Samarium-147
{{Short description|Isotope of samarium}}
{{Infobox isotope
| name = Samarium-147
| image =
| image_caption =
| alternate_names =
| mass_number = 147
| symbol = Sm
| num_neutrons = 85
| num_protons = 62
| abundance = 15.00%
| halflife = 1.06{{e|11}} years
| decay_product = Neodymium-143
| decay_mass = 143
| decay_symbol = Nd
| parent = Promethium-147
| parent_mass = 147
| parent_symbol = Pm
| parent_decay = β−
| parent2 = Gadolinium-151
| parent2_mass = 151
| parent2_symbol = Gd
| parent2_decay = α
| parent3 =
| parent3_mass =
| parent3_symbol =
| parent3_decay =
| mass = 146.9148979(26)
| spin = 7/2−
| excess_energy =
| binding_energy =
| decay_mode1 = α
| decay_energy1 = 2.3113{{AME2020 II|ref}}
| decay_mode2 =
| decay_energy2 =
| decay_mode3 =
| decay_energy3 =
| decay_mode4 =
| decay_energy4 =
}}
Samarium-147 (147Sm or Sm-147) is an isotope of samarium, making up 15% of natural samarium. It is an extremely long-lived radioisotope, with a half-life of {{val|1.06|e=11}} years, although measurements have ranged from {{val|1.05|e=11}} to {{val|1.17|e=11}} years.{{Cite journal |last1=Wright |first1=P. M. |last2=Steinberg |first2=E. P. |last3=Glendenin |first3=L. E. |date=1961-07-01 |title=Half-Life of Samarium-147 |url=https://link.aps.org/doi/10.1103/PhysRev.123.205 |journal=Physical Review |volume=123 |issue=1 |pages=205–208 |doi=10.1103/PhysRev.123.205|bibcode=1961PhRv..123..205W }}{{Cite journal |last1=Kinoshita |first1=Norikazu |last2=Yokoyama |first2=Akihiko |last3=Nakanishi |first3=Takashi |date=2003 |title=Half-Life of Samarium-147 |url=https://www.jstage.jst.go.jp/article/jnrs2000/4/1/4_1_5/_article/-char/ja/ |journal=Journal of Nuclear and Radiochemical Sciences |volume=4 |issue=1 |pages=5–7 |doi=10.14494/jnrs2000.4.5|s2cid=120606011 |doi-access=free }} It is mainly used in radiometric dating.{{Cite book |url=https://pubs.acs.org/doi/book/10.1021/bk-1982-0176 |title=Nuclear and Chemical Dating Techniques: Interpreting the Environmental Record |date=1982-01-29 |publisher=AMERICAN CHEMICAL SOCIETY |isbn=978-0-8412-0669-4 |editor-last=Currie |editor-first=Lloyd A. |series=ACS Symposium Series |volume=176 |location=WASHINGTON, D. C. |language=en |doi=10.1021/bk-1982-0176.ch001}}
Uses
{{Main article|Samarium–neodymium dating}}
Samarium-147 is used in samarium–neodymium dating. The method of isochron dating is used to find the date at which a rock (or group of rocks) are formed.{{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}} The Sm-Nd isochron plots the ratio of radiogenic 143Nd to non-radiogenic 144Nd against the ratio of the parent isotope 147Sm to the non-radiogenic isotope 144Nd. 144Nd is used to normalize the radiogenic isotope in the isochron because it is a slightly radioactive and relatively abundant neodymium isotope.
The Sm-Nd isochron is defined by the following equation:
:
where:
: t is the age of the sample,
: λ is the decay constant of 147Sm,
: (eλt−1) is the slope of the isochron which defines the age of the system.
Alternatively, one can assume that the material formed from mantle material which was following the same path of evolution of these ratios as chondrites, and then again the time of formation can be calculated (see Samarium–neodymium dating#The CHUR model).{{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 }}
See also
References
{{reflist}}
{{Isotope sequence
|element=samarium
|lighter=samarium-146
|heavier=samarium-148
|before=gadolinium-151 (α)
promethium-147 (β−)
|after=neodymium-143 (α)
}}