Half-life ^{[n 4]}^{[n 5]}	Decay mode ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity ^{[n 9]}^{[n 5]}	Natural abundance (mole fraction)
Nuclide ^{[n 1]}	Excitation energy^{[n 5]}			Half-life ^{[n 4]}^{[n 5]}	Decay mode ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity ^{[n 9]}^{[n 5]}	Normal proportion	Range of variation
¹³⁰Eu	63	67	129.96357(54)#	1.1(5) ms [0.9(+5−3) ms]			2+#
¹³¹Eu	63	68	130.95775(43)#	17.8(19) ms			3/2+
¹³²Eu	63	69	131.95437(43)#	100# ms	β⁺	¹³²Sm
¹³²Eu	63	69	131.95437(43)#	100# ms	p	¹³¹Sm
¹³³Eu	63	70	132.94924(32)#	200# ms	β⁺	¹³³Sm	11/2−#
¹³⁴Eu	63	71	133.94651(21)#	0.5(2) s	β⁺	¹³⁴Sm
¹³⁴Eu	63	71	133.94651(21)#	0.5(2) s	β⁺, p (rare)	¹³³Pm
¹³⁵Eu	63	72	134.94182(32)#	1.5(2) s	β⁺	¹³⁵Sm	11/2−#
¹³⁵Eu	63	72	134.94182(32)#	1.5(2) s	β⁺, p	¹³⁴Pm	11/2−#
¹³⁶Eu	63	73	135.93960(21)#	3.3(3) s	β⁺ (99.91%)	¹³⁶Sm	(7+)
¹³⁶Eu	63	73	135.93960(21)#	3.3(3) s	β⁺, p (.09%)	¹³⁵Pm	(7+)
^136mEu	0(500)# keV			3.8(3) s	β⁺ (99.91%)	¹³⁶Sm	(3+)
^136mEu	0(500)# keV			3.8(3) s	β⁺, p (.09%)	¹³⁵Pm	(3+)
¹³⁷Eu	63	74	136.93557(21)#	8.4(5) s	β⁺	¹³⁷Sm	11/2−#
¹³⁸Eu	63	75	137.93371(3)	12.1(6) s	β⁺	¹³⁸Sm	(6−)
¹³⁹Eu	63	76	138.929792(14)	17.9(6) s	β⁺	¹³⁹Sm	(11/2)−
¹⁴⁰Eu	63	77	139.92809(6)	1.51(2) s	β⁺ (95.1(7)%)	¹⁴⁰Sm	1+
¹⁴⁰Eu	63	77	139.92809(6)	1.51(2) s	EC (4.9(7)%)	¹⁴⁰Sm	1+
^140mEu	210(15) keV			125(2) ms	IT (99%)	¹⁴⁰Eu	5−#
^140mEu	210(15) keV			125(2) ms	β⁺(1%)	¹⁴⁰Sm	5−#
¹⁴¹Eu	63	78	140.924931(14)	40.7(7) s	β⁺	¹⁴¹Sm	5/2+
^141mEu	96.45(7) keV			2.7(3) s	IT (86%)	¹⁴¹Eu	11/2−
^141mEu	96.45(7) keV			2.7(3) s	β⁺ (14%)	¹⁴¹Sm	11/2−
¹⁴²Eu	63	79	141.92343(3)	2.36(10) s	β⁺ (89.9(16)%)	¹⁴²Sm	1+
¹⁴²Eu	63	79	141.92343(3)	2.36(10) s	EC (11.1(16)%)	¹⁴²Sm	1+
^142mEu	460(30) keV			1.223(8) min	β⁺	¹⁴²Sm	8−
¹⁴³Eu	63	80	142.920298(12)	2.59(2) min	β⁺	¹⁴³Sm	5/2+
^143mEu	389.51(4) keV			50.0(5) µs			11/2−
¹⁴⁴Eu	63	81	143.918817(12)	10.2(1) s	β⁺	¹⁴⁴Sm	1+
^144mEu	1127.6(6) keV			1.0(1) µs			(8−)
¹⁴⁵Eu	63	82	144.916265(4)	5.93(4) d	β⁺	¹⁴⁵Sm	5/2+
^145mEu	716.0(3) keV			490 ns			11/2−
¹⁴⁶Eu	63	83	145.917206(7)	4.61(3) d	β⁺	¹⁴⁶Sm	4−
^146mEu	666.37(16) keV			235(3) µs			9+
¹⁴⁷Eu	63	84	146.916746(3)	24.1(6) d	β⁺ (99.99%)	¹⁴⁷Sm	5/2+
¹⁴⁷Eu	63	84	146.916746(3)	24.1(6) d	α (.0022%)	¹⁴³Pm	5/2+
¹⁴⁸Eu	63	85	147.918086(11)	54.5(5) d	β⁺ (100%)	¹⁴⁸Sm	5−
¹⁴⁸Eu	63	85	147.918086(11)	54.5(5) d	α (9.39×10⁻⁷%)	¹⁴⁴Pm	5−
