Isotopes of europium

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, 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).

Isotopes of europium (₆₃Eu)

Main isotopes^[1] Decay abun­dance half-life (t1/2) mode pro­duct ^150Eu synth 36.9 y ε ^150Sm ^151Eu 47.8% 5×10^18 y α ^147Pm ^152Eu synth 13.54 y ε ^152Sm β^− ^152Gd ^153Eu 52.2% stable ^154Eu synth 8.59 y β^− ^154Gd ^155Eu synth 4.76 y β^− ^155Gd
Standard atomic weight Ar°(Eu)
	151.964±0.001 151.96±0.01 (abridged)^[2]^[3]
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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)
	Excitation energy^[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
					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
					β^+, p (rare)	^133Pm
^135Eu	63	72	134.94182(32)#	1.5(2) s	β^+	^135Sm	11/2−#
					β^+, p	^134Pm
^136Eu	63	73	135.93960(21)#	3.3(3) s	β^+ (99.91%)	^136Sm	(7+)
					β^+, p (.09%)	^135Pm
^136mEu	0(500)# keV			3.8(3) s	β^+ (99.91%)	^136Sm	(3+)
					β^+, p (.09%)	^135Pm
^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^+	^140Sm	1+
^140mEu	210(15) keV			125(2) ms	IT (99%)	^140Eu	5−#
					β^+(1%)	^140Sm
^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−
					β^+ (14%)	^141Sm
^142Eu	63	79	141.92343(3)	2.36(10) s	β^+	^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+
					α (.0022%)	^143Pm
^148Eu	63	85	147.918086(11)	54.5(5) d	β^+ (100%)	^148Sm	5−
					α (9.39×10^−7%)	^144Pm
^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)	4.62×10^18 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%), β^+ (0.027%)	^152Sm	3−
					β^− (27.9%)	^152Gd
^152m1Eu	45.5998(4) keV			9.3116(13) h	β^− (72%)	^152Gd	0−
					β^+ (28%)	^152Sm
^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−
					EC (.02%)	^154Sm
^154m1Eu	145.3(3) keV			46.3(4) min	IT	^154Eu	(8−)
^154m2Eu	68.1702(4) keV			2.2(1) µs			2+
^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
					β^−, n (0.63%)	^165Gd
^167Eu	63	104	166.95321(86)#	852+76 −54 s^[7]	β^− (98.05%)	^167Gd	5/2+#
					β^−, n (1.95%)	^166Gd
^168Eu	63	105		440+48 −47 s^[7]	β^− (96.05%)	^168Gd
					β^−, n (3.95%)	^167Gd
^169Eu	63	106		389+92 −88 s^[7]	β^− (85.38%)	^169Gd
					β^−, n (14.62%)	^168Gd
^170Eu	63	107		197+74 −71 s^[7]	β^−	^170Gd
					β^−, n	^169Gd
This table header & footer: view

1. ^mEu – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   p:	Proton emission

7. Bold italics symbol as daughter – Daughter product is nearly stable.
8. Bold symbol as daughter – Daughter product is stable.
9. ( ) spin value – Indicates spin with weak assignment arguments.
10. primordial radionuclide
11. Fission product
12. 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]}

	t½ (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

1. 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.
2. "Standard Atomic Weights: Europium". CIAAW. 1995.
3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (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.
4. 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.
5. 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.
6. 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.
7. 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.
8. (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.