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Isotopes of samarium
Isotopes of samarium
Isotopes of samarium
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Isotopes of samarium (62Sm)
Main isotopes[1] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
144Sm 3.08% stable
145Sm synth 340 d ε 145Pm
146Sm trace 9.20×107 y[2] α 142Nd
147Sm 15% 1.066×1011 y α 143Nd
148Sm 11.3% 6.3×1015 y α 144Nd
149Sm 13.8% stable
150Sm 7.37% stable
151Sm synth 94.6 y β− 151Eu
152Sm 26.7% stable
153Sm synth 46.285 h β− 153Eu
154Sm 22.7% stable
Standard atomic weight Ar°(Sm)

Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.066×1011 y) and 148Sm (6.3×1015 y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm (9.20×107 y)[2] is also fairly long-lived, but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an extinct radionuclide.[5] It is the longest-lived nuclide that has not yet been confirmed to be primordial. Its instability is due to having 84 neutrons (two more than 82, which is a magic number corresponding to a stable neutron configuration), and so it may emit an alpha particle (which has 2 neutrons) to form neodymium-142 with 82 neutrons.

Other than those, the longest-lived radioisotopes are 151Sm, which has a half-life of 94.6 years,[6] and 145Sm, which has a half-life of 340 days. All of the remaining radioisotopes, which range from 129Sm to 168Sm, have half-lives that are less than two days, and the majority of these have half-lives that are less than 48 seconds. The most stable of the known isomers is 141mSm (half-life 22.6 minutes).

The long-lived isotopes, 146Sm, 147Sm, and 148Sm, decay by alpha emission to isotopes of neodymium. Lighter unstable isotopes of samarium primarily decay by electron capture to isotopes of promethium, while heavier ones decay by beta decay to isotopes of europium. A 2012 paper[7] revising the estimated half-life of 146Sm from 10.3(5)×107 y to 6.8(7)×107 y was retracted (due to an experimental mistake) in 2023,[7][8] and the current, more accurate, value published subsequently.

The isotope 147Sm is used in samarium–neodymium dating and as mentioned the extinct 146Sm can also be used for dating.

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.

Samarium is the lightest element with even atomic number with no theoretically stable isotopes (all isotopes of it can energetically decay by the alpha, beta, or double-beta modes), other such elements are those with atomic numbers > 66 (dysprosium, which has the heaviest theoretically stable nuclide, 164Dy).

List of isotopes

[edit]


