Radioactive isotope | Description, Uses, & Examples

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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 gtm-byline font-12 byline-contributor text-decoration-underline"> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <a class="byline-edit-history" href="https://www.britannica.com/science/radioactive-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 border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </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>Also called: </dt> <dd>radioisotope, radionuclide, or radioactive nuclide</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>Key People: </dt> <dd><a href="/biography/Harold-Urey" topicid="619727">Harold C. Urey</a></dd> <dd><a href="/biography/Friedrich-Adolf-Paneth" topicid="441198">Friedrich Adolf Paneth</a></dd> <dd><a href="/biography/Frederic-Joliot-Curie" topicid="305746">Frédéric Joliot-Curie</a></dd> <dd><a href="/biography/Irene-Joliot-Curie" topicid="305750">Irène Joliot-Curie</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/transuranium-element" topicid="603220">transuranium element</a></dd> <dd><a href="/science/isotopic-tracer" topicid="296664">isotopic tracer</a></dd> <dd><a href="/science/tritium" topicid="606002">tritium</a></dd> <dd><a href="/science/indium-115" topicid="286257">indium-115</a></dd> <dd><a href="/science/cesium-137" topicid="103804">cesium-137</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/radioactive-isotope"> See all related content </a> </div> </div> </div> </div><script type="application/ld+json"> { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type" : "Question", "name" : "<div>What is a radioactive isotope? <\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "A radioactive isotope, also known as a radioisotope, radionuclide, or radioactive nuclide, is any of several species of the same <a href=\"https:\/\/www.britannica.com\/science\/chemical-element\">chemical element<\/a> with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting <a href=\"https:\/\/www.britannica.com\/science\/radiation\">radiation<\/a> in the form of <a href=\"https:\/\/www.britannica.com\/science\/alpha-particle\">alpha<\/a>, <a href=\"https:\/\/www.britannica.com\/science\/beta-particle\">beta<\/a>, and <a href=\"https:\/\/www.britannica.com\/science\/gamma-ray\">gamma<\/a> rays. Every chemical element has one or more radioactive isotopes. For example, <a href=\"https:\/\/www.britannica.com\/science\/hydrogen\">hydrogen<\/a>, the lightest element, has three isotopes, which have mass numbers 1, 2, and 3. Only hydrogen-3 (<a href=\"https:\/\/www.britannica.com\/science\/tritium\">tritium<\/a>), however, is a radioactive isotope; the other two are stable. More than 1,800 radioactive isotopes of the various elements are known. Some of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products. Each \u201Cparent\u201D radioactive isotope eventually decays into one or at most a few stable isotope \u201Cdaughters\u201D specific to that parent. " } } , { "@type" : "Question", "name" : "<div>How are radioactive isotopes produced? <\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "There are several sources of radioactive isotopes. Some radioactive isotopes are present as terrestrial radiation. Radioactive isotopes of <a href=\"https:\/\/www.britannica.com\/science\/radium\">radium<\/a>, <a href=\"https:\/\/www.britannica.com\/science\/thorium\">thorium<\/a>, and <a href=\"https:\/\/www.britannica.com\/science\/uranium\">uranium<\/a>, for example, are found naturally in rocks and soil. Uranium and thorium also occur in trace amounts in water. <a href=\"https:\/\/www.britannica.com\/science\/radon\">Radon<\/a>, generated by the radioactive decay of radium, is present in air. Organic materials typically contain small amounts of radioactive <a href=\"https:\/\/www.britannica.com\/science\/carbon-chemical-element\">carbon<\/a> and <a href=\"https:\/\/www.britannica.com\/science\/potassium\">potassium<\/a>. Cosmic radiation from the Sun and other stars is a source of background radiation on Earth. Other radioactive isotopes are produced by humans via nuclear reactions, which result in unstable combinations of neutrons and protons. One way of artificially inducing nuclear transmutation is by bombarding stable isotopes with <a href=\"https:\/\/www.britannica.com\/science\/alpha-particle\">alpha particles<\/a>. " } } , { "@type" : "Question", "name" : "<div>How are radioactive isotopes used in medicine? <\/div><em><\/em>", "acceptedAnswer" : { "@type" : "Answer", "text" : "Radioactive isotopes have many useful applications. In particular, they are central to the fields of <a href=\"https:\/\/www.britannica.com\/science\/nuclear-medicine\">nuclear medicine<\/a> and <a href=\"https:\/\/www.britannica.com\/science\/radiation-therapy\">radiotherapy<\/a>. In nuclear medicine, tracer radioisotopes may be taken orally or be injected or inhaled into the body. The radioisotope circulates through the body or is taken up only by certain tissues. Its distribution can