Isotope - Separation, Enrichment, Radioactive

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Each method is based on some difference—sometimes a very slight one—between the physical or chemical properties of the isotopes of an element. Although the instrumentation normally serves analytical purposes, when suitably modified a mass spectrometer can also be used on a larger scale to prepare a purified sample of virtually any isotope. 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border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/isotope">isotope</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc 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" 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 isotopes and how do they work?" class="col-100" /> <div class="btn btn-sm btn-white btn-circle 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They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2025-01-18T00:00:00CST" >Jan 18, 2025</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/isotope/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn btn-sm border-2 btn-outline-red-400 border-red-400 module-spacing js-inline-ai-ask-button p-10 ml-5"> Ask the Chatbot </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Francis-William-Aston" topicid="39838">Francis William Aston</a></dd> <dd><a href="/biography/Frederick-Soddy" topicid="552022">Frederick Soddy</a></dd> <dd><a href="/biography/Theodore-William-Richards" topicid="502620">Theodore William Richards</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/deuterium" topicid="159684">deuterium</a></dd> <dd><a href="/science/radioactive-isotope" topicid="489027">radioactive isotope</a></dd> <dd><a href="/science/tritium" topicid="606002">tritium</a></dd> <dd><a href="/science/tantalum-181" topicid="2152678">tantalum-181</a></dd> <dd><a href="/science/tantalum-180" topicid="2152679">tantalum-180</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/isotope"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><span class="marker h11"></span><section data-level="1" id="ref48263"> <span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph">Most elements are found as mixtures of several isotopes. For certain applications in industry, medicine, and <a href="https://www.britannica.com/science/science" class="md-crosslink autoxref " data-show-preview="true">science</a>, samples enriched in one particular isotope are needed. Many methods have therefore been developed to separate the isotopes of an element from one another. Each method is based on some difference—sometimes a very slight one—between the physical or chemical properties of the isotopes of an element.</p><span class="marker MOD1 mod-inline"></span> <section data-level="2" id="ref48264"><h2 class="h2"><span id="ref496341"></span><a href="https://www.britannica.com/science/mass-spectrometry" class="md-crosslink " data-show-preview="true">Mass spectrometry</a></h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Although the instrumentation normally serves <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analytical" href="https://www.merriam-webster.com/dictionary/analytical" data-type="MW">analytical</a> purposes, when suitably modified a mass spectrometer can also be used on a larger scale to prepare a purified sample of virtually any isotope. Uranium-235 for the first <a href="https://www.britannica.com/technology/atomic-bomb" class="md-crosslink " data-show-preview="true">atomic bomb</a> was separated with specially built mass spectrometers. Because of its high operational costs, this method is ordinarily restricted to the production of a few milligrams to a few grams of various stable isotopes for scientific investigation.</p><span class="marker MOD2 mod-inline"></span></section> <section data-level="2" id="ref48265"><h2 class="h2"><span id="ref496342"></span><a href="https://www.britannica.com/science/distillation" class="md-crosslink " data-show-preview="true">Distillation</a></h2> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">The same factors that lead to the enrichment of <a href="https://www.britannica.com/science/alcohol" class="md-crosslink " data-show-preview="true">alcohol</a> in the vapour above a solution of water and alcohol permit the enrichment of isotopes. At temperatures below 220 °C (428 °F), for example, light water (<sup>1</sup><sub>1</sub><a href="https://www.britannica.com/science/hydrogen" class="md-crosslink autoxref " data-show-preview="true">H</a><sub>2</sub>O) vaporizes to a slightly greater extent than <a href="https://www.britannica.com/science/heavy-water" class="md-crosslink " data-show-preview="true">heavy water</a> (<sup>2</sup><sub>1</sub>H<sub>2</sub><a href="https://www.britannica.com/science/oxygen" class="md-crosslink autoxref " data-show-preview="true">O</a>, or D<sub>2</sub>O). The distillation of normal water, which contains both molecules, produces a vapour slightly enriched in <sup>1</sup><sub>1</sub>H<sub>2</sub>O. The residual liquid retains a correspondingly <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="enhanced" href="https://www.merriam-webster.com/dictionary/enhanced" data-type="MW">enhanced</a> concentration of heavy water. It is usually, though not always, true that the molecule with the lighter isotope will be more volatile. Similarly, distillation of liquefied <a href="https://www.britannica.com/science/carbon-monoxide" class="md-crosslink " data-show-preview="true">carbon monoxide</a> through several kilometres of piping yields a residue enriched in the heavier of <a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink autoxref " data-show-preview="true">carbon’s</a> two stable isotopes, <sup>13</sup>C. <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="Compounds" href="https://www.merriam-webster.com/dictionary/Compounds" data-type="MW">Compounds</a> made from the <sup>13</sup>C-enriched material are needed for certain medical tests, such as one that detects the ulcer-causing bacterium <em>Helicobacter pylori</em>.