Isotopes of samarium
Naturally occurring samarium (Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (1.06×1011y) and 148Sm (7×1015y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm is also fairly long-lived (1.03×108y), but occurs naturally as only the tiniest trace remains from its original supernova nucleosynthesis.[1]
Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151Sm, which has a half-life of 96.6 years,[2] and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. This element also has twelve known isomers with the most stable being 141mSm (t1/2 22.6 minutes), 143m1Sm (t1/2 66 seconds) and 139mSm (t1/2 10.7 seconds).
The long lived isotopes,146Sm, 147Sm, and 148Sm primarily decay by alpha decay to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta minus decay to isotopes of europium
Isotopes of samarium are used in samarium-neodymium dating for determining the age relationships of rocks and meteorites.
151Sm is a medium-lived fission product and acts as a neutron poison in the nuclear fuel cycle. The stable fission product 149Sm is also a neutron poison.
Standard atomic mass: 150.36(2) u
Samarium-149
149Sm is an observed stable isotope of samarium (predicted to decay, but no decays have ever been observed, giving it a half-life several orders of magnitude longer than the age of the universe), and a fission product (yield 1.0888%) which is also a neutron-absorbing nuclear poison with significant effect on nuclear reactor operation, second only to 135Xe. Its neutron cross section is 40140 barns for thermal neutrons.
The equilibrium concentration (and thus the poisoning effect) builds to an equilibrium value in about 500 hours (about 20 days) of reactor operation, and since 149Sm is stable, the concentration remains essentially constant during further reactor operation.
Samarium-151
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 |
Thermal | Fast | 14 MeV | |
---|---|---|---|
232Th | not fissile | 0.399 ± 0.065 | 0.165 ± 0.035 |
233U | 0.333 ± 0.017 | 0.312 ± 0.014 | 0.49 ± 0.11 |
235U | 0.4204 ± 0.0071 | 0.431 ± 0.015 | 0.388 ± 0.061 |
238U | not fissile | 0.810 ± 0.012 | 0.800 ± 0.057 |
239Pu | 0.776 ± 0.018 | 0.797 ± 0.037 | ? |
241Pu | 0.86 ± 0.24 | 0.910 ± 0.025 | ? |
151
Sm
has a half-life of 96.6 years, undergoing low-energy beta decay, and has a fission product yield of 0.4203% for thermal neutrons and 235U, about 39% of 149Sm's yield. The yield is somewhat higher for 239Pu.
Its neutron absorption cross section for thermal neutrons is high at 15200 barns, about 38% of 149Sm's absorption cross section, or about 20 times that of 235U. Since the ratios between the production and absorption rates of151Sm and 149Sm are almost equal, the two isotopes should reach similar equilibrium concentrations. Since 149Sm reaches equilibrium in about 500 hours (20 days), 151Sm should reach equilibrium in about 50 days.
Since nuclear fuel is used for several years (burnup) in a nuclear power plant, the final amount of 151Sm in the spent nuclear fuel at discharge is only a small fraction of the total 151Sm produced during the use of the fuel. According to one study, the mass fraction of Sm-151 in spent fuel is about 0.0025 for heavy loading of MOX fuel and about half that for uranium fuel, which is roughly two orders of magnitude less than the mass fraction of about .15 for the medium-lived fission product Cs-137.[4] The decay energy of151Sm is also about an order of magnitude less than that of 137Cs. The low yield, low survival rate, and low decay energy mean that 151Sm has insignificant nuclear waste impact compared to the two main medium-lived fission products 137Cs and 90Sr.
