Isotopes of europium

Naturally occurring europium (₆₃Eu) is composed of two isotopes, ¹⁵¹Eu and ¹⁵³Eu, with ¹⁵³Eu being the more abundant (52.2% natural abundance). While ¹⁵³Eu is observationally stable, ¹⁵¹Eu was found in 2007 to be unstable and undergo alpha decay;^[4]^[5] its measured half-life of 4.6 × 10¹⁸ years corresponds to 1 alpha decay per two minutes per kilogram of natural europium, so for practical purposes it can be considered stable. Besides the natural radioisotope ¹⁵¹Eu, artificial radioisotopes from ¹³⁰Eu to ¹⁷⁰Eu have been made, with the most stable being ¹⁵⁰Eu with a half-life of 36.9 years, ¹⁵²Eu with a half-life of 13.517 years, ¹⁵⁴Eu with a half-life of 8.592 years, and ¹⁵⁵Eu with a half-life of 4.742 years. All the others have half-lives shorter than 100 days, with the majority shorter than 3 minutes.

Quick facts Main isotopes, Decay ...

Isotopes of europium (₆₃Eu)

Main isotopes^[1]			Decay
Isotope	abundance	half-life (t_1/2)	mode	product
¹⁵⁰Eu	synth	36.9 y	β⁺	¹⁵⁰Sm
¹⁵¹Eu	47.8%	4.6×10¹⁸ y	α	¹⁴⁷Pm
¹⁵²Eu	synth	13.517 y	β⁺	¹⁵²Sm
¹⁵²Eu	synth	13.517 y	β⁻	¹⁵²Gd
¹⁵³Eu	52.2%	stable
¹⁵⁴Eu	synth	8.592 y	β⁻	¹⁵⁴Gd
¹⁵⁴Eu	synth	8.592 y	ε	¹⁵⁴Sm
¹⁵⁵Eu	synth	4.742 y	β⁻	¹⁵⁵Gd

Standard atomic weight A_r°(Eu)

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

Close

This element also has 27 metastable isomers, with the most stable being ^150mEu (12.8 hours), ^152m1Eu (9.3116 hours) and ^152m5Eu (96 minutes). The primary decay mode for isotopes lighter than ¹⁵³Eu is electron capture to samarium isotopes, and the primary mode for heavier isotopes is beta minus decay to gadolinium isotopes. ¹⁵²Eu and ¹⁵⁴Eu can decay either way, as can ^150mEu (meta state only).

List of isotopes

More information Nuclide, Z ...