</p><span class="marker MOD3 mod-inline"></span></section> <section data-level="2" id="ref48266"><h2 class="h2">Chemical exchange reactions</h2> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Slight differences between the preferences of isotopes for one chemical form over another can serve as the basis for separation. The preparation of <a href="https://www.britannica.com/science/nitrogen" class="md-crosslink autoxref " data-show-preview="true">nitrogen</a> enriched in <sup>15</sup>N by ion-exchange techniques illustrates this principle. <a href="https://www.britannica.com/science/ammonia" class="md-crosslink " data-show-preview="true">Ammonia</a> in water NH<sub>3</sub>(aq) will bind to a so-called <a href="https://www.britannica.com/science/ion-exchange-resin" class="md-crosslink autoxref " data-show-preview="true">ion-exchange resin</a> (R–H). When poured over a vertical column of resin, a solution of ammonia reacts to form a well-defined horizontal band at the top of the column. The addition of a solution of <a href="https://www.britannica.com/science/lye" class="md-crosslink " data-show-preview="true">lye</a> (sodium hydroxide) will force the band of ammonia to move down the column. As the resin holds <sup>15</sup>NH<sub>3</sub> slightly more tenaciously than <sup>14</sup>NH<sub>3</sub>, the <sup>14</sup>NH<sub>3</sub> tends to concentrate at the leading, or bottom, edge of the band and the <sup>15</sup>NH<sub>3</sub> at the trailing, or topmost, edge. Solutions depleted or enriched in <sup>15</sup>N are collected as they wash off the column.</p><span class="marker MOD4 mod-inline"></span></section> <section data-level="2" id="ref48267"><h2 class="h2">Gaseous diffusion</h2> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">Gases can diffuse through the small pores present in many materials. The <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="diffusion" href="https://www.merriam-webster.com/dictionary/diffusion" data-type="MW">diffusion</a> proceeds in a random manner as gas molecules bounce off the walls of the porous medium. The average time a molecule of gas takes to <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="traverse" href="https://www.merriam-webster.com/dictionary/traverse" data-type="MW">traverse</a> such a barrier depends on its velocity and certain other factors. According to the <a href="https://www.britannica.com/science/kinetic-theory-of-gases" class="md-crosslink " data-show-preview="true">kinetic theory of gases</a>, at a given temperature a lighter molecule will have a larger average velocity than a heavier one. This result provides the basis for a separation method widely used to produce <a href="https://www.britannica.com/science/uranium" class="md-crosslink autoxref " data-show-preview="true">uranium</a> enriched in the readily <span id="ref496343"></span><a href="https://www.britannica.com/science/uranium-235" class="md-crosslink " data-show-preview="true">fissionable</a> isotope <sup>235</sup>U, which is needed for nuclear reactors and nuclear weapons. (Natural uranium contains only about 0.7 percent <sup>235</sup>U, with the remainder of the isotopic mixture consisting almost entirely of <sup>238</sup>U.) In the separation process, natural uranium in the form of uranium hexafluoride (UF<sub>6</sub>) gas is <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="diffused" href="https://www.britannica.com/dictionary/diffused" data-type="EB">diffused</a> from one compartment of a chamber to another through a porous barrier. Since the molecules of <sup>235</sup>UF<sub>6</sub> travel at a higher velocity than those of <sup>238</sup>UF<sub>6</sub>, they pass into the second compartment more rapidly than the latter. Because the percentage of <sup>235</sup>U increases only slightly after traversal of the barrier, the process must be repeated hundreds of thousands of times to obtain the desired concentration of the isotope.</p><div class="module-spacing"> </div><span class="marker MOD5 mod-inline"></span></section> <section data-level="2" id="ref48268"><h2 class="h2">Gas centrifugation</h2> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">When a mixture of gaseous molecules spins at high speed in a specially designed closed container, the heaviest species will concentrate near the outer walls and the lightest near the axis. The American physicist <span id="ref496345"></span>Jesse W. Beams used a gas <span id="ref496344"></span><a href="https://www.britannica.com/technology/centrifuge" class="md-crosslink " data-show-preview="true">centrifuge</a> to separate isotopes, specifically the isotopes of <a href="https://www.britannica.com/science/chlorine" class="md-crosslink autoxref " data-show-preview="true">chlorine</a>, for the first time in 1936. Much <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="subsequent" href="https://www.britannica.com/dictionary/subsequent" data-type="EB">subsequent</a> work focused on the separation of <sup>235</sup>UF<sub>6</sub> from <sup>238</sup>UF<sub>6</sub>, for which the gas centrifuge promised considerable savings in energy costs. Today, something less than 5 percent of the world’s enriched uranium is produced by this method. Gas centrifuge facilities also produce and sell gram-to-kilogram quantities of the isotopes of numerous other elements for scientific and medical purposes.