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mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/isotope">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48249"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/The-discovery-of-isotopes">The discovery of isotopes</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48250"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/The-discovery-of-isotopes#ref48250">Nuclear stability</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48251"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/The-discovery-of-isotopes#ref48251">Radioactive isotopes</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48252"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/Elemental-and-isotopic-abundances">Elemental and isotopic abundances</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48253"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances">Variations in isotopic abundances</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref48254"><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances#ref48254">Radioactive decay</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48255"><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances#ref48255">Mass fractionation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48256"><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances#ref48256">Other causes of isotopic abundance variations</a></li></ul></div></li><li data-target="#ref48257"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances#ref48257">Physical properties associated with isotopes</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48258"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/isotope/Variations-in-isotopic-abundances#ref48258">Effect of isotopes on atomic and molecular spectra</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref48259"><a class="w-100 link-gray-900" href="/science/isotope/Molecular-vibrations">Molecular vibrations</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48260"><a class="w-100 link-gray-900" href="/science/isotope/Molecular-vibrations#ref48260">Importance in the study of polyatomic molecules</a></li></ul></div></li><li data-target="#ref48261"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/Molecular-vibrations#ref48261">Chemical effects of isotopic substitution</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48262"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/isotope/Molecular-vibrations#ref48262">Effect of isotopic substitution on reaction rates</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref48263"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment">Isotope separation and enrichment</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref48264"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48264">Mass spectrometry</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48265"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48265">Distillation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48266"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48266">Chemical exchange reactions</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48267"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48267">Gaseous diffusion</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48268"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48268">Gas centrifugation</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref48269"><a class="w-100 link-gray-900" href="/science/isotope/Isotope-separation-and-enrichment#ref48269">Photochemical enrichment methods</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900 selected" href="https://www.britannica.com/science/isotope/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/isotope">Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" href="https://www.britannica.com/science/isotope/images-videos">Images & Videos</a> <div class="slider js-slider position-relative d-inline-flex align-items-center mw-100 "> <div class="slider-container js-slider-container overflow-hidden d-flex overflow-hidden text-nowrap ml-15"> <a href="/video/What-are-isotopes/246891" data-href="/media/1/296583/246891" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/64/216564-138-51A467D7/What-are-isotopes.jpg?w=400&h=225&c=crop" alt="What are 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</span> <span class="breadcrumb-item "> <a class="link-gray-600" href="/browse/Chemistry">Chemistry</a> </span> </nav> <h1 class="mb-5">isotope: References & Edit History</h1> <div class="border-bottom mt-20"></div> <div id="More-Articles"> <h2 class="my-20">More Articles On This Topic</h2> <div class="mb-30"> <section><h3>Assorted References</h3><ul class="list-unstyled"></ul><ul class="list-unstyled"><li><strong>meteorites</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/meteorite/The-ages-of-meteorites-and-their-components#ref1140105" class="md-crosslink " data-show-preview="true">meteorite: Cosmic-ray exposure ages of meteorites</a></span></li></ul></li></ul></section><section><h3>applications</h3><ul class="list-unstyled"></ul><ul class="list-unstyled"><li><strong>absolute dating</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/dating-geochronology/Principles-of-isotopic-dating#ref584871" class="md-crosslink " data-show-preview="true">dating: Principles of isotopic dating</a></span></li></ul></li><li><strong>centrifugation</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/technology/centrifuge/Vacuum-type-centrifuges#ref68023" class="md-crosslink " data-show-preview="true">centrifuge: Vacuum-type centrifuges</a></span></li></ul></li><li><strong>climatic change and geochronology</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/Pleistocene-Epoch/Marine-oxygen-isotope-record#ref586154" class="md-crosslink " data-show-preview="true">Pleistocene Epoch: Marine oxygen isotope record</a></span></li></ul></li><li><strong>earth evolution studies</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/place/Earth/Accretion-of-the-early-Earth#ref843785" class="md-crosslink " data-show-preview="true">Earth: Accretion of the early Earth</a></span></li></ul></li><li><strong>mass spectrometry</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/mass-spectrometry/Important-technical-adjuncts#ref619965" class="md-crosslink " data-show-preview="true">mass spectrometry: Atomic masses</a></span></li></ul></li><li><strong>metabolism</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/metabolism/The-study-of-metabolic-pathways#ref507589" class="md-crosslink " data-show-preview="true">metabolism: The study of metabolic pathways</a></span></li></ul></li><li><strong>nuclear fission</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/nuclear-fission/Fission-decay-chains-and-charge-distribution#ref496480" class="md-crosslink " data-show-preview="true">nuclear fission: Fission decay chains and charge distribution</a></span></li></ul></li><li><strong>resonance-ionization mass spectrometry</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/spectroscopy/Lasers-for-RIS#ref620620" class="md-crosslink " data-show-preview="true">spectroscopy: Resonance-ionization mass spectrometry</a></span></li></ul></li></ul></section><section><h3>chemical elements</h3><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/chemical-element/The-atomic-nature-of-the-elements#ref622227" class="md-crosslink " data-show-preview="true">chemical element: The existence of isotopes</a></span></li></ul><ul class="list-unstyled"><li><strong>actinoid elements</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/actinoid-element#ref622100" class="md-crosslink " data-show-preview="true">actinoid element: General similarities of the actinoid elements</a></span></li></ul></li><li><strong>helium</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/helium-chemical-element#ref1076820" class="md-crosslink " data-show-preview="true">helium: Abundance and isotopes</a></span></li></ul></li><li><strong>hydrogen</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/hydrogen/Isotopes-of-hydrogen#ref621361" class="md-crosslink " data-show-preview="true">hydrogen: Isotopes of hydrogen</a></span></li></ul></li><li><strong>lead</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/lead-chemical-element/Properties-of-the-element#ref290755" class="md-crosslink " data-show-preview="true">lead: Nuclear properties</a></span></li></ul></li><li><strong>nitrogen</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/nitrogen/Biological-and-physiological-significance#ref1063049" class="md-crosslink " data-show-preview="true">nitrogen: Isotopes of nitrogen</a></span></li></ul></li><li><strong>oxygen group elements</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/oxygen-group-element/Isotopes#ref621757" class="md-crosslink " data-show-preview="true">oxygen group element: Isotopes</a></span></li></ul></li><li><strong>rare-earth elements</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/rare-earth-element/Abundance-occurrence-and-reserves#ref622041" class="md-crosslink " data-show-preview="true">rare-earth element: Abundance, occurrence, and reserves</a></span></li><li> <span class="index-xref">In <a href="https://www.britannica.com/science/rare-earth-element/Nuclear-properties#ref1177503" class="md-crosslink " data-show-preview="true">rare-earth element: Nuclear properties</a></span></li></ul></li><li><strong>silver</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/silver#ref55290" class="md-crosslink " data-show-preview="true">silver: Properties, uses, and occurrence</a></span></li></ul></li><li><strong>transuranium elements</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/transuranium-element#ref622149" class="md-crosslink " data-show-preview="true">transuranium element: Discovery of the first transuranium elements</a></span></li></ul></li></ul></section><section><h3>structure and properties</h3><ul class="list-unstyled"></ul><ul class="list-unstyled"><li><strong>atomic nucleus</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/atom/Atomic-mass-and-isotopes#ref496539" class="md-crosslink " data-show-preview="true">atom: Atomic mass and isotopes</a></span></li></ul></li><li><strong>atomic weight</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/atomic-weight#ref189874" class="md-crosslink " data-show-preview="true">atomic weight</a></span></li></ul></li><li><strong>beta decay</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/beta-decay#ref894367" class="md-crosslink " data-show-preview="true">beta