¹⁴⁹Eu	63	86	148.917931(5)	93.1(4) d	EC	¹⁴⁹Sm	5/2+
¹⁵⁰Eu	63	87	149.919702(7)	36.9(9) y	β⁺	¹⁵⁰Sm	5(−)
^150mEu	42.1(5) keV			12.8(1) h	β⁻ (89%)	¹⁵⁰Gd	0−
					β⁺ (11%)	¹⁵⁰Sm
					IT (5×10⁻⁸%)	¹⁵⁰Eu
¹⁵¹Eu^{[n 10]}	63	88	150.9198502(26)	4.62×10¹⁸ y	α	¹⁴⁷Pm	5/2+	0.4781(6)
^151mEu	196.245(10) keV			58.9(5) µs			11/2−
¹⁵²Eu	63	89	151.9217445(26)	13.537(6) y	EC (72.09%)	¹⁵²Sm	3−
					β⁻ (27.9%)	¹⁵²Gd
					β⁺ (0.027%)	¹⁵²Sm
^152m1Eu	45.5998(4) keV			9.3116(13) h	β⁻ (72%)	¹⁵²Gd	0−
^152m1Eu	45.5998(4) keV			9.3116(13) h	β⁺ (28%)	¹⁵²Sm	0−
^152m2Eu	65.2969(4) keV			0.94(8) µs			1−
^152m3Eu	78.2331(4) keV			165(10) ns			1+
^152m4Eu	89.8496(4) keV			384(10) ns			4+
^152m5Eu	147.86(10) keV			96(1) min			8−
¹⁵³Eu^{[n 11]}	63	90	152.9212303(26)	Observationally Stable^{[n 12]}^[6]			5/2+	0.5219(6)
¹⁵⁴Eu^{[n 11]}	63	91	153.9229792(26)	8.593(4) y	β⁻ (99.98%)	¹⁵⁴Gd	3−
¹⁵⁴Eu^{[n 11]}	63	91	153.9229792(26)	8.593(4) y	EC (.02%)	¹⁵⁴Sm	3−
^154m1Eu	68.1702(4) keV			2.2(1) µs	IT	¹⁵⁴Eu	2+
^154m2Eu	145.3(3) keV			46.3(4) min	IT	¹⁵⁴Eu	(8−)
¹⁵⁵Eu^{[n 11]}	63	92	154.9228933(27)	4.7611(13) y	β⁻	¹⁵⁵Gd	5/2+
¹⁵⁶Eu^{[n 11]}	63	93	155.924752(6)	15.19(8) d	β⁻	¹⁵⁶Gd	0+
¹⁵⁷Eu	63	94	156.925424(6)	15.18(3) h	β⁻	¹⁵⁷Gd	5/2+
¹⁵⁸Eu	63	95	157.92785(8)	45.9(2) min	β⁻	¹⁵⁸Gd	(1−)
¹⁵⁹Eu	63	96	158.929089(8)	18.1(1) min	β⁻	¹⁵⁹Gd	5/2+
¹⁶⁰Eu	63	97	159.93197(22)#	38(4) s	β⁻	¹⁶⁰Gd	1(−)
¹⁶¹Eu	63	98	160.93368(32)#	26(3) s	β⁻	¹⁶¹Gd	5/2+#
¹⁶²Eu	63	99	161.93704(32)#	10.6(10) s	β⁻	¹⁶²Gd
¹⁶³Eu	63	100	162.93921(54)#	7.7(4) s	β⁻	¹⁶³Gd	5/2+#
^163mEu	964.5(10) keV			911(24) ns			(13/2−)
¹⁶⁴Eu	63	101	163.94299(64)#	4.16(19) s	β⁻	¹⁶⁴Gd
¹⁶⁵Eu	63	102	164.94572(75)#	2.163+0.139 −0.120 s^[7]	β⁻	¹⁶⁵Gd	5/2+#
¹⁶⁶Eu	63	103	165.94997(86)#	1.277+0.100 −0.145 s^[7]	β⁻ (99.37%)	¹⁶⁶Gd
¹⁶⁶Eu	63	103	165.94997(86)#	1.277+0.100 −0.145 s^[7]	β⁻, n (0.63%)	¹⁶⁵Gd
¹⁶⁷Eu	63	104	166.95321(86)#	852+76 −54 s^[7]	β⁻ (98.05%)	¹⁶⁷Gd	5/2+#
¹⁶⁷Eu	63	104	166.95321(86)#	852+76 −54 s^[7]	β⁻, n (1.95%)	¹⁶⁶Gd	5/2+#
¹⁶⁸Eu	63	105		440+48 −47 s^[7]	β⁻ (96.05%)	¹⁶⁸Gd
¹⁶⁸Eu	63	105		440+48 −47 s^[7]	β⁻, n (3.95%)	¹⁶⁷Gd
¹⁶⁹Eu	63	106		389+92 −88 s^[7]	β⁻ (85.38%)	¹⁶⁹Gd
¹⁶⁹Eu	63	106		389+92 −88 s^[7]	β⁻, n (14.62%)	¹⁶⁸Gd
¹⁷⁰Eu	63	107		197+74 −71 s^[7]	β⁻	¹⁷⁰Gd
¹⁷⁰Eu	63	107		197+74 −71 s^[7]	β⁻, n	¹⁶⁹Gd
This table header & footer: view

