Chlorine-37
{{Short description|Isotope of chlorine}}
{{Infobox isotope
|num_neutrons = 20
|num_protons = 17
|alternate_names =
|mass_number=37
|abundance = 24.23%
|symbol=Cl
|decay_product = None
|halflife=
|error_halflife =
|mass=36.965903
|excess_energy =
|binding_energy =
|spin =
|decay_mode1=
|decay_energy1=
}}
Chlorine-37 ({{SimpleNuclide|Chlorine|37}}), is one of the stable isotopes of chlorine, the other being chlorine-35 ({{SimpleNuclide|Chlorine|35}}). Its nucleus contains 17 protons and 20 neutrons for a total of 37 nucleons. Chlorine-37 accounts for 24.23% of natural chlorine, chlorine-35 accounting for 75.77%, giving chlorine atoms in bulk an apparent atomic weight of {{val|35.45|(1)|u=g/mol}}.{{Citation |last=Prohaska |first=Thomas |title=Standard atomic weights of the elements 2021 (IUPAC Technical Report) |date=2022-05-25 |work=Pure and Applied Chemistry |volume=94 |issue=5 |pages=573–600 |url=https://www.degruyter.com/document/doi/10.1515/pac-2019-0603/html |access-date=2024-06-07 |language=en |doi=10.1515/pac-2019-0603 |issn=0033-4545 |last2=Irrgeher |first2=Johanna |last3=Benefield |first3=Jacqueline |last4=Böhlke |first4=John K. |last5=Chesson |first5=Lesley A. |last6=Coplen |first6=Tyler B. |last7=Ding |first7=Tiping |last8=Dunn |first8=Philip J. H. |last9=Gröning |first9=Manfred |doi-access=free |display-authors=1}}
Remarkably, solar neutrinos were discovered by an experiment (Homestake Experiment) using a radiochemical method based on chlorine-37 transmutation.
{{cite journal|doi=10.1038/scientificamerican0769-28|author=J.N. Bahcall|title=Neutrinos from the Sun|url=http://www.sns.ias.edu/~jnb/Papers/Popular/Scientificamerican69/scientificamerican69.html|journal = Scientific American|volume = 221 |issue = 1 |year = 1969|pages=28–37|bibcode=1969SciAm.221a..28B}}
Neutrino detection
{{Main|Homestake experiment}}
One of the historically important radiochemical methods of solar neutrino detection is based on inverse electron capture triggered by the absorption of an electron neutrino.
{{cite book|last=Sutton|first=Christine|title=Spaceship Neutrino|url=https://archive.org/details/spaceshipneutrin0000sutt|url-access=registration|quote=chlorine-37 neutrino.|publisher=Cambridge University Press|pages=[https://archive.org/details/spaceshipneutrin0000sutt/page/151 151]–152|year=1992|isbn=978-0-521-36404-1|oclc=25246163}} Chlorine-37 transmutes into argon-37 via the reaction
{{cite book|author=F.H. Shu|title=The Physical Universe: An Introduction to Astronomy|url=https://archive.org/details/physicaluniverse00shuf|url-access=registration|quote=chlorine 37 neutrino.|publisher=University Science Books|page=[https://archive.org/details/physicaluniverse00shuf/page/n145 122]|year=1982|isbn=978-0-935702-05-7}}
:{{SimpleNuclide|Chlorine|37}} + {{Subatomic particle|Electron neutrino}} → {{SimpleNuclide|Argon|37}} + {{Subatomic particle|Electron-}}.
Argon-37 then decays via electron capture (half-life 35 d) into chlorine-37 via the reaction
:{{SimpleNuclide|Argon|37}} + {{Subatomic particle|Electron-}} → {{SimpleNuclide|Chlorine|37}} + {{Subatomic particle|Electron neutrino}}.
These last reactions involve Auger electrons of specific energies.
{{cite journal|author=A.H. Snell, F. Pleasonton|title=Spectrometry of the Neutrino Recoils of Argon-37|journal=Physical Review|volume=100 |issue=5 |pages=1396–1403|year=1955|doi=10.1103/PhysRev.100.1396
|bibcode = 1955PhRv..100.1396S}} The detection of these electrons confirms that a neutrino event occurred. Detection methods involve several hundred thousand liters of carbon tetrachloride (CCl4) or tetrachloroethylene (C2Cl4) stored in underground tanks.{{cite book|author = A. Bhatnagar, W. Livingston|title = Fundamental of Solar Astronomy|url = https://books.google.com/books?id=fe7XDuxCYjcC&dq=chlorine+37+neutrino&pg=PA88|publisher=World Scientific|pages=87–89|year=2005|isbn=978-981-238-244-3}}
Occurrence
The representative terrestrial abundance of chlorine-37 is 24.22(4)% of chlorine atoms,{{AtWt TICE 1997}} with a normal range of 24.14–24.36% of chlorine atoms. When measuring deviations in isotopic composition, the usual reference point is "Standard Mean Ocean Chloride" (SMOC), although a NIST Standard Reference Material (975a) also exists. SMOC is known to be around 24.219% chlorine-37 and to have an atomic weight of around 35.4525.{{AtWt Rev 2000}}
There is a known variation in the isotopic abundance of chlorine-37. This heavier isotope tends to be more prevalent in chloride minerals than in aqueous solutions such as seawater, although the isotopic composition of organochlorine compounds can vary in either direction from the SMOC standard in the range of several parts per thousand.
See also
References
{{Reflist|2}}