Nuclide
[n 1] 		Z N Isotopic mass (Da)[9]
[n 2][n 3] 		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)
Excitation energy[n 5] Normal proportion[1] Range of variation
129Sm 62 67 128.95456(54)# 550(100) ms β+ (?%) 129Pm (1/2+,3/2+)
β+, p (?%) 128Nd
130Sm 62 68 129.94879(43)# 1# s 0+
131Sm 62 69 130.94602(43)# 1.2(2) s β+ 131Pm 5/2+#
β+, p (?%) 130Nd
132Sm 62 70 131.94081(32)# 4.0(3) s β+ 132Pm 0+
133Sm 62 71 132.93856(32)# 2.89(16) s β+ (?%) 133Pm (5/2+)
β+, p (?%) 132Nd
133mSm 120(60)# keV 3.5(4) s β+ 133Pm (1/2−)
134Sm 62 72 133.93411(21)# 9.5(8) s β+ 134Pm 0+
135Sm 62 73 134.93252(17) 10.3(5) s β+ (99.98%) 135Pm (7/2+)
β+, p (0.02%) 134Nd
136Sm 62 74 135.928276(13) 47(2) s β+ 136Pm 0+
136mSm 2264.7(11) keV 15(1) μs IT 136Sm (8−)
137Sm 62 75 136.927008(31) 45(1) s β+ 137Pm (9/2−)
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 457.38(23) 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 79 140.9184815(92) 10.2(2) min β+ 141Pm 1/2+
141mSm 175.9(3) keV 22.6(2) min β+ (99.69%) 141Pm 11/2−
IT (0.31%) 141Sm
142Sm 62 80 141.9152094(20) 72.49(5) min EC (>95%) 142Pm 0+
β+ (<5%)
142m1Sm 2372.1(4) keV 170(2) ns IT 142Sm 7−
142m2Sm 3662.2(7) keV 480(60) ns IT 142Sm 10+
143Sm 62 81 142.9146348(30) 8.75(6) min EC (60.0%) 143Pm 3/2+
β+ (40.0%) 143Pm
143m1Sm 753.99(16) keV 66(2) s IT (99.76%) 143Sm 11/2−
β+ (0.24%) 143Pm
143m2Sm 2793.8(13) keV 30(3) ms IT 143Sm 23/2−
144Sm 62 82 143.9120063(16) Observationally stable[n 10] 0+ 0.0308(4)
144mSm 2323.60(8) keV 880(25) ns IT 144Sm 6+
145Sm 62 83 144.9134172(16) 340(3) d EC 145Pm 7/2−
145mSm 8815(1) keV 3.52(16) μs IT 145Sm 49/2+
146Sm 62 84 145.9130468(33) 9.20(26)×107 y[2] α 142Nd 0+ Trace
147Sm[n 11][n 12][n 13] 62 85 146.9149044(14) 1.066(5)×1011 y α 143Nd 7/2− 0.1500(14)
148Sm[n 11] 62 86 147.9148292(13) 6.3(13)×1015 y α 144Nd 0+ 0.1125(9)
149Sm[n 12][n 14] 62 87 148.9171912(12) Observationally stable[n 15] 7/2− 0.1382(10)
150Sm 62 88 149.9172820(12) Observationally stable[n 16] 0+ 0.0737(9)
151Sm[n 12][n 14] 62 89 150.9199389(12) 94.6(6) y β− 151Eu 5/2−
151mSm 261.13(4) keV 1.4(1) μs IT 151Sm (11/2)−
152Sm[n 12] 62 90 151.9197386(11) Observationally stable[n 17] 0+ 0.2674(9)
153Sm[n 12] 62 91 152.9221036(11) 46.2846(23) h β− 153Eu 3/2+
153mSm 98.39(10) keV 10.6(3) ms IT 153Sm 11/2−
154Sm[n 12] 62 92 153.9222158(14) Observationally stable[n 18] 0+ 0.2274(14)
155Sm 62 93 154.9246466(14) 22.18(6) min β− 155Eu 3/2−
155m1Sm 16.5467(19) keV 2.8(5) μs IT 155Sm 5/2+
155m2Sm 538.03(19) keV 1.00(8) μs IT 155Sm 11/2−
156Sm 62 94 155.9255382(91) 9.4(2) h β− 156Eu 0+
156mSm 1397.55(9) keV 185(7) ns IT 156Sm 5−
157Sm 62 95 156.9284186(48) 8.03(7) min β− 157Eu 3/2−#
158Sm 62 96 157.9299493(51) 5.30(3) min β− 158Eu 0+
159Sm 62 97 158.9332171(64) 11.37(15) s β− 159Eu 5/2−
159mSm 1276.5(8) keV 116(8) ns IT 159Sm (15/2+)
160Sm 62 98 159.9353370(21) 9.6(3) s β− 160Eu 0+
160m1Sm 1361.3(4) keV 120(46) ns IT 160Sm (5−)
160m2Sm 2757.3(4) keV 1.8(4) μs IT 160Sm (11+)
161Sm 62 99 160.9391601(73) 4.8(4) s β− 161Eu 7/2+#
161mSm 1388.1(6) keV 2.6(4) μs IT 161Sm (17/2−)
162Sm 62 100 161.9416217(38) 2.7(3) s β− 162Eu 0+
162mSm 1009.4(5) keV 1.78(7) μs IT 162Sm (4−)
163Sm 62 101 162.9456791(79) 1.744+0.180
−0.204 s[11] 		β− 163Eu 1/2−#
β−, n (<0.1%) 162Eu
164Sm 62 102 163.9485501(44) 1.422+0.54
−0.59 s[11] 		β− 164Eu 0+
β−, n (<0.7%) 163Eu
164mSm 1485.5(12) keV 600(140) ns IT 164Sm (6−)
165Sm 62 103 164.95329(43)# 592+51
−55 ms[11] 		β− (98.64%) 165Eu 5/2−#
β−, n (1.36%) 164Eu
166Sm 62 104 165.95658(43)# 396+56
−63 ms[11] 		β− (95.62%) 166Eu 0+
β−, n (4.38%) 165Eu
167Sm 62 105 166.96207(54)# 334+83
−78 ms[11] 		β− 167Eu 7/2−#
β−, n (<16%) 166Eu
168Sm 62 106 167.96603(32)# 353+210
−164 ms[11] 		β− 168Eu 0+#
β−, n (<21%) 167Eu
This table header & footer:
  1. ^ mSm – 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. ^ a b c # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  6. ^ Modes of 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. ^ Believed to undergo β+β+ decay to 144Nd
  11. ^ a b Primordial radioisotope
  12. ^ a b c d e f Fission product
  13. ^ Used in Samarium–neodymium dating
  14. ^ a b Neutron poison in reactors
  15. ^ Believed to undergo α decay to 145Nd with a half-life over 2×1015 years[10]
  16. ^ Believed to undergo α decay to 146Nd[10]
  17. ^ Believed to undergo α decay to 148Nd[10]
  18. ^ Believed to undergo β−β− decay to 154Gd with a half-life over 2.3×1018 years