^ ^mEu – 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.
^ ^a ^b ^c # – 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

p: Proton emission
^ 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.
^ primordial radionuclide
^ ^a ^b ^c ^d Fission product
^ Believed to undergo α decay to ¹⁴⁹Pm with a half-life over 5.5×10¹⁷ years

Europium-155

Medium-lived
fission products ^{[further explanation needed]}
	t_½ (year)	Yield (%)	Q (keV)	βγ
¹⁵⁵Eu	4.76	0.0803	252	βγ
⁸⁵Kr	10.76	0.2180	687	βγ
^113mCd	14.1	0.0008	316	β
⁹⁰Sr	28.9	4.505	2826	β
¹³⁷Cs	30.23	6.337	1176	βγ
^121mSn	43.9	0.00005	390	βγ
¹⁵¹Sm	88.8	0.5314	77	β

Europium-155 is a fission product with a half-life of 4.76 years. It has a maximum decay energy of 252 keV. In a thermal reactor (almost all current nuclear power plants), it has a low fission product yield, about half of one percent as much as the most abundant fission products.

¹⁵⁵Eu's large neutron capture cross section (about 3900 barns for thermal neutrons, 16000 resonance integral) means that most of even the small amount produced is destroyed in the course of the nuclear fuel's burnup. Yield, decay energy, and half-life are all far less than that of ¹³⁷Cs and ⁹⁰Sr, so ¹⁵⁵Eu is not a significant contributor to nuclear waste.

Some ¹⁵⁵Eu is also produced by successive neutron capture on ¹⁵³Eu (nonradioactive, 350 barns thermal, 1500 resonance integral, yield is about 5 times as great as ¹⁵⁵Eu) and ¹⁵⁴Eu (half-life 8.6 years, 1400 barns thermal, 1600 resonance integral, fission yield is extremely small because beta decay stops at ¹⁵⁴Sm). However, the differing cross sections mean that both ¹⁵⁵Eu and ¹⁵⁴Eu are destroyed faster than they are produced.

¹⁵⁴Eu is a prolific emitter of gamma radiation.^[8]

Isotope	Half-life	Relative yield	Thermal neutron	Resonance integral
Eu-153	Stable	5	350	1500
Eu-154	8.6 years	Nearly 0	1500	1600
Eu-155	4.76 years	1	3900	16000

References

^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ "Standard Atomic Weights: Europium". CIAAW. 1995.
^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ Belli, P.; et al. (2007). "Search for α decay of natural europium". Nuclear Physics A. 789 (1–4): 15–29. Bibcode:2007NuPhA.789...15B. doi:10.1016/j.nuclphysa.2007.03.001.
^ Casali, N.; Nagorny, S. S.; Orio, F.; Pattavina, L.; et al. (2014). "Discovery of the ¹⁵¹Eu α decay". Journal of Physics G: Nuclear and Particle Physics. 41 (7): 075101. arXiv:1311.2834. Bibcode:2014JPhG...41g5101C. doi:10.1088/0954-3899/41/7/075101. S2CID 116920467.
^ Danevich, F. A.; Andreotti, E.; Hult, M.; Marissens, G.; Tretyak, V. I.; Yuksel, A. (2012). "Search for α decay of ¹⁵¹Eu to the first excited level of ¹⁴⁷Pm using underground γ-ray spectrometry". European Physical Journal A. 48 (157): 157. arXiv:1301.3465. Bibcode:2012EPJA...48..157D. doi:10.1140/epja/i2012-12157-7. S2CID 118657922.
^ ^a ^b ^c ^d ^e ^f Kiss, G. G.; Vitéz-Sveiczer, A.; Saito, Y.; et al. (2022). "Measuring the β-decay properties of neutron-rich exotic Pm, Sm, Eu, and Gd isotopes to constrain the nucleosynthesis yields in the rare-earth region". The Astrophysical Journal. 936 (107): 107. Bibcode:2022ApJ...936..107K. doi:10.3847/1538-4357/ac80fc. hdl:2117/375253.
^ "Archived copy" (PDF). Archived from the original (PDF) on 2011-07-06. Retrieved 2011-04-02.((cite web)): CS1 maint: archived copy as title (link)

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.