Table
nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life[n 1] | decay mode(s)[5][n 2] |
daughter isotope(s)[n 3] |
nuclear spin |
representative isotopic composition (mole fraction) |
range of natural variation (mole fraction) |
---|---|---|---|---|---|---|---|---|---|
excitation energy | |||||||||
128Sm | 62 | 66 | 127.95808(54)# | 0.5# s | 0+ | ||||
129Sm | 62 | 67 | 128.95464(54)# | 550(100) ms | 5/2+# | ||||
130Sm | 62 | 68 | 129.94892(43)# | 1# s | β+ | 130Pm | 0+ | ||
131Sm | 62 | 69 | 130.94611(32)# | 1.2(2) s | β+ | 131Pm | 5/2+# | ||
β+, p (rare) | 130Nd | ||||||||
132Sm | 62 | 70 | 131.94069(32)# | 4.0(3) s | β+ | 132Pm | 0+ | ||
β+, p | 131Nd | ||||||||
133Sm | 62 | 71 | 132.93867(21)# | 2.90(17) s | β+ | 133Pm | (5/2+) | ||
β+, p | 132Nd | ||||||||
134Sm | 62 | 72 | 133.93397(21)# | 10(1) s | β+ | 134Pm | 0+ | ||
135Sm | 62 | 73 | 134.93252(17) | 10.3(5) s | β+ (99.98%) | 135Pm | (7/2+) | ||
β+, p (.02%) | 134Nd | ||||||||
135mSm | 0(300)# keV | 2.4(9) s | β+ | 135Pm | (3/2+,5/2+) | ||||
136Sm | 62 | 74 | 135.928276(13) | 47(2) s | β+ | 136Pm | 0+ | ||
136mSm | 2264.7(11) keV | 15(1) µs | (8-) | ||||||
137Sm | 62 | 75 | 136.92697(5) | 45(1) s | β+ | 137Pm | (9/2-) | ||
137mSm | 180(50)# keV | 20# s | β+ | 137Pm | 1/2+# | ||||
138Sm | 62 | 76 | 137.923244(13) | 3.1(2) min | β+ | 138Pm | 0+ | ||
139Sm | 62 | 77 | 138.922297(12) | 2.57(10) min | β+ | 139Pm | 1/2+ | ||
139mSm | 457.40(22) keV | 10.7(6) s | IT (93.7%) | 139Sm | 11/2- | ||||
β+ (6.3%) | 139Pm | ||||||||
140Sm | 62 | 78 | 139.918995(13) | 14.82(12) min | β+ | 140Pm | 0+ | ||
141Sm | 62 | 79 | 140.918476(9) | 10.2(2) min | β+ | 141Pm | 1/2+ | ||
141mSm | 176.0(3) keV | 22.6(2) min | β+ (99.69%) | 141Pm | 11/2- | ||||
IT (.31%) | 141Sm | ||||||||
142Sm | 62 | 80 | 141.915198(6) | 72.49(5) min | β+ | 142Pm | 0+ | ||
143Sm | 62 | 81 | 142.914628(4) | 8.75(8) min | β+ | 143Pm | 3/2+ | ||
143m1Sm | 753.99(16) keV | 66(2) s | IT (99.76%) | 143Sm | 11/2- | ||||
β+ (.24%) | 143Pm | ||||||||
143m2Sm | 2793.8(13) keV | 30(3) ms | 23/2(-) | ||||||
144Sm | 62 | 82 | 143.911999(3) | Observationally Stable[n 4] | 0+ | 0.0307(7) | |||
144mSm | 2323.60(8) keV | 880(25) ns | 6+ | ||||||
145Sm | 62 | 83 | 144.913410(3) | 340(3) d | EC | 145Pm | 7/2- | ||
145mSm | 8786.2(7) keV | 990(170) ns [0.96(+19-15) µs] |
(49/2+) | ||||||
146Sm[n 5] | 62 | 84 | 145.913041(4) | 1.03(5)×108 a | α | 142Nd | 0+ | Trace | |
147Sm[n 5][n 6][n 7] | 62 | 85 | 146.9148979(26) | 1.06(2)×1011 a | α | 143Nd | 7/2- | 0.1499(18) | |
148Sm[n 5] | 62 | 86 | 147.9148227(26) | 7(3)×1015 a | α | 144Nd | 0+ | 0.1124(10) | |
149Sm[n 6][n 8] | 62 | 87 | 148.9171847(26) | Observationally Stable[n 9] | 7/2- | 0.1382(7) | |||
150Sm | 62 | 88 | 149.9172755(26) | Observationally Stable[n 10] | 0+ | 0.0738(1) | |||
151Sm[n 6][n 8] | 62 | 89 | 150.9199324(26) | 96.6(24) a | β- | 151Eu | 5/2- | ||
151mSm | 261.13(4) keV | 1.4(1) µs | (11/2)- | ||||||
152Sm[n 6] | 62 | 90 | 151.9197324(27) | Observationally Stable[n 11] | 0+ | 0.2675(16) | |||
153Sm[n 6] | 62 | 91 | 152.9220974(27) | 46.284(4) h | β- | 153Eu | 3/2+ | ||