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[6] ^{[n 2]}^{[n 3]}	Discovery year^[7]^[8]	Half-life^[1] ^{[n 4]}^{[n 5]}	Decay mode^[1] ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity^[1] ^{[n 9]}^{[n 5]}	Natural abundance (mole fraction)
Nuclide ^{[n 1]}	Excitation energy^{[n 5]}			Discovery year^[7]^[8]	Half-life^[1] ^{[n 4]}^{[n 5]}	Decay mode^[1] ^{[n 6]}	Daughter isotope ^{[n 7]}^{[n 8]}	Spin and parity^[1] ^{[n 9]}^{[n 5]}	Normal proportion^[1]	Range of variation
¹³⁰Eu	63	67	129.96402(58)#	2004	1.0(4) ms	p	¹²⁹Sm	(1+)
¹³¹Eu	63	68	130.95763(43)#	1998	17.8(19) ms	p (89%)	¹³⁰Sm	3/2+
						β⁺ (?%)	¹³¹Sm
						β⁺, p (?%)	¹³⁰Pm
¹³²Eu^[9]	63	69	131.95470(43)#	2026	100# ms [>310 ns]			1+#
¹³³Eu^[9]	63	70	132.94929(32)#	2026	200# ms [>310 ns]			5/2+#
¹³⁴Eu	63	71	133.94654(32)#	1989	0.5(2) s	β⁺	¹³⁴Sm
¹³⁴Eu	63	71	133.94654(32)#	1989	0.5(2) s	β⁺, p (?%)	¹³³Pm
¹³⁵Eu	63	72	134.94187(21)#	1989	1.5(2) s	β⁺	¹³⁵Sm	5/2+#
¹³⁶Eu	63	73	135.93962(21)#	1987	3.3(3) s	β⁺ (99.91%)	¹³⁶Sm	6+#
¹³⁶Eu	63	73	135.93962(21)#	1987	3.3(3) s	β⁺, p (0.09%)	¹³⁵Pm	6+#
^136mEu^{[n 10]}	100(100)# keV			1989	3.8(3) s	β⁺ (99.91%)	¹³⁶Sm	1+#
^136mEu^{[n 10]}	100(100)# keV			1989	3.8(3) s	β⁺, p (0.09%)	¹³⁵Pm	1+#
¹³⁷Eu	63	74	136.9354307(47)	1982	8.4(5) s	β⁺	¹³⁷Sm	5/2+#
¹³⁸Eu	63	75	137.933709(30)	1982	5# s			2−#
^138mEu^{[n 10]}	100(50)# keV			1999	12.1(6) s	β⁺	¹³⁸Sm	7−#
¹³⁹Eu	63	76	138.929792(14)	1975	17.9(6) s	β⁺	¹³⁹Sm	(11/2)−
^139mEu	148.3(3) keV			2011	10(2) μs	IT	¹³⁹Eu	(7/2+)
¹⁴⁰Eu	63	77	139.928088(55)	1982	1.51(2) s	β⁺ (95.1%)	¹⁴⁰Sm	1+
¹⁴⁰Eu	63	77	139.928088(55)	1982	1.51(2) s	EC (4.9%)	¹⁴⁰Sm	1+
^140m1Eu	210(14) keV			1991	125(2) ms	IT (>99%)	¹⁴⁰Eu	(5−)
^140m1Eu	210(14) keV			1991	125(2) ms	β⁺ (>1%)	¹⁴⁰Sm	(5−)
^140m2Eu	669(14) keV			2002	299.8(21) ns	IT	¹⁴⁰Eu	(8+)
¹⁴¹Eu	63	78	140.924932(14)	1977	40.7(7) s	β⁺	¹⁴¹Sm	5/2+
^141mEu	96.45(7) keV			1977	2.7(3) s	IT (86%)	¹⁴¹Eu	11/2−
^141mEu	96.45(7) keV			1977	2.7(3) s	β⁺ (14%)	¹⁴¹Sm	11/2−
¹⁴²Eu	63	79	141.923447(32)	1966	2.36(10) s	β⁺ (89.9%)	¹⁴²Sm	1+
¹⁴²Eu	63	79	141.923447(32)	1966	2.36(10) s	EC (11.1%)	¹⁴²Sm	1+
^142mEu	450(30) keV			1975	1.223(8) min	β⁺	¹⁴²Sm	8−
¹⁴³Eu	63	80	142.920299(12)	1965	2.59(2) min	β⁺	¹⁴³Sm	5/2+
^143mEu	389.51(4) keV			1976	50.0(5) μs	IT	¹⁴³Eu	11/2−
¹⁴⁴Eu	63	81	143.918819(12)	1965	10.2(1) s	β⁺	¹⁴⁴Sm	1+
^144mEu	1127.6(6) keV			1976	1.0(1) μs	IT	¹⁴⁴Eu	8−
¹⁴⁵Eu	63	82	144.9162727(33)	1951	5.93(4) d	β⁺	¹⁴⁵Sm	5/2+
^145mEu	716.0(3) keV			1975	490(30) ns	IT	¹⁴⁵Eu	11/2−
¹⁴⁶Eu	63	83	145.9172109(65)	1957	4.61(3) d	β⁺	¹⁴⁶Sm	4−
^146mEu	666.33(11) keV			1962	235(3) μs	IT	¹⁴⁶Eu	9+
¹⁴⁷Eu	63	84	146.9167524(28)	1951	24.1(6) d	β⁺	¹⁴⁷Sm	5/2+
¹⁴⁷Eu	63	84	146.9167524(28)	1951	24.1(6) d	α (0.0022%)	¹⁴³Pm	5/2+
^147mEu	625.27(5) keV			1960	765(15) ns	IT	¹⁴⁷Eu	11/2−
¹⁴⁸Eu	63	85	147.918091(11)	1951	54.5(5) d	β⁺	¹⁴⁸Sm	5−
¹⁴⁸Eu	63	85	147.918091(11)	1951	54.5(5) d	α (9.4×10⁻⁷%)	¹⁴⁴Pm	5−
^148mEu	720.4(3) keV			1980	162(8) ns	IT	¹⁴⁸Eu	9+