Samarium-149

[edit]

Samarium-149 (149Sm) is an observationally stable isotope of samarium (predicted to decay, but no decays have ever been observed, giving it a half-life at least several orders of magnitude longer than the age of the universe), and a product of the decay chain from the fission product 149Nd (yield 1.0888%). 149Sm is 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. This contrasts with xenon-135, which accumulates from the beta decay of iodine-135 (a short lived fission product) and has a high neutron cross section, but itself decays with a half-life of 9.2 hours (so does not remain in constant concentration long after the reactor shutdown), causing the so-called xenon pit.

Samarium-151

[edit]
Medium-lived fission products
Nuclide t1⁄2 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. ^ a b c 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: Br-85 → Kr-85m → Rb-85.
  5. ^ Has decay energy 546 keV; its decay product Y-90 has decay energy 2.28 MeV with weak gamma branching.
Yield, % per fission[12]
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 ?

Samarium-151 (151Sm) has a half-life of 94.6 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 of 151Sm 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. As this is still much shorter than its radioactive half-life, decay will hardly affect this equilibrium while in the reactor.

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 151Sm 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 0.15 for the medium-lived fission product 137Cs.[13] The decay energy of 151Sm 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.

Samarium-153

[edit]

Samarium-153 (153Sm) has a half-life of 46.285 hours, undergoing β− decay into stable 153Eu. As a component of samarium lexidronam, it is used in palliation of bone cancer.[14] It is treated by the body in a similar manner to calcium, and it localizes selectively to bone.

See also

[edit]

Daughter products other than samarium

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Isotopes of samarium

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Naturally occurring consists of seven isotopes, five of which—^{144}Sm (3.07%), ^{149}Sm (13.82%), ^{150}Sm (7.38%), ^{152}Sm (26.75%), and ^{154}Sm (22.75%)—are , while the remaining two, ^{147}Sm (14.99%) and ^{148}Sm (11.24%), are radioactive with extremely long half-lives of (1.0625 ± 0.0038) × 10^{11} years and approximately 7 × 10^{15} years, respectively. In total, 33 isotopes and isomers of ranging from mass numbers 129 to 162 have been observed, most of which are artificially produced in nuclear reactions and exhibit with half-lives spanning from microseconds to years. Among the notable properties of samarium isotopes, ^{149}Sm stands out due to its exceptionally high thermal neutron absorption cross-section of about 40,000 barns, making it a valuable in control rods to regulate fission reactions. The long-lived ^{147}Sm is widely used in samarium-neodymium for dating ancient rocks and meteorites, as its to ^{143}Nd provides insights into Earth's crustal evolution over billions of years. Additionally, short-lived isotopes like ^{153}Sm ( 46.3 hours) are employed in targeted for treating bone metastases in cancer patients, where it delivers beta radiation while binding to in bone tissue. Other samarium isotopes, such as ^{151}Sm ( 90 years), arise as fission products in and contribute to long-term management challenges.

Overview

Natural occurrence and abundances

Natural samarium consists of five stable isotopes—^{144}Sm, ^{149}Sm, ^{150}Sm, ^{152}Sm, and ^{154}Sm—and two long-lived radioisotopes, ^{147}Sm and ^{148}Sm. These isotopes form the natural isotopic composition of the element, with the following relative abundances (in atom percent):
IsotopeAbundance (%)
^{144}Sm3.08(4)
^{147}Sm15.00(14)
^{148}Sm11.25(9)
^{149}Sm13.82(10)
^{150}Sm7.37(9)
^{152}Sm26.74(9)
^{154}Sm22.74(14)
The of samarium, 150.36(2), is determined by the weighted average of these isotopic masses and their abundances. Samarium isotopes are primordial, originating from in stars through slow () and rapid (r-process) neutron capture reactions. In nature, samarium occurs primarily in rare earth minerals such as and , where it is associated with other lanthanides. Isotopic ratios of samarium can exhibit slight variations due to geological processes or nucleosynthetic heterogeneity observed in meteorites.