153mSm | 98.37(10) keV | 10.6(3) ms | IT | 153Sm | 11/2- | ||||
154Sm[n 6] | 62 | 92 | 153.9222093(27) | Observationally Stable[n 12] | 0+ | 0.2275(29) | |||
155Sm | 62 | 93 | 154.9246402(28) | 22.3(2) min | β- | 155Eu | 3/2- | ||
156Sm | 62 | 94 | 155.925528(10) | 9.4(2) h | β- | 156Eu | 0+ | ||
156mSm | 1397.55(9) keV | 185(7) ns | 5- | ||||||
157Sm | 62 | 95 | 156.92836(5) | 8.03(7) min | β- | 157Eu | (3/2-) | ||
158Sm | 62 | 96 | 157.92999(8) | 5.30(3) min | β- | 158Eu | 0+ | ||
159Sm | 62 | 97 | 158.93321(11) | 11.37(15) s | β- | 159Eu | 5/2- | ||
160Sm | 62 | 98 | 159.93514(21)# | 9.6(3) s | β- | 160Eu | 0+ | ||
161Sm | 62 | 99 | 160.93883(32)# | 4.8(8) s | β- | 161Eu | 7/2+# | ||
162Sm | 62 | 100 | 161.94122(54)# | 2.4(5) s | β- | 162Eu | 0+ | ||
163Sm | 62 | 101 | 162.94536(75)# | 1# s | β- | 163Eu | 1/2-# | ||
164Sm | 62 | 102 | 163.94828(86)# | 500# ms | β- | 164Eu | 0+ | ||
165Sm | 62 | 103 | 164.95298(97)# | 200# ms | β- | 165Eu | 5/2-# |
- ^ Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
- ^ Abbreviations:
EC: Electron capture
IT: Isomeric transition - ^ Bold for stable isotopes, bold italics for nearly stable isotopes (half-life longer than the age of the universe)
- ^ Believed to undergo α decay to 140Nd or β+β+ decay to 144Nd
- ^ a b c Primordial radioisotope
- ^ a b c d e f Fission product
- ^ Used in Samarium-neodymium dating
- ^ a b Neutron poison in reactors
- ^ Believed to undergo α decay to 145Nd with a half-life over 2×1015 years
- ^ Believed to undergo α decay to 146Nd
- ^ Believed to undergo α decay to 148Nd
- ^ Believed to undergo β-β- decay to 154Gd with a half-life over 2.3×1018 years
Notes
- Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
- Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
- Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
References
- Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
{{cite journal}}
: CS1 maint: multiple names: authors list (link)
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). 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:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.
{{cite journal}}
: Unknown parameter|laysummary=
ignored (help)
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
{{cite journal}}
: CS1 maint: multiple names: authors list (link) - National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
{{cite web}}
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(help) - N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.
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- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
- ^ Samir Maji; et al. (2006). "Separation of samarium and neodymium: a prerequisite for getting signals from nuclear synthesis". Analyst. 131 (12): 1332–1334. Bibcode:2006Ana...131.1332M. doi:10.1039/b608157f. PMID 17124541.
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instead. - ^ http://www-nds.iaea.org/sgnucdat/c3.htm Cumulative Fission Yields, IAEA
- ^ http://www.nea.fr/html/pt/docs/iem/jeju02/session5/SectionV-12.pdf Figure 2, page 6
- ^ http://www.nucleonica.net/unc.aspx