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Isotopes of europium

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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; 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.

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

Europium-132

|-id=Europium-130 | 130Eu | 129.96402(58)# | 1.0(4) ms | p | 129Sm | (1+) | | |-id=Europium-131 | p (89%)

130Sm
β+ (?%)
131Sm
-
β+, p (?%)
130Pm
-id=Europium-134
β+
134Sm
-
β+, p (?%)
133Pm
-id=Europium-135
135Eu
134.94187(21)#
1.5(2) s
β+
135Sm
5/2+#

| | |-id=Europium-136 | β+ (99.91%)

136Sm
β+, p (0.09%)
135Pm
-id=Europium-136m
β+ (99.91%)
136Sm
-
β+, p (0.09%)
135Pm
-id=Europium-137
137Eu
136.9354307(47)
8.4(5) s
β+
137Sm
5/2+#

| | |-id=Europium-138 | 138Eu | 137.933709(30) | 5# s | | | 2−# | | |-id=Europium-138m | 12.1(6) s | β+ | 138Sm | 7−# | | |-id=Europium-139 | 139Eu | 138.929792(14) | 17.9(6) s | β+ | 139Sm | (11/2)− | | |-id=Europium-139m | 10(2) μs | IT | 139Eu | (7/2+) | | |-id=Europium-140

β+ (95.1%)
EC (4.9%)
-id=Europium-140m1
IT (99%)
140Eu
-
β+ (1%)
140Sm
-id=Europium-140m2
299.8(21) ns
IT
140Eu
(8+)

| | |-id=Europium-141 | 141Eu | 140.924932(14) | 40.7(7) s | β+ | 141Sm | 5/2+ | | |-id=Europium-141m | IT (86%)

141Eu
β+ (14%)
141Sm
-id=Europium-142
β+ (89.9%)
142Sm
-
EC (11.1%)
142Sm
-id=Europium-142m
1.223(8) min
β+
142Sm
8−

| | |-id=Europium-143 | 143Eu | 142.920299(12) | 2.59(2) min | β+ | 143Sm | 5/2+ | | |-id=Europium-143m | 50.0(5) μs | IT | 143Eu | 11/2− | | |-id=Europium-144 | 144Eu | 143.918819(12) | 10.2(1) s | β+ | 144Sm | 1+ | | |-id=Europium-144m | 1.0(1) μs | IT |144Eu | 8− | | |-id=Europium-145 | 145Eu | 144.9162727(33) | 5.93(4) d | β+ | 145Sm | 5/2+ | | |-id=Europium-145m | 490(30) ns | IT | 145Eu | 11/2− | | |-id=Europium-146 | 146Eu | 145.9172109(65) | 4.61(3) d | β+ | 146Sm | 4− | | |-id=Europium-146m | 235(3) μs | IT | 146Eu | 9+ | | |-id=Europium-147 | β+

147Sm
α (0.0022%)
143Pm
-id=Europium-147m
765(15) ns
IT
147Eu
11/2−

| | |-id=Europium-148 | β+

148Sm
α (9.4×10−7%)
144Pm
-id=Europium-148m
162(8) ns
IT
148Eu
9+

| | |-id=Europium-149 | 149Eu | 148.9179369(42) | 93.1(4) d | EC | 149Sm | 5/2+ | | |-id=Europium-149m | 2.45(5) μs | IT | 149Eu | 11/2− | | |-id=Europium-150 | 150Eu | 149.9197071(67) | 36.9(9) y | β+ | 150Sm | 5− | | |-id=Europium-150m | β− (89%)

150Gd
β+ (11%)
150Sm
-
IT (−8%)
150Eu
-id=Europium-151
151EuPrimordial radionuclide
150.9198566(13)
4.6(12)×1018 y
α
147Pm
5/2+
0.4781(6)

| |-id=Europium-151m | 58.9(5) μs | IT | 151Eu | 11/2− | | |-id=Europium-152 | β+ (72.08%)

152Sm
β− (27.92%)
152Gd
-id=Europium-152m1
β− (73%)
152Gd
-
β+ (27%)
152Sm
-id=Europium-152m2
940(80) ns
IT
152Eu
1−

| | |-id=Europium-152m3 | 165(10) ns | IT | 152Eu | 1+ | | |-id=Europium-152m4 | 384(10) ns | IT | 152Eu | 4+ | | |-id=Europium-152m5 | 95.8(4) min | IT | 152Eu | 8− | | |-id=Europium-153 | 153EuFission product | 152.9212368(13) | 5/2+ | 0.5219(6) | |-id=Europium-153m | 475(10) ns | IT | 153Eu | 19/2− | | |-id=Europium-154 | β− (99.98%)

154Gd
EC (0.02%)
154Sm
-id=Europium-154m1
2.2(1) μs
IT
154Eu
2+

| | |-id=Europium-154m2 | 46.3(4) min | IT | 154Eu | (8−) | | |- | 155Eu | 154.9228998(13) | 4.742(8) y | β− | 155Gd | 5/2+ | | |-id=Europium-156 | 156Eu | 155.9247630(38) | 15.19(8) d | β− | 156Gd | 0+ | | |-id=Europium-157 | 157Eu | 156.9254326(45) | 15.18(3) h | β− | 157Gd | 5/2+ | | |-id=Europium-158 | 158Eu | 157.9277822(22) | 45.9(2) min | β− | 158Gd | 1− | | |-id=Europium-159 | 159Eu | 158.9290995(46) | 18.1(1) min | β− | 159Gd | 5/2+ | | |-id=Europium-160 | 160Eu | 159.93183698(97) | 42.6(5) s | β− | 160Gd | (5−) | | |-id=Europium-160m | 30.8(5) s | IT | 160Eu | (1−) | | |-id=Europium-161 | 161Eu | 160.933664(11) | 26.2(23) s | β− | 161Gd | 5/2+# | | |-id=Europium-162 | 162Eu | 161.9369583(14) | ~10 s | β− | 162Gd | 1+# | | |-id=Europium-162m | 15.0(5) s | IT | 162Eu | (6+) | | |-id=Europium-163 | 163Eu | 162.93926551(97) | 7.7(4) s | β− | 163Gd | 5/2+# | | |-id=Europium-163m | 911(24) ns | IT | 163Eu | (13/2−) | | |-id=Europium-164 | 164Eu | 163.9428529(22) | 4.16(19) s | β− | 164Gd | 3−# | | |-id=Europium-165 | 165Eu | 164.9455401(56) | | β− | 165Gd | 5/2+# | | |-id=Europium-166 | β− (99.37%)

166Gd
β−, n (0.63%)
165Gd
-id=Europium-167
β− (98.05%)
167Gd
-
β−, n (1.95%)
166Gd
-id=Europium-168
β− (96.05%)
168Gd
-
β−, n (3.95%)
167Gd
-id=Europium-169
β− (85.38%)
169Gd
-
β−, n (14.62%)
168Gd
-id=Europium-170
β− (76%)
170Gd
-
β−, n (
169Gd

Europium-155

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.

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

References

(2007). "Search for α decay of natural europium". Nuclear Physics A.
(2014). "Discovery of the ¹⁵¹Eu α decay". [[Journal of Physics G: Nuclear and Particle Physics]].
"Adopted Levels for ¹⁵⁰Eu". NNDC Chart of Nuclides.
(2012). "Search for α decay of ¹⁵¹Eu to the first excited level of ¹⁴⁷Pm using underground γ-ray spectrometry". [[European Physical Journal A]].
(2019). "Experimental searches for rare alpha and beta decays". European Physical Journal A.
(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.

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