Editing Samarium (section)

==Isotopes==
{{main|Isotopes of samarium}}
Naturally occurring samarium is composed of five stable [[isotope]]s: <sup>144</sup>Sm, <sup>149</sup>Sm, <sup>150</sup>Sm, <sup>152</sup>Sm and <sup>154</sup>Sm, and two extremely long-lived [[radioisotope]]s, [[samarium-147|<sup>147</sup>Sm]] (half-life ''t''<sub>1/2</sub>&nbsp;= 1.06{{e|11}} years) and <sup>148</sup>Sm (7{{e|15}} years), with <sup>152</sup>Sm being the most abundant ([[natural abundance|26.75%]]).{{NUBASE2020|ref}} <sup>149</sup>Sm is listed by various sources as being stable,{{NUBASE2020|ref}}<ref>{{Cite web |publisher=Brookhaven National Laboratory |title=Chart of the nuclides |url=http://www.nndc.bnl.gov/chart/reCenter.jsp?z=62&n=87 |access-date=2011-02-13 |archive-date=2017-07-29 |archive-url=https://web.archive.org/web/20170729181515/http://www.nndc.bnl.gov/chart/reCenter.jsp?z=62&n=87 |url-status=dead }}</ref> but some sources state that it is radioactive,<ref>Holden, Norman E. "Table of the isotopes" in {{RubberBible86th}}</ref> with a lower bound for its half-life given as {{val|2|e=15}} years.{{NUBASE2020|ref}} Some [[observationally stable]] samarium isotopes are predicted to decay to [[isotopes of neodymium]].<ref name="rare_decays">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |title=Experimental searches for rare alpha and beta decays |date=2019 |journal=[[European Physical Journal A]] |volume=55 |number=140 |pages=4–6 <!--data table-->|doi=10.1140/epja/i2019-12823-2 |arxiv=1908.11458 |bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref> The long-lived isotopes <sup>146</sup>Sm, <sup>147</sup>Sm, and <sup>148</sup>Sm undergo [[alpha decay]] to [[neodymium]] isotopes. Lighter unstable isotopes of samarium mainly decay by [[electron capture]] to [[promethium]], while heavier ones [[beta decay]] to [[europium]].{{NUBASE2020|ref}} The known isotopes range from <sup>129</sup>Sm to <sup>168</sup>Sm.{{NUBASE2020|ref}}<ref name=Ln922>{{cite journal |last1=Kiss |first1=G. G. |last2=Vitéz-Sveiczer |first2=A. |last3=Saito |first3=Y. |display-authors=et al. |title=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 |journal=The Astrophysical Journal |volume=936 |issue=107 |date=2022 |page=107 |doi=10.3847/1538-4357/ac80fc |bibcode=2022ApJ...936..107K |s2cid=252108123 |doi-access=free |hdl=2117/375253 |hdl-access=free }}</ref> The half-lives of <sup>151</sup>Sm and <sup>145</sup>Sm are 90 years and 340 days, respectively. All remaining [[radioisotopes]] have half-lives that are less than 2 days, and most these have half-life less than 48 seconds. Samarium also has twelve known [[nuclear isomer]]s, the most stable of which are <sup>141m</sup>Sm ([[half-life]] 22.6 minutes), <sup>143m1</sup>Sm (''t''<sub>1/2</sub>&nbsp;= 66 seconds), and <sup>139m</sup>Sm (''t''<sub>1/2</sub>&nbsp;= 10.7 seconds).{{NUBASE2020|ref}} Natural samarium has a [[Radioactive decay|radioactivity]] of 127&nbsp;[[becquerel|Bq]]/g, mostly due to <sup>147</sup>Sm,<ref name=iaea1512>{{cite report |url=https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1512_web.pdf |title=Radiation Protection and NORM Residue Management in the Production of Rare Earths from Thorium Containing Minerals |publisher=[[International Atomic Energy Agency]] |series=Safety Report Series |number=68 |date=2011 |page=174 |access-date=2022-07-25}}</ref> which [[alpha decay]]s to <sup>143</sup>Nd with a [[half-life]] of 1.06{{e|11}} years and is used in [[samarium–neodymium dating]].<ref name=DePaolo147Sm>{{cite journal|last1=Depaolo|first1=D. J.|last2=Wasserburg|first2=G. J.|title=Nd isotopic variations and petrogenetic models |journal=Geophysical Research Letters|volume=3|pages=249|year=1976|doi=10.1029/GL003i005p00249|bibcode=1976GeoRL...3..249D|issue=5|url=https://authors.library.caltech.edu/41937/1/grl330.pdf}}</ref><ref name=McCulloch147Sm>{{cite journal|last1=McCulloch|first1=M. T.|last2=Wasserburg|first2=G. J. |title=Sm-Nd and Rb-Sr Chronology of Continental Crust Formation |journal=Science |volume=200 |pages=1003–11 |year=1978 |doi=10.1126/science.200.4345.1003 |issue=4345 |pmid=17740673 |bibcode=1978Sci...200.1003M |s2cid=40675318 |url=https://resolver.caltech.edu/CaltechAUTHORS:20131107-143832294 }}</ref> <sup>146</sup>Sm is an [[extinct radionuclide]], with the half-life of 9.20{{e|7}} years.<ref name=Chiera2024/> There have been searches of samarium-146 as a [[primordial nuclide]], because its half-life is long enough such that minute quantities of the element should persist today.<ref>{{cite journal | last=Macfarlane | first=Ronald D. | title=Natural Occurrence of Samarium-146 | journal=Nature | volume=188 | issue=4757 | year=1960 | issn=0028-0836 | doi=10.1038/1881180a0 | pages=1180–1181| bibcode=1960Natur.188.1180M | s2cid=4217617 }}</ref> It can be used in radiometric dating.<ref>{{cite journal |title=Separation of samarium and neodymium: a prerequisite for getting signals from nuclear synthesis |author=Samir Maji |journal=Analyst |volume=131 |pages=1332–1334 |year=2006 |doi=10.1039/b608157f |pmid=17124541 |issue=12 |bibcode=2006Ana...131.1332M |display-authors=1 |last2=Lahiri |first2=Susanta |last3=Wierczinski |first3=Birgit |last4=Korschinek |first4=Gunther}}</ref>