General properties and production

Samarium, with Z = 62, has 34 known isotopes ranging in mass number from 129 to 162. These isotopes span a wide variety of nuclear properties, including , long-lived radioactive, and short-lived radioactive forms. Due to the even proton number, isotopes exhibit no odd-even staggering in stability beyond the standard effects, as the protons are always paired, leading to even-even nuclei (even N) being particularly compared to odd- neighbors. Stable isotopes of samarium are obtained by enrichment from natural ore, primarily through electromagnetic isotope separation (calutrons), which exploits mass differences in magnetic fields. Radioactive isotopes, in contrast, are synthesized via nuclear reactions: on stable samarium targets in reactors produces neutron-richer isotopes, as exemplified by the production of ^{153}Sm through the reaction ^{152}Sm(n,\gamma)^{153}Sm, while bombardment in accelerators generates neutron-deficient isotopes. Half-lives among isotopes show clear trends influenced by nuclear structure, with the longest durations observed in even-even nuclei like ^{148}Sm (approximately 7 \times 10^{15} years), reflecting enhanced stability from paired nucleons, whereas neutron-deficient isotopes exhibit the shortest half-lives, ranging down to 0.55 seconds for ^{129}Sm. These patterns are well-explained by nuclear shell models, where shell effects near neutron numbers N = 88–90 contribute to increased binding energies and stability, particularly in the deformed rare earth region, as seen in systematic studies of and higher-order correlations in isotopes. Isotopes beyond the natural abundance range, such as ^{145}Sm and ^{155}Sm, are artificially produced; for instance, ^{145}Sm results from on ^{144}Sm in reactors, while ^{155}Sm arises from successive s on ^{154}Sm, enabling studies of nuclear structure and applications in research.

Stable isotopes

Samarium-144

Samarium-144 (62144Sm^{144}_{62}\mathrm{Sm}) is the lightest isotope of and features an even-even nucleus configuration, resulting in a ground-state nuclear spin of 0+0^+ and exceptional stability against both and pathways. In natural samarium, 144Sm^{144}\mathrm{Sm} has the lowest abundance among the stable isotopes at 3.07(7)%. This isotope originates primarily from the p-process (gamma-process) nucleosynthesis, occurring in explosive astrophysical sites such as core-collapse supernovae, where it forms through photodisintegration of more neutron-rich seed nuclei like 148Gd^{148}\mathrm{Gd}. Key physical properties include an isotopic mass of 143.9120065(21) u, which contributes to precise in experiments. Due to its exclusive p-process origin, 144Sm^{144}\mathrm{Sm} is valuable in isotopic analyses of meteorites and stars to probe the efficiency and sites of gamma-process , providing constraints on supernova models and solar system formation. In laboratory settings, 144Sm^{144}\mathrm{Sm} (often enriched) undergoes thermal to yield 145Sm^{145}\mathrm{Sm}, a radioisotope with a 340-day employed in research and precise determinations for nuclear data validation.

Samarium-149

is a of with a natural abundance of 13.82(7)% in samarium samples on Earth. Its atomic mass is 148.9171921(18) u, and it has a nuclear spin of 7/2⁻. This isotope is one of seven stable nuclides of samarium and plays a significant role in nuclear physics due to its interaction with neutrons. Samarium-149 exhibits an exceptionally high thermal neutron capture cross-section of 40,140 barns, the largest among all stable isotopes. This property arises from a strong at low neutron energies, making it an effective absorber of neutrons. In nuclear reactors, this leads to the conversion of samarium-149 into samarium-150 through the (n,γ) radiative capture reaction: ^{149}Sm + n → ^{150}Sm + γ. The resulting samarium-150 has a much lower capture cross-section, allowing the process to continue until an equilibrium is established between production and absorption rates. In operating nuclear reactors fueled by , samarium-149 acts as a potent , absorbing neutrons that would otherwise sustain the fission and thereby reducing overall reactivity. Its concentration reaches equilibrium after approximately 500 hours in high-flux environments, where the rate of balances the rate of formation from fission products like promethium-149. This equilibrium buildup must be accounted for in design and efficiency calculations, as it contributes a reactivity penalty of several percent in typical pressurized water reactors. Historically, samarium-149's neutron absorption properties were observed in early nuclear experiments, including those analyzing fission product yields from uranium-235 irradiation in test reactors during the mid-20th century. In , samarium-149 contributes to the () in , where its high cross-section influences isotopic branching ratios near the samarium region and helps model heavy element production in stars.