¹⁴⁹Eu	63	86	148.9179369(42)	1959	93.1(4) d	EC	¹⁴⁹Sm	5/2+
^149mEu	496.386(2) keV			1960	2.45(5) μs	IT	¹⁴⁹Eu	11/2−
¹⁵⁰Eu	63	87	149.9197071(67)	1950	36.9(9) y	β⁺	¹⁵⁰Sm	5−
^150mEu	41.7(10) keV			1961	12.8(1) h	β⁻ (89%)	¹⁵⁰Gd	0−
						β⁺ (11%)	¹⁵⁰Sm
						IT (<5×10⁻⁸%)^[10]	¹⁵⁰Eu
¹⁵¹Eu^{[n 11]}^{[n 12]}	63	88	150.9198566(13)	1933	4.6(12)×10¹⁸ y	α	¹⁴⁷Pm	5/2+	0.4781(6)
^151mEu	196.245(10) keV			1958	58.9(5) μs	IT	¹⁵¹Eu	11/2−
¹⁵²Eu	63	89	151.9217510(13)	1938	13.517(6) y	β⁺ (72.08%)	¹⁵²Sm	3−
¹⁵²Eu	63	89	151.9217510(13)	1938	13.517(6) y	β⁻ (27.92%)	¹⁵²Gd	3−
^152m1Eu	45.5998(4) keV			1947	9.3116(13) h	β⁻ (73%)	¹⁵²Gd	0−
^152m1Eu	45.5998(4) keV			1947	9.3116(13) h	β⁺ (27%)	¹⁵²Sm	0−
^152m2Eu	65.2969(4) keV			1978	940(80) ns	IT	¹⁵²Eu	1−
^152m3Eu	78.2331(4) keV			1978	165(10) ns	IT	¹⁵²Eu	1+
^152m4Eu	89.8496(4) keV			1965	384(10) ns	IT	¹⁵²Eu	4+
^152m5Eu	147.86(10) keV			1963	95.8(4) min	IT	¹⁵²Eu	8−
¹⁵³Eu^{[n 11]}	63	90	152.9212368(13)	1933	Observationally Stable^{[n 13]}^[11]^[12]			5/2+	0.5219(6)
^153mEu	1771.0(4) keV			2000	475(10) ns	IT	¹⁵³Eu	19/2−
¹⁵⁴Eu^{[n 11]}	63	91	153.9229857(13)	1947	8.592(3) y	β⁻ (99.98%)	¹⁵⁴Gd	3−
¹⁵⁴Eu^{[n 11]}	63	91	153.9229857(13)	1947	8.592(3) y	EC (0.02%)	¹⁵⁴Sm	3−
^154m1Eu	68.1702(4) keV			1965	2.2(1) μs	IT	¹⁵⁴Eu	2+
^154m2Eu	145.3(3) keV			1975	46.3(4) min	IT	¹⁵⁴Eu	(8−)
¹⁵⁵Eu^{[n 11]}	63	92	154.9228998(13)	1951	4.742(8) y	β⁻	¹⁵⁵Gd	5/2+
¹⁵⁶Eu^{[n 11]}	63	93	155.9247630(38)	1951	15.19(8) d	β⁻	¹⁵⁶Gd	0+
¹⁵⁷Eu	63	94	156.9254326(45)	1951	15.18(3) h	β⁻	¹⁵⁷Gd	5/2+
¹⁵⁸Eu	63	95	157.9277822(22)	1951	45.9(2) min	β⁻	¹⁵⁸Gd	1−
¹⁵⁹Eu	63	96	158.9290995(46)	1961	18.1(1) min	β⁻	¹⁵⁹Gd	5/2+
¹⁶⁰Eu	63	97	159.93183698(97)	1973	42.6(5) s	β⁻	¹⁶⁰Gd	(5−)
^160mEu	93.0(12) keV			2018	30.8(5) s	IT	¹⁶⁰Eu	(1−)
¹⁶¹Eu	63	98	160.933664(11)	1986	26.2(23) s	β⁻	¹⁶¹Gd	5/2+#
¹⁶²Eu	63	99	161.9369583(14)	1987	~10 s	β⁻	¹⁶²Gd	1+#
^162mEu	158.0(17) keV			2018	15.0(5) s	IT	¹⁶²Eu	(6+)
¹⁶³Eu	63	100	162.93926551(97)	2007	7.7(4) s	β⁻	¹⁶³Gd	5/2+#
^163mEu	964.5(5) keV			2017	911(24) ns	IT	¹⁶³Eu	(13/2−)
¹⁶⁴Eu	63	101	163.9428529(22)	2007	4.16(19) s	β⁻	¹⁶⁴Gd	3−#
¹⁶⁵Eu	63	102	164.9455401(56)	2007	2.163+0.139 −0.120 s^[13]	β⁻	¹⁶⁵Gd	5/2+#
¹⁶⁶Eu	63	103	165.94981(11)#	2012	1.277+0.100 −0.145 s^[13]	β⁻ (99.37%)	¹⁶⁶Gd	0−#
¹⁶⁶Eu	63	103	165.94981(11)#	2012	1.277+0.100 −0.145 s^[13]	β⁻, n (0.63%)	¹⁶⁵Gd	0−#
¹⁶⁷Eu	63	104	166.95301(43)#	2012	852+76 −54 ms^[13]	β⁻ (98.05%)	¹⁶⁷Gd	5/2+#
¹⁶⁷Eu	63	104	166.95301(43)#	2012	852+76 −54 ms^[13]	β⁻, n (1.95%)	¹⁶⁶Gd	5/2+#
¹⁶⁸Eu	63	105	167.95786(43)#	2012	440+48 −47 ms^[13]	β⁻ (96.05%)	¹⁶⁸Gd	6−#
¹⁶⁸Eu	63	105	167.95786(43)#	2012	440+48 −47 ms^[13]	β⁻, n (3.95%)	¹⁶⁷Gd	6−#
¹⁶⁹Eu	63	106	168.96172(54)#	2018	389+92 −88 ms^[13]	β⁻ (85.38%)	¹⁶⁹Gd	5/2+#
¹⁶⁹Eu	63	106	168.96172(54)#	2018	389+92 −88 ms^[13]	β⁻, n (14.62%)	¹⁶⁸Gd	5/2+#
¹⁷⁰Eu	63	107	169.96687(54)#	2022	197+74 −71 ms^[13]	β⁻ (>76%)	¹⁷⁰Gd
¹⁷⁰Eu	63	107	169.96687(54)#	2022	197+74 −71 ms^[13]	β⁻, n (<24%)	¹⁶⁹Gd
This table header & footer: view