decay</a></span></li></ul></li><li><strong>geochemistry</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/geology/Isotopic-geochemistry#ref148749" class="md-crosslink " data-show-preview="true">geology: Isotopic geochemistry</a></span></li></ul></li><li><strong>mass spectrometry</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/mass-spectrometry#ref619852" class="md-crosslink " data-show-preview="true">mass spectrometry: History</a></span></li></ul></li><li><strong>Mossbauer effect</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/Mossbauer-effect#ref661063" class="md-crosslink " data-show-preview="true">Mössbauer effect: Isotope suitability</a></span></li></ul></li><li><strong>periodic system</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/periodic-table/The-first-periodic-table#ref621302" class="md-crosslink " data-show-preview="true">periodic table: Significance of atomic numbers</a></span></li></ul></li><li><strong>spectroscopy</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/science/spectroscopy#ref620030" class="md-crosslink " data-show-preview="true">spectroscopy</a></span></li></ul></li></ul></section><section><h3>work of</h3><ul class="list-unstyled"></ul><ul class="list-unstyled"><li><strong>Aston</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/biography/Francis-William-Aston#ref1088083" class="md-crosslink " data-show-preview="true">Francis William Aston</a></span></li></ul></li><li><strong>Richards</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/biography/Theodore-William-Richards#ref619484" class="md-crosslink " data-show-preview="true">Theodore William Richards</a></span></li></ul></li><li><strong>Soddy</strong><ul class="list-unstyled"><li> <span class="index-xref">In <a href="https://www.britannica.com/biography/Frederick-Soddy#ref204460" class="md-crosslink " data-show-preview="true">Frederick Soddy</a></span></li></ul></li></ul></section></div> </div> <div id="Additional-Reading"> <div class="border-top"><h2 class="my-20">Additional Reading</h2> </div><div class="mb-30"> <span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph">Useful sources include <span class="text-smallcaps">F.W. Aston</span>, <em>Mass Spectra and Isotopes</em>, 2nd ed. (1942), a history of the discovery of radioactive and stable isotopes; <span class="text-smallcaps">Gerhart Friedlander</span> et al., <em>Nuclear and Radiochemistry</em>, 3rd ed. (1981); <span class="text-smallcaps">Michael J. Pilling</span> and <span class="text-smallcaps">Paul W. Seakins</span>, <em>Reaction Kinetics</em> (1995); <span class="text-smallcaps">Stelio Villani</span>, <em>Isotope Separation</em>, trans. from Italian (1967); and <span class="text-smallcaps">James W. Truran</span>, “Nucleosynthesis,” <em>Annual Review of Nuclear and Particle Science</em>, 34:53–97 (1984).</p><span class="marker MOD1 mod-inline"></span> <span class="md-signature"><a href="/contributor/Gregory-F-Herzog/3392">Gregory F. Herzog</a></span></div> </div> <div id="contributors" class="pt-20 mt-30 border-top"> <div id="contributors-isotope"> <h2 class="mb-20">Article Contributors</h2> <h3 class="topic-contributors-subtitle h4">Primary Contributors</h3> <ul class="list-unstyled mt-10 mb-20 contributor-PRIMARY"> <li> <a href="/contributor/Gregory-F-Herzog/3392">Gregory F. Herzog</a> <div class="font-serif my-10">Professor of Chemistry, Rutgers University, New Brunswick, New Jersey.</div> </li> </ul> <h3 class="topic-contributors-subtitle h4">Other Encyclopedia Britannica Contributors</h3> <ul class="list-unstyled mt-10 mb-20 contributor-NON_PRIMARY_EB"> <li> <a href="/editor/Barbara-A-Schreiber/6493">Barbara A. Schreiber</a> </li> <li> <a href="/editor/Yamini-Chauhan/7697573">Yamini Chauhan</a> </li> <li> <a href="/editor/Aakanksha-Gaur/9336039">Aakanksha Gaur</a> </li> <li> <a href="/editor/Erik-Gregersen/6723">Erik Gregersen</a> </li> <li> <a href="/editor/William-L-Hosch/6481">William L. Hosch</a> </li> <li> <a href="/editor/Gita-Liesangthem/7666593">Gita Liesangthem</a> </li> <li> <a href="/editor/Gloria-Lotha/7666594">Gloria Lotha</a> </li> <li> <a href="/editor/Kokila-Manchanda/7666591">Kokila Manchanda</a> </li> <li> <a href="/editor/Emily-Rodriguez/9852325">Emily Rodriguez</a> </li> <li> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a> </li> <li> <a href="/editor/Grace-Young/7666614">Grace Young</a> </li> <li> <a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a> </li> </ul> </div> </div> <div id="history" class="pt-20 border-top"> <div id="history-isotope"> <h2 class="mb-20">Article History</h2> <div class="mw-100 overflow-scroll"> <table class="article-history table"> <thead> <tr> <th class="topic-history-type">Type</th> <th class="topic-history-description">Description</th> <th class="topic-history-contributor">Contributor</th> <th class="topic-history-date">Date</th> </tr> </thead> <tbody> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: National Isotope Development Center - Isotope Basics.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Emily-Rodriguez/9852325">Emily Rodriguez</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Nov 21, 2024</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: The University of Western Australia - Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Yamini-Chauhan/7697573">Yamini Chauhan</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Sep 26, 2024</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Michigan State University - MSUToday - What is an isotope?