Samarium-150

Samarium-150 (¹⁵⁰Sm) is one of the five stable isotopes of , characterized by an of 149.9172829(18) u, a natural abundance of 7.38(1)%, and a nuclear spin and parity of 0⁺. This even-even nucleus exhibits no and contributes to the overall atomic weight of in terrestrial samples. Naturally, ¹⁵⁰Sm is produced exclusively through the slow process (s-process) during the phase of low- to intermediate-mass , where it forms via sequential captures and beta decays along the valley of stability. Unlike some neighboring samarium isotopes, it receives no significant contribution from the rapid process (r-process) due to neutron-rich pathways bypassing this mass number in explosive environments. Synthetically, ¹⁵⁰Sm is generated through on ¹⁴⁹Sm, a reaction with a high cross-section that is relevant in nuclear reactors and experiments. The ratio of ¹⁵⁰Sm to ¹⁴⁹Sm serves as a key for quantifying fluence in nuclear reactors and deposits, as the large capture cross-section of ¹⁴⁹Sm (approximately 40,000 barns) leads to measurable isotopic shifts under exposure. This application exploits the stability of both isotopes to reconstruct historical fluxes without reliance on short-lived intermediaries. In , ¹⁵⁰Sm finds minor use in tracing distributions in environmental and geological contexts, such as cores or meteoritic materials, where its stable signature aids in distinguishing anthropogenic inputs from natural sources when combined with other samarium isotopes.

Samarium-152

Samarium-152 (^{152}\text{SM}) is the most abundant stable isotope of , constituting 26.75(16)% of naturally occurring samarium. Its standard is 151.9197397(18) u, and as an even-even nucleus with 62 protons and 90 neutrons, it possesses a nuclear ground-state spin and parity of 0^+. This configuration contributes to its exceptional stability, with no known decay modes. Due to its prevalence, ^{152}\text{Sm} serves as the primary contributor to the of , which is 150.36(2) u. In natural mineral systems, such as rare-earth-bearing phosphates like , the chemical behavior of samarium is largely governed by the properties of ^{152}\text{Sm}, as its high abundance dominates the isotopic mixture and influences mass-dependent fractionation effects in geochemical processes. In , ^{152}\text{Sm} functions as the key reference isotope for isotopic dilution techniques used to quantify total concentrations in environmental, geological, and biological samples, enabling high-precision measurements by normalizing against spiked isotopes like ^{149}\text{Sm}. Astrophysically, ^{152}\text{Sm} is produced through neutron-capture processes in stars, with the in stars contributing approximately 23% to its solar system abundance according to classical models, while the r-process dominates the remainder; isotopic ratios involving ^{152}\text{Sm} help constrain stellar densities and conditions in these environments.

Samarium-154

Samarium-154 (154^{154}Sm) is one of the five stable of , characterized by an of 153.9222169(20) u, a nuclear spin of 0+0^+, and a natural abundance of 22.75(29)%. As the second-most abundant stable samarium isotope, it contributes significantly to the element's overall isotopic composition in terrestrial materials. This isotope forms primarily through rapid neutron-capture (r-process) nucleosynthesis in astrophysical environments, exhibiting a higher r-process contribution relative to lighter stable isotopes such as 148^{148}Sm and 150^{150}Sm, which originate almost exclusively from the slow neutron-capture (). 154^{154}Sm plays a role in owing to its moderate thermal cross-section of 210 ± 10 barns, enabling the production of the radioactive 155^{155}Sm for quantitative detection of in geological and environmental samples without the interference seen in high-cross-section isotopes like 149^{149}Sm. In spectroscopic applications, isotopic shifts in 's atomic spectrum, notably the shift of approximately 40 cm−1^{-1} between 152^{152}Sm and 154^{154}Sm lines, facilitate the identification and selective separation of within mixtures using laser-based techniques.