Close

[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:

α: Alpha decay

β⁺: Positron emission

EC: Electron capture

β⁻: Beta decay

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]
Order of ground state and isomer is uncertain.
[11]
Fission product
[12]
Primordial radionuclide
[13]
Believed to undergo α decay to ¹⁴⁹Pm with a half-life over 5.5×10¹⁷ years

Europium-155

More information Nuclide, t1⁄2 ...

Medium-lived fission products
v
t
e
Nuclide	t_1⁄2	Yield	Q^{[a 1]}	βγ
	(a)	(%)^{[a 2]}	(keV)
¹⁵⁵Eu	4.74	0.0803^{[a 3]}	252	βγ
⁸⁵Kr	10.73	0.2180^{[a 4]}	687	βγ
^113mCd	13.9	0.0008^{[a 3]}	316	β
⁹⁰Sr	28.91	4.505	2826^{[a 5]}	β
¹³⁷Cs	30.04	6.337	1176	βγ
^121mSn	43.9	0.00005	390	βγ
¹⁵¹Sm	94.6	0.5314^{[a 3]}	77	β
[1] Decay energy is split among β, neutrino, and γ if any. [2] Per 65 thermal neutron fissions of ²³⁵U and 35 of ²³⁹Pu. [3] Neutron poison; in thermal reactors, most is destroyed by further neutron capture. [4] Less than 1/4 of mass-85 fission products as most bypass ground state: ⁸⁵Br → ^85mKr → ⁸⁵Rb. [5] Has decay energy 546 keV; its decay product ⁹⁰Y has decay energy 2.28 MeV with weak gamma branching.

Close

Europium-155 is a fission product with a half-life of 4.742 years and has a maximum decay energy of 252 keV. Because of its position on the high-mass end of the yield curve, it has a low fission product yield, about 1 to 2% that of the most abundant fission products.

¹⁵⁵Eu's large neutron capture cross section means that most of 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 captures on ¹⁵³Eu and ¹⁵⁴Eu, whose direct fission yield is extremely small as its mass chain stops at ¹⁵⁴Sm. However, the high cross sections, and even higher for 155 than 154, mean that both ¹⁵⁵Eu and ¹⁵⁴Eu are destroyed faster than they are produced. See the table below for numeric details on this process.

More information Isotope, Half-life ...

Isotope	Half-life	Relative yield (fission)	Thermal neutron	Resonance integral
Eu-153	Stable	5	350	1500
Eu-154	8.592 years	~0	1500	1600
Eu-155	4.742 years	1	3900	16000

Close

Isotopes of europium

List of isotopes

Europium-155

See also

References

Related Articles

α:	Alpha decay
β⁺:	Positron emission
EC:	Electron capture
β⁻:	Beta decay
IT:	Isomeric transition
p:	Proton emission