</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Grace-Young/7666614">Grace Young</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jul 18, 2024</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Open Library Publishing Platform - Isotopes of the elements.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Gloria-Lotha/7666594">Gloria Lotha</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jan 16, 2024</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: UEN Digital Press with Pressbooks - Introductory Chemistry - Use of Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Emily-Rodriguez/9852325">Emily Rodriguez</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Dec 08, 2023</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: International Atomic Energy Agency - What are Isotopes?</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Emily-Rodriguez/9852325">Emily Rodriguez</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Oct 12, 2023</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Chemistry LibreTexts - Isotope.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Gloria-Lotha/7666594">Gloria Lotha</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Oct 20, 2022</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Energy Education - Isotope.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Emily-Rodriguez/9852325">Emily Rodriguez</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Apr 26, 2022</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> Top Questions updated.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Oct 22, 2021</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Cool Kid Facts - Isotope.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Gloria-Lotha/7666594">Gloria Lotha</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jan 18, 2021</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> New media added.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Barbara-A-Schreiber/6493">Barbara A. Schreiber</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 02, 2020</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> Media added.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Apr 09, 2020</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Add new Web site: Chemicool Dictionary - Definition of Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Aakanksha-Gaur/9336039">Aakanksha Gaur</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Feb 15, 2019</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> <span class="topic-history-diff-link link-blue" data-diff="/12/110412-008">Changed "element 118" to "oganesson."</span></td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Erik-Gregersen/6723">Erik Gregersen</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Dec 12, 2016</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> <span class="topic-history-diff-link link-blue" data-diff="/12/110412-007">Definition of cosmic rays modified to include electrons.</span></td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Erik-Gregersen/6723">Erik Gregersen</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Oct 04, 2010</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: Buzzle.com - Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: World Nuclear Association - Radioisotopes in Medicine.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: Rader's Chem4Kids.com - Isotope.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: University of Georgia - Isotope.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: USGS - Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: University of Colorado at Boulder - Isotopes.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: USGS - Understanding Our Planet Through Chemistry - Elements, Isotopes, and Radioactivity.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Veenu-Setia/7666606">Veenu Setia</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Jun 11, 2008</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="link"></em> </td> <td> Added new Web site: Understanding Our Planet Through Chemistry - Elements, isotopes, and radioactivity.</td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/Kokila-Manchanda/7666591">Kokila Manchanda</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Apr 23, 2007</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> <span class="topic-history-diff-link link-blue" data-diff="/12/110412-004">Article revised and updated.</span></td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/William-L-Hosch/6481">William L. Hosch</a></li> </ul> </td> <td data-type="date" class="text-nowrap"> Mar 16, 2007</td> </tr> <tr> <td class="history-type"> <em class="material-icons " data-icon="edit"></em> </td> <td> <span class="topic-history-diff-link link-blue" data-diff="/12/110412-004">Bibliography revised.</span></td> <td class="history-contributor"> <ul class="list-unstyled"> <li data-type="contributor"> <a href="/editor/William-L-Hosch/6481">William L. 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