Long-lived radioactive isotopes

Samarium-146

Samarium-146 is a radioactive isotope that decays exclusively via alpha emission to the stable isotope neodymium-142, with a branching ratio of 100%. Its half-life was precisely measured in 2024 as 9.20×1079.20 \times 10^{7} years, with an uncertainty of ±2.6×106\pm 2.6 \times 10^{6} years (2.76% combined standard uncertainty). This value was determined using cryogenic decay energy spectroscopy on samples produced via proton irradiation of tantalum targets, confirming pure alpha decay and resolving prior discrepancies. The updated half-life revises earlier estimates, notably rejecting a 2012 measurement of 6.8×1076.8 \times 10^{7} years that was retracted due to sample contamination issues. Samarium-146 is extinct and does not occur naturally on today, as its is much shorter than the age of the Solar System. It was present in the early solar system as a produced by . For experimental purposes, such as calibration and isotopic standard preparation, samarium-146 is artificially produced in nuclear reactors through on samarium-145 or in particle accelerators via reactions on heavy targets like . Reactor production involves thermal neutron irradiation, allowing accumulation of measurable quantities despite the isotope's long . In , samarium-146 serves as the parent in the short-lived 146Sm^{146}\text{Sm}-142Nd^{142}\text{Nd} system, ideal for differentiation events in meteorites and lunar samples spanning approximately 10810^{8} years after solar system formation. The decay constant is λ=ln⁡2t1/2\lambda = \frac{\ln 2}{t_{1/2}}, approximately 7.53×10−97.53 \times 10^{-9} year−1^{-1} based on the 2024 . Ages are determined using the fossil isochron method, plotting the ratio of 142Nd/144Nd^{142}\text{Nd}/^{144}\text{Nd} against 144Sm/144Nd^{144}\text{Sm}/^{144}\text{Nd}, where the slope relates to the initial 146Sm/144Sm^{146}\text{Sm}/^{144}\text{Sm} ratio and the time elapsed since system closure. This method has constrained the timing of processes such as lunar mantle formation and accretion to within 20-50 million years of solar system inception.

Samarium-147

Samarium-147 is a primordial radioactive of that undergoes to neodymium-143 with a branching ratio of 100%. Its is (1.0625 ± 0.0038) × 10^{11} years. This long half-life makes it suitable for geochronological applications over billion-year timescales. In natural , ^{147}Sm constitutes 14.99% of the total abundance and originates from the rapid neutron-capture process (r-process) in core-collapse supernovae, contributing to the primordial inventory of heavy elements in the solar system. As a long-lived , it has persisted since the formation of the without significant depletion from decay. ^{147}Sm plays a central role in the samarium-neodymium (Sm-Nd) isotope system, widely used for the formation and of the continental crust up to approximately 4 billion years ago (Ga). The chondritic uniform reservoir () parent-daughter ratio is ^{147}Sm/^{144}Sm = 0.1967, providing a reference for mantle-derived materials. The radiogenic is described by the equation: 143Nd144Nd=(143Nd144Nd)initial+147Sm144Sm(eλt−1)\frac{^{143}\text{Nd}}{^{144}\text{Nd}} = \left( \frac{^{143}\text{Nd}}{^{144}\text{Nd}} \right)_{\text{initial}} + \frac{^{147}\text{Sm}}{^{144}\text{Sm}} (e^{\lambda t} - 1) where λ=ln⁡(2)/(1.0625×1011)\lambda = \ln(2) / (1.0625 \times 10^{11}) year^{-1}. This system has been instrumental in tracing mantle evolution, including depletion events and crustal growth rates, as well as dating ancient lunar rocks to constrain early solar system .

