View source for Physics: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 [[Physics:Stable isotope|stable isotope]]s of [[Chemistry:Chlorine|chlorine]], the other being chlorine-35 ({{SimpleNuclide|Chlorine|35}}). Its [[Physics:Atomic nucleus|nucleus]] contains 17 protons and 20 neutrons for a total of 37 [[Physics:Nucleon|nucleon]]s. Chlorine-37 accounts for 24.23% of natural chlorine, chlorine-35 accounting for 75.77%, giving chlorine [[Physics:Atom|atom]]s in bulk an apparent atomic weight of {{val|35.453|(2)|u=g/mol}}.<ref>{{AtWt 2005}}</ref>

Remarkably, solar neutrinos were discovered by an experiment using a radiochemical method based on chlorine-37 transmutation.<ref name="SciAm">
{{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}}</ref>

==Neutrino detection==
{{Main|Physics:Homestake experiment}}

One of the historically important radiochemical methods of solar [[Astronomy:Neutrino detector|neutrino detection]] is based on inverse [[Physics:Electron capture|electron capture]] triggered by the absorption of an [[Physics:Electron neutrino|electron neutrino]].<ref name="Sutton">
{{cite book|last=Sutton|first=Christine|title=Spaceship Neutrino|url=https://archive.org/details/spaceshipneutrin0000sutt|url-access=registration|quote=chlorine-37 neutrino.|publisher={{wipe|Cambridge University Press}}|pages=[https://archive.org/details/spaceshipneutrin0000sutt/page/151 151]–152|year=1992|isbn=978-0-521-36404-1|oclc=25246163}}</ref> Chlorine-37 transmutes into argon-37 via the reaction<ref>
{{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}}</ref>
:{{SimpleNuclide|Chlorine|37}} + {{Subatomic particle|Electron neutrino}} → {{SimpleNuclide|Argon|37}} + {{Subatomic particle|Electron-}}.

Argon-37 then de-excites itself via [[Physics:Electron capture|electron capture]] (half-life = 35&nbsp;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.<ref name="Sutton"/><ref>
{{cite journal|author=A.H. Snell, F. Pleasonton|title=Spectrometry of the Neutrino Recoils of Argon-37|journal=[[Physics:Physical Review|Physical Review]]|volume=100 |issue=5 |pages=1396–1403|year=1955|doi=10.1103/PhysRev.100.1396
|bibcode = 1955PhRv..100.1396S}}</ref> The detection of these electrons confirms that a neutrino event took place. Detection methods involve several hundred thousand liters of [[Chemistry:Carbon tetrachloride|carbon tetrachloride]] (CCl<sub>4</sub>) or [[Chemistry:Tetrachloroethylene|tetrachloroethylene]]<!--Also known as perchloroethylene, perchloroethene, perc, PCE --> (C<sub>2</sub>Cl<sub>4</sub>) stored in underground tanks.<ref name="SciAm"/><ref name="Sutton"/><ref>{{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=[[Company:World Scientific|World Scientific]]|pages=87–89|year=2005|isbn=978-981-238-244-3}}</ref>

==Occurrence==
The representative terrestrial abundance of chlorine-37 is 24.22(4)% of chlorine atoms,<ref name="TICE">{{AtWt TICE 1997}}</ref> 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<ref name="2000Rev">{{AtWt Rev 2000}}</ref>

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 sea water, although the isotopic composition of [[Chemistry:Organochlorine compound|organochlorine compound]]s can vary in either direction from the SMOC standard in the range of several [[Parts per thousand|parts per thousand]].<ref name="2000Rev" />

==See also==
*[[Physics:Beta decay|Beta decay]]
*Neutrino detection
*Isotopic tracer
*[[Physics:Isotopes of chlorine|Isotopes of chlorine]]

==References==
{{Reflist|2}}

[[Category:Isotopes of chlorine]]

{{Sourceattribution|Chlorine-37}}