Samarium-149 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]] <sup>149</sup>Nd (yield 1.0888%). <sup>149</sup>Sm is a decay product and [[neutron]]-absorber in [[nuclear reactor]]s, with a [[neutron poison]] effect that is second in importance for reactor design and operation only to [[Xenon-135|<sup>135</sup>Xe]].<ref>{{cite book|title=DOE Fundamentals Handbook: Nuclear Physics and Reactor Theory |date=January 1993 |publisher=[[U.S. Department of Energy]] |url=http://www.hss.energy.gov/nuclearsafety/ns/techstds/standard/hdbk1019/h1019v2.pdf |pages=34, 67 |archive-url=https://web.archive.org/web/20090322040810/http://www.hss.energy.gov/nuclearsafety/ns/techstds/standard/hdbk1019/h1019v2.pdf |archive-date=2009-03-22 }}</ref><ref>{{Cite web |last=K. |first=Khattab |date=2005 |title=Comparison of xenon-135 and samarium-149 poisoning in the Miniature Neutron Source Reactor |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:36069288 |language=Arabic}}</ref> Its [[neutron cross section]] is 41000 [[Barn (unit)|barn]]s for [[thermal neutron]]s.<ref>{{Cite conference |first1=Carlos E. |last1=Espinosa |first2=Bardo E.J. |last2=Bodmann |title=Modeling and simulation of nuclear fuel in scenarios with long time scales |url=https://inis.iaea.org/search/search.aspx?orig_q=RN:46133777 |conference=19. ENFIR: meeting on nuclear reactor physics and thermal hydraulics |language=English}}</ref> Because samarium-149 is not radioactive and is not removed by decay, it presents problems somewhat different from those encountered with xenon-135. The equilibrium concentration (and thus the poisoning effect) builds to an equilibrium value during reactor operations in about 500 hours (about three weeks), and since samarium-149 is stable, its concentration remains essentially constant during reactor operation.<ref>DOE Handbook, pp. 43–47.</ref>

[[File:153Sm-lexidronam structure.svg|thumb|Chemical structure of [[Samarium (153Sm) lexidronam|Sm-EDTMP]]|alt=Chemical structure of samarium (153Sm) lexidronam]]
Samarium-153 is a beta emitter with a half-life of 46.3 hours. It is used to kill cancer cells in [[lung cancer]], [[prostate cancer]], [[breast cancer]], and [[osteosarcoma]]. For this purpose, samarium-153 is [[Chelation|chelated]] with ethylene diamine tetramethylene phosphonate ([[EDTMP]]) and injected intravenously. The chelation prevents accumulation of radioactive samarium in the body that would result in excessive irradiation and generation of new cancer cells.<ref name="emsley" /> The corresponding drug has several names including [[samarium (153Sm) lexidronam|samarium (<sup>153</sup>Sm) lexidronam]]; its [[trade name]] is Quadramet.<ref>{{cite web|access-date=2009-06-06|url=http://www.centerwatch.com/patient/drugs/dru267.html|title=Centerwatch About drug Quadramet|archive-date=2008-10-09|archive-url=https://web.archive.org/web/20081009094258/http://www.centerwatch.com/patient/drugs/dru267.html}}</ref><ref>{{cite journal |last1=Pattison |first1=John E. |title=Finger doses received during 153Sm injections |journal=Health Physics |volume=77 |issue=5 |pages=530–5 |date=1999 |pmid=10524506 |doi=10.1097/00004032-199911000-00006|bibcode=1999HeaPh..77..530P }}</ref><ref>{{cite journal |last1=Finlay |first1=I. G. |last2=Mason |first2=M. D. |last3=Shelley |first3=M. |title=Radioisotopes for the palliation of metastatic bone cancer: a systematic review |journal=The Lancet Oncology |volume=6 |issue=6 |pages=392–400 |date=2005 |pmid=15925817 |doi=10.1016/S1470-2045(05)70206-0}}</ref>