Samarium-148

Samarium-148 (^{148}\text{Sm}) is one of the two long-lived radioactive isotopes of found in nature, constituting 11.24% of the element's natural abundance. As an even-even nucleus with 62 protons and 86 s, it possesses a ground-state spin and parity of 0^+, which contributes to its exceptional stability compared to other radioactive samarium isotopes, making it the most stable among them. This configuration places it near the shell closure at N=82, enhancing nuclear binding and delaying decay. The of ^{148}\text{Sm} is theoretically estimated at 7 \times 10^{15} years, with uncertainties indicating a value greater than 10^{15} years; no decay events have been experimentally observed due to the extraordinarily long timescale. It is predicted to undergo to ^{144}\text{Nd}, with a total energy release (Q-value) of approximately 1.986 MeV. Theoretical models predict this low Q-value results in a highly suppressed branching ratio for , primarily due to the substantial in this heavy nucleus, which hinders the emission of the despite the even-even structure favoring it over other modes. ^{148}\text{Sm} is produced exclusively via the slow neutron-capture process (s-process) in asymptotic giant branch stars, as it is shielded from rapid neutron-capture (r-process) contributions by the stable isotope ^{148}\text{Nd}. Isotopic anomalies observed in samarium, particularly in r-process-dominated isotopes like ^{152}\text{Sm} and ^{154}\text{Sm}, are analyzed relative to s-process reference isotopes such as ^{148}\text{Sm} to constrain models of supernova nucleosynthesis yields and the injection of presolar material into the early solar nebula. These anomalies, detected in meteoritic calcium-aluminum-rich inclusions, reflect heterogeneous distributions of r-process products from supernovae, with ^{148}\text{Sm} serving as a baseline for normalizing deviations. As an even-even nucleus, ^{148}\text{Sm} is theoretically a candidate for to ^{148}\text{Cd}, but no such events have been observed, consistent with the dominance of the predicted alpha mode and the isotope's extreme longevity.

Short-lived isotopes of interest

Samarium-151

is a radioactive of with a relatively long among fission products, primarily produced as a fission product in nuclear reactors through the beta decay chain from direct fission fragments around mass 151. It undergoes beta-minus decay to the stable isotope europium-151 with a (Q-value) of 76.43(7) keV. The of has been measured as 94.7(6) years, making it one of the longer-lived fission products and contributing to sustained low-level activity over decades. In thermal neutron-induced fission of , the cumulative fission yield for samarium-151 is 0.4186%, which includes contributions from precursor nuclides in the mass 151 chain as well as minor direct production and on samarium-149. This yield is notably lower than that of the adjacent samarium-149 but still significant for dynamics. The independent (direct) fission yield is much smaller at approximately 0.000022%, emphasizing the role of accumulation. Samarium-151 serves as an important in nuclear reactors due to its exceptionally high thermal capture cross-section of 15,200 barns for the (n,γ) reaction producing samarium-152, which is about 20 times that of uranium-235. This absorption competes with decay, leading to an equilibrium concentration after roughly 50 days of operation, beyond which further buildup is balanced by removal via capture and decay. The concentration dynamics follow the standard buildup equation for a radioactive with absorption: dNdt=Y⋅F−λN−σϕN\frac{dN}{dt} = Y \cdot F - \lambda N - \sigma \phi N where NN is the atom of , YY the cumulative fission yield, FF the fission rate, λ\lambda the decay constant, σ\sigma the capture cross-section, and ϕ\phi the . This equilibrium affects reactor reactivity, particularly in longer irradiation cycles. In , samarium-151's 94.7-year results in persistent beta activity, representing a notable of the long-term radiotoxicity and complicating strategies. Its chemical behavior as a raises concerns for solubility and potential migration in repository environments, necessitating evaluation in performance assessments for disposal. Concentrations in spent fuel can reach levels that influence shielding and handling protocols over centuries.

Samarium-153

Samarium-153 is a of with a of 46.3 hours, decaying 100% through beta-minus emission to stable europium-153. The maximum beta energy is 0.81 MeV, enabling targeted energy deposition in tissues. Accompanying gamma emission at 103 keV with 28% intensity allows for and dosimetry verification during therapeutic applications. Production of samarium-153 involves of an enriched samarium-152 target in a , following the reaction ^{152}Sm(n,γ)^{153}Sm. High-purity ^{152}Sm (typically >98% enriched) is used as the target material, such as Sm(NO_3)_3, irradiated in high fluxes of 2.0–2.5 × 10^{14} n/cm²/s for 2–3 days. Yields can reach approximately 5 × 10^4 Ci/g (1.87 TBq/mg) through optimized and subsequent mass separation techniques like laser resonance ionization. In , samarium-153 is chelated with ethylenediaminetetramethylene (EDTMP) to form Quadramet (samarium-153 lexidronam), a approved by the FDA in for palliation of from osteoblastic metastatic lesions that enhance on scans. The agent preferentially accumulates in of metastatic sites, delivering localized beta radiation to alleviate pain while minimizing damage to surrounding healthy tissue. The standard administered dose is 1 mCi/kg (37 MBq/kg), given intravenously over one minute. Dosimetric considerations for samarium-153-EDTMP highlight its suitability for bone-targeted , with the beta particles exhibiting an average range of approximately 0.8 mm in , confining the dose to metastatic lesions. The effective in metastases is approximately the physical of 46.3 hours, due to long biological retention (mean biological ∼520 hours), influenced by rapid clearance (initial of 5.5 minutes) and prolonged skeletal retention. This contributes to reduced marrow toxicity compared to longer-lived isotopes. The follows the standard exponential law, where the activity A(t)A(t) at time tt is given by A(t)=A0e−λt,A(t) = A_0 e^{-\lambda t}, with decay constant λ=ln⁡246.3\lambda = \frac{\ln 2}{46.3} h⁻¹, ensuring predictable dose delivery over the isotope's lifespan.