</p><span class="marker MOD6 mod-inline"></span></section> <section data-level="2" id="ref48269"><h2 class="h2">Photochemical enrichment methods</h2> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">As discussed above, the frequencies of light absorbed by isotopes differ slightly. Once an <a href="https://www.britannica.com/science/atom" class="md-crosslink autoxref " data-show-preview="true">atom</a> has absorbed radiation and reached an excited state, its chemical properties may become quite different from what they were in the initial, or ground, state. Certain chemical and physical processes—the loss of an <a href="https://www.britannica.com/science/electron" class="md-crosslink autoxref " data-show-preview="true">electron</a>, for example—may proceed from an excited state that would not occur at all in the ground state. This observation is the nub of photochemical methods for isotope separation in which light is used to excite one and only one isotope of an element. In <span id="ref928827"></span>atomic vapour laser isotope separation (AVLIS), the starting material is the element itself; in <span id="ref928828"></span><a href="https://www.britannica.com/science/molecular-laser-isotope-separation" class="md-crosslink ">molecular laser isotope separation</a> (MLIS), the starting material is a <a href="https://www.britannica.com/science/chemical-compound" class="md-crosslink autoxref " data-show-preview="true">chemical compound</a> containing the element. Ordinary light sources are not suitable for isotope separation because they <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="emit" href="https://www.britannica.com/dictionary/emit" data-type="EB">emit</a> a broad range of frequencies that excites all the isotopes of an element. For this reason, the large-scale implementation of AVLIS and MLIS had to await improvements in <span id="ref496346"></span><a href="https://www.britannica.com/technology/laser" class="md-crosslink " data-show-preview="true">lasers</a>—devices that produce intense light within exquisitely narrow bands of frequencies.</p><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">The use of laser-based methods to separate the isotopes of uranium attracted great attention in the closing decades of the 20th century. Proponents foresaw that these methods would consume less energy and waste less starting material than, for example, gaseous diffusion plants. In several countries, government-sponsored research concentrated on processes that begin with ordinary metallic uranium. Upon heating in an oven, the uranium vaporizes and escapes as a <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="beam" href="https://www.britannica.com/dictionary/beam" data-type="EB">beam</a> of atoms through a small hole. Several large, high-powered lasers tuned to the correct frequencies shine on the beam and cause the <sup>235</sup>U atoms (but not the <sup>238</sup>U atoms) to lose electrons. In this (ionized) form the <sup>235</sup>U particles are attracted to and collect on a charged plate. Ironically, just as this technology came to maturity, various geopolitical factors—relatively abundant fossil fuels, a surfeit of weapons-grade uranium from Russia, progress toward nuclear disarmament, and concerns about the safety of nuclear reactors and about preserving jobs in the nuclear industry—idled the first large-scale laser-enrichment facility in the <a href="https://www.britannica.com/place/United-States" class="md-crosslink autoxref " data-show-preview="true">United States</a>. Even so, it seems safe to predict that laser separation will have a role to play in producing nuclear fuels.</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">Both government and private laboratories have been active in developing laser separation methods for rare stable isotopes of other elements. Such isotopes have applications in medicine and in the life sciences. They may serve, for example, as the starting material from which to make the radioactive isotopes needed for <a href="https://www.britannica.com/science/nuclear-medicine" class="md-crosslink autoxref " data-show-preview="true">nuclear medicine</a> or as tags put on drugs to monitor their action inside patients.</p><span class="marker MOD9 mod-inline"></span> <span class="md-signature font-12"><a href="/contributor/Gregory-F-Herzog/3392">Gregory F. Herzog</a></span></section></section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-simplify-root"></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":6,"pagesTotal":6,"pageId":296583,"pageLength":1215,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.36"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/topic-page.js?v=3.133.36' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":6,"hasSummarizeButton":false,"hasAskButton":true} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Isotope - Separation, Enrichment, Radioactive | Britannica