{"id":93,"date":"2026-04-10T02:53:01","date_gmt":"2026-04-10T02:53:01","guid":{"rendered":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/ch029-xhtml\/"},"modified":"2026-05-07T20:28:48","modified_gmt":"2026-05-07T20:28:48","slug":"4-1-background-and-historical-development","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/4-1-background-and-historical-development\/","title":{"raw":"4.1 Background and Historical Development","rendered":"4.1 Background and Historical Development"},"content":{"raw":"
\r\n
\r\n\r\nTolstikhin and Kamensky (1969) first reported on the concept of using the [latex]\\frac{_{}^{3}H}{_{}^{3}{He}}[\/latex] parent\u2011child concentrations to determine an age of water. The method was used to investigate circulation of ocean waters (Jenkins & Clarke, 1976) and later applied to lakes (Torgerson et al., 1979). About a decade later, the first use of tritium\u2011helium age dating for groundwater was reported by Schlosser and others (1988) and Poreda and others (1988).\r\n\r\n<\/div>\r\n
\r\n\r\nHelium has two naturally occurring and stable isotopes. Most natural [latex]He[\/latex] is [latex]_{}^{4}{He}[\/latex] with an abundance that is nearly a million times greater than[latex]_{}^{3}{He}[\/latex] in the atmosphere. The [latex]_{}^{3}{He}[\/latex] found in groundwater can be derived from the following:\r\n\r\n<\/div>\r\n
    \r\n \t
  1. the atmosphere,<\/li>\r\n \t
  2. subsurface production in the Earth\u2019s crust,<\/li>\r\n \t
  3. primordial [latex]He[\/latex] (e.g., degassing from mantle rocks), or<\/li>\r\n \t
  4. the decay of [latex]_{}^{3}H[\/latex].<\/li>\r\n<\/ol>\r\n
    \r\n\r\nThe [latex]He[\/latex] isotopic composition of each of these sources is vastly different. The atmosphere contains about 5.24\u00a0ppmv (ppm volume) [latex]He[\/latex] with a [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex]\u00a0ratio of 1.382\u00a0\u00b1\u00a00.005x10-6<\/sup> (Sano et al., 2013). In the subsurface, [latex]_{}^{4}{He}[\/latex] is a radioactive decay product of [latex]U[\/latex] and [latex]Th[\/latex] and a small amount of [latex]_{}^{3}{He}[\/latex] is produced from the fission of [latex]_{}^{6}{Li},[\/latex] which produces [latex]_{}^{3}H[\/latex] that then decays to [latex]_{}^{3}{He}[\/latex].\r\n\r\n<\/div>\r\n
    \r\n\r\nThe [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex] ratio produced by the Earth\u2019s crust ranges from about 10\u20118<\/sup> to 10\u20117<\/sup> and depends on many factors including neutron production and the [latex]Li[\/latex] content of crustal rocks (Solomon, 2000). Primordial [latex]He[\/latex] that degasses from the mantle is relatively rich in [latex]_{}^{3}{He}[\/latex] with a [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex] ratio that ranges from about 1x10\u20135<\/sup> to 2x10\u20135<\/sup> . When produced from [latex]_{}^{3}H[\/latex] decay, [latex]_{}^{3}{He}[\/latex] is called [latex]_{}^{3}{He}_{trit}[\/latex] and is used for [latex]\\frac{_{}^{3}H}{_{}^{3}{He}}[\/latex] dating. As is discussed later in this section, separating [latex]_{}^{3}{He}_{trit}[\/latex] from other components is an essential task for dating.\r\n\r\n<\/div>\r\n<\/div>","rendered":"
    \n
    \n

    Tolstikhin and Kamensky (1969) first reported on the concept of using the [latex]\\frac{_{}^{3}H}{_{}^{3}{He}}[\/latex] parent\u2011child concentrations to determine an age of water. The method was used to investigate circulation of ocean waters (Jenkins & Clarke, 1976) and later applied to lakes (Torgerson et al., 1979). About a decade later, the first use of tritium\u2011helium age dating for groundwater was reported by Schlosser and others (1988) and Poreda and others (1988).<\/p>\n<\/div>\n

    \n

    Helium has two naturally occurring and stable isotopes. Most natural [latex]He[\/latex] is [latex]_{}^{4}{He}[\/latex] with an abundance that is nearly a million times greater than[latex]_{}^{3}{He}[\/latex] in the atmosphere. The [latex]_{}^{3}{He}[\/latex] found in groundwater can be derived from the following:<\/p>\n<\/div>\n

      \n
    1. the atmosphere,<\/li>\n
    2. subsurface production in the Earth\u2019s crust,<\/li>\n
    3. primordial [latex]He[\/latex] (e.g., degassing from mantle rocks), or<\/li>\n
    4. the decay of [latex]_{}^{3}H[\/latex].<\/li>\n<\/ol>\n
      \n

      The [latex]He[\/latex] isotopic composition of each of these sources is vastly different. The atmosphere contains about 5.24\u00a0ppmv (ppm volume) [latex]He[\/latex] with a [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex]\u00a0ratio of 1.382\u00a0\u00b1\u00a00.005×10-6<\/sup> (Sano et al., 2013). In the subsurface, [latex]_{}^{4}{He}[\/latex] is a radioactive decay product of [latex]U[\/latex] and [latex]Th[\/latex] and a small amount of [latex]_{}^{3}{He}[\/latex] is produced from the fission of [latex]_{}^{6}{Li},[\/latex] which produces [latex]_{}^{3}H[\/latex] that then decays to [latex]_{}^{3}{He}[\/latex].<\/p>\n<\/div>\n

      \n

      The [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex] ratio produced by the Earth\u2019s crust ranges from about 10\u20118<\/sup> to 10\u20117<\/sup> and depends on many factors including neutron production and the [latex]Li[\/latex] content of crustal rocks (Solomon, 2000). Primordial [latex]He[\/latex] that degasses from the mantle is relatively rich in [latex]_{}^{3}{He}[\/latex] with a [latex]\\frac{_{}^{3}{He}}{_{}^{4}{He}}[\/latex] ratio that ranges from about 1×10\u20135<\/sup> to 2×10\u20135<\/sup> . When produced from [latex]_{}^{3}H[\/latex] decay, [latex]_{}^{3}{He}[\/latex] is called [latex]_{}^{3}{He}_{trit}[\/latex] and is used for [latex]\\frac{_{}^{3}H}{_{}^{3}{He}}[\/latex] dating. As is discussed later in this section, separating [latex]_{}^{3}{He}_{trit}[\/latex] from other components is an essential task for dating.<\/p>\n<\/div>\n<\/div>\n","protected":false},"author":7,"menu_order":15,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-93","chapter","type-chapter","status-publish","hentry"],"part":30,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/93","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/users\/7"}],"version-history":[{"count":1,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/93\/revisions"}],"predecessor-version":[{"id":238,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/93\/revisions\/238"}],"part":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/parts\/30"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/93\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/media?parent=93"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapter-type?post=93"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/contributor?post=93"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/license?post=93"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}