References

  1. https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=Sm
  2. https://www.osti.gov/servlets/purl/1644013
  3. https://remm.hhs.gov/ANL_ContaminantFactSheets_All_070418.pdf
  4. https://pubchem.ncbi.nlm.nih.gov/compound/Samarium_-Radioactive
  5. https://hpschapters.org/northcarolina/NSDS/samarium.pdf
  6. https://ciaaw.org/samarium.htm
  7. https://www.aanda.org/articles/aa/abs/2007/08/aa6231-06/aa6231-06.html
  8. https://pubchem.ncbi.nlm.nih.gov/compound/Samarium
  9. https://jast-journal.springeropen.com/articles/10.1186/s40543-024-00424-6
  10. https://arxiv.org/abs/1201.4159
  11. https://link.aps.org/doi/10.1103/PhysRevC.111.024301
  12. https://www.isotopes.gov/production-methods
  13. https://pmc.ncbi.nlm.nih.gov/articles/PMC8326506/
  14. https://www.britannica.com/science/samarium
  15. https://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Sm144
  16. https://www.aanda.org/articles/aa/full/2007/08/aa6231-06/aa6231-06.right.html
  17. https://iopscience.iop.org/article/10.1088/0004-637X/739/2/93
  18. https://www.sciencedirect.com/science/article/abs/pii/002219026880106X
  19. https://www.sciencedirect.com/science/article/pii/S0969804321003742
  20. https://www.osti.gov/pages/servlets/purl/2585324
  21. https://www.nuclear-power.com/nuclear-power/reactor-physics/reactor-operation/samarium-149/
  22. https://www.nrc.gov/docs/ML1125/ML11258A296.pdf
  23. https://link.aps.org/doi/10.1103/PhysRevC.73.015802
  24. https://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Sm150
  25. https://ned.ipac.caltech.edu/level5/Glossary/Jaschek/Sm.html
  26. https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lareport/LA-UR-05-8682
  27. https://www.sciencedirect.com/science/article/abs/pii/S0016703700005676
  28. https://www.sciencedirect.com/science/article/abs/pii/S0012821X99002216
  29. https://www.sciencedirect.com/science/article/abs/pii/S1387380616301075
  30. https://pubs.rsc.org/en/content/articlehtml/2025/ja/d4ja00301b
  31. https://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Sm152
  32. https://www.sciencedirect.com/science/article/abs/pii/S1387380602006656
  33. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/rcm.9912
  34. https://www-nds.iaea.org/publications/tecdocs/technical-reports-series-156.pdf
  35. https://opg.optica.org/abstract.cfm?uri=ao-17-6-856
  36. https://periodictable.com/Isotopes/062.148/index.html
  37. https://atom.kaeri.re.kr/cgi-bin/nuclide?nuc=Sm148
  38. https://www.chemlin.org/isotope/samarium-148
  39. https://adsabs.harvard.edu/full/1967ApJ...149..577M
  40. https://www.science.org/doi/10.1126/sciadv.adv3148
  41. http://www.lnhb.fr/nuclides/Sm-151_com.pdf
  42. https://www-nds.iaea.org/wimsd/fpyield.htm
  43. https://www-nds.iaea.org/sgnucdat/c2.htm
  44. https://www.nrc.gov/docs/ML0335/ML033510115.pdf
  45. http://www.lnhb.fr/nuclides/Sm-153_tables.pdf
  46. https://jnm.snmjournals.org/content/45/8/1358
  47. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/020570s008lbl.pdf
  48. https://jnm.snmjournals.org/content/jnumed/35/1/63.full.pdf
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