be tracked according to the radiation it gives off. In radiotherapy, radioisotopes typically are employed to destroy diseased cells. Radiotherapy commonly is used to treat <a href=\"https:\/\/www.britannica.com\/science\/cancer-disease\">cancer<\/a> and other conditions involving abnormal tissue growth, such as <a href=\"https:\/\/www.britannica.com\/science\/hyperthyroidism\">hyperthyroidism<\/a>. Beams of subatomic particles, such as protons, neutrons, or alpha or beta particles, directed toward diseased tissues can disrupt the atomic or molecular structure of abnormal cells, causing them to die. Medical applications use artificial radioisotopes that have been produced from stable isotopes bombarded with neutrons. " } } ] } </script> <div class="top-questions qa-accordion d-flex flex-column module-spacing"><div class="font-weight-bold font-14 mb-5"> Top Questions </div><div id="intent-accordion" class="md-intent-accordion"><div class="top-question bg-gray-50 rounded" data-value="1"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>What is a radioactive isotope? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>A radioactive isotope, also known as a radioisotope, radionuclide, or radioactive nuclide, is any of several species of the same <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">chemical element</a> with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting <a href="https://www.britannica.com/science/radiation" class="md-crosslink " data-show-preview="true">radiation</a> in the form of <a href="https://www.britannica.com/science/alpha-particle" class="md-crosslink " data-show-preview="true">alpha</a>, <a href="https://www.britannica.com/science/beta-particle" class="md-crosslink " data-show-preview="true">beta</a>, and <a href="https://www.britannica.com/science/gamma-ray" class="md-crosslink " data-show-preview="true">gamma</a> rays. Every chemical element has one or more radioactive isotopes. For example, <a href="https://www.britannica.com/science/hydrogen" class="md-crosslink " data-show-preview="true">hydrogen</a>, the lightest element, has three isotopes, which have mass numbers 1, 2, and 3. Only hydrogen-3 (<a href="https://www.britannica.com/science/tritium" class="md-crosslink " data-show-preview="true">tritium</a>), however, is a radioactive isotope; the other two are stable. More than 1,800 radioactive isotopes of the various elements are known. Some of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products. Each “parent” radioactive isotope eventually decays into one or at most a few stable isotope “daughters” specific to that parent. </p></div><div class="connections border-top mt-15"><a href="/science/radiation" class="d-flex mt-15">radiation</a>Learn more about radiation.</div></div></div><div class="top-question bg-gray-50 rounded" data-value="2"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>How are radioactive isotopes produced? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>There are several sources of radioactive isotopes. Some radioactive isotopes are present as terrestrial radiation. Radioactive isotopes of <a href="https://www.britannica.com/science/radium" class="md-crosslink " data-show-preview="true">radium</a>, <a href="https://www.britannica.com/science/thorium" class="md-crosslink " data-show-preview="true">thorium</a>, and <a href="https://www.britannica.com/science/uranium" class="md-crosslink " data-show-preview="true">uranium</a>, for example, are found naturally in rocks and soil. Uranium and thorium also occur in trace amounts in water. <a href="https://www.britannica.com/science/radon" class="md-crosslink " data-show-preview="true">Radon</a>, generated by the radioactive decay of radium, is present in air. Organic materials typically contain small amounts of radioactive <a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink " data-show-preview="true">carbon</a> and <a href="https://www.britannica.com/science/potassium" class="md-crosslink " data-show-preview="true">potassium</a>. Cosmic radiation from the Sun and other stars is a source of background radiation on Earth. Other radioactive isotopes are produced by humans via nuclear reactions, which result in unstable combinations of neutrons and protons. One way of artificially inducing nuclear transmutation is by bombarding stable isotopes with <a href="https://www.britannica.com/science/alpha-particle" class="md-crosslink " data-show-preview="true">alpha particles</a>. </p></div></div></div><div class="top-question bg-gray-50 rounded" data-value="3"><h3 class="accordion--question font-14 font-weight-normal cursor-pointer rounded"><div class="pe-none d-flex justify-content-between align-items-center"><div>How are radioactive isotopes used in medicine? </div><em class="material-icons" data-icon="expand_more"></em></div></h3><div class="accordion--answer hidden p-15 pt-5 font-16 mb-5"><div class="accordion--answer-copy"><p>Radioactive isotopes have many useful applications. In particular, they are central to the fields of <a href="https://www.britannica.com/science/nuclear-medicine" class="md-crosslink " data-show-preview="true">nuclear medicine</a> and <a href="https://www.britannica.com/science/radiation-therapy" class="md-crosslink " data-show-preview="true">radiotherapy</a>. In nuclear medicine, tracer radioisotopes may be taken orally or be injected or inhaled into the body. The radioisotope circulates through the body or is taken up only by certain tissues. Its distribution can be tracked according to the radiation it gives off. In radiotherapy, radioisotopes typically are employed to destroy diseased cells. Radiotherapy commonly is used to treat <a href="https://www.britannica.com/science/cancer-disease" class="md-crosslink " data-show-preview="true">cancer</a> and other conditions involving abnormal tissue growth, such as <a href="https://www.britannica.com/science/hyperthyroidism" class="md-crosslink " data-show-preview="true">hyperthyroidism</a>. Beams of subatomic particles, such as protons, neutrons, or alpha or beta particles, directed toward diseased tissues can disrupt the atomic or molecular structure of abnormal cells, causing them to die. Medical applications use artificial radioisotopes that have been produced from stable isotopes bombarded with neutrons. </p><div class="continue-reading"> Read more below: <a href="/story/how-radioactive-isotopes-are-used-in-medicine">How Radioactive Isotopes are Used in Medicine</a></div></div><div class="connections border-top mt-15"><a href="/science/nuclear-medicine" class="d-flex mt-15">nuclear medicine</a>Learn more about the field of nuclear medicine, which employs radioactive isotopes in the diagnosis and treatment of disease.</div><div class="connections border-top mt-15"><a href="/science/radiation-therapy" class="d-flex mt-15">radiation therapy</a>Learn more about radiotherapy, the use of radioisotopes to destroy diseased cells.</div></div></div></div></div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref273988"></span>radioactive isotope</strong>, any of several species of the same <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">chemical element</a> with different masses whose nuclei are unstable and <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="dissipate" href="https://www.britannica.com/dictionary/dissipate" data-type="EB">dissipate</a> excess energy by spontaneously emitting <a href="https://www.britannica.com/science/radiation" class="md-crosslink " data-show-preview="true">radiation</a> in the form of <a href="https://www.britannica.com/science/alpha-particle" class="md-crosslink " data-show-preview="true">alpha</a>, <a href="https://www.britannica.com/science/beta-particle" class="md-crosslink " data-show-preview="true">beta</a>, and <a href="https://www.britannica.com/science/gamma-ray" class="md-crosslink " data-show-preview="true">gamma rays</a>.</p><span class="marker MOD1 mod-inline"></span><span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">A brief treatment of radioactive isotopes follows. For full treatment, <em>see</em> <a href="https://www.britannica.com/science/isotope/The-discovery-of-isotopes#ref48251" class="md-crosslink " data-show-preview="true">isotope: Radioactive isotopes</a>.</p><span class="marker MOD2 mod-inline"></span><span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">Every chemical element has one or more radioactive isotopes. For example, <span id="ref273989"></span><a href="https://www.britannica.com/science/hydrogen" class="md-crosslink " data-show-preview="true">hydrogen</a>, the lightest element, has three isotopes with mass numbers 1, 2, and 3. Only hydrogen-3 (<span id="ref273990"></span><a href="https://www.britannica.com/science/tritium" class="md-crosslink " data-show-preview="true">tritium</a>), however, is a radioactive <a href="https://www.britannica.com/science/isotope" class="md-crosslink autoxref " data-show-preview="true">isotope</a>, the other two being stable. More than 1,000 radioactive isotopes of the various elements are known. Approximately 50 of these are found in nature; the rest are produced artificially as the direct products of <a href="https://www.britannica.com/science/nuclear-reaction" class="md-crosslink " data-show-preview="true">nuclear reactions</a> or indirectly as the radioactive descendants of these products.</p><a class="link-module shadow-sm d-block qa-read-more-module" href="/science/isotope/The-discovery-of-isotopes#ref496316" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/64/216564-138-51A467D7/What-are-isotopes.jpg" alt="What are isotopes and how do they work?" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-navy-dark">More From Britannica</div> <div class="font-weight-semi-bold mt-5">isotope: Radioactive isotopes</div> </div> </a><span class="marker MOD3 mod-inline"></span><span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Radioactive isotopes have many useful applications. In <span id="ref273992"></span><a href="https://www.britannica.com/science/medicine" class="md-crosslink " data-show-preview="true">medicine</a>, for example, <span id="ref273993"></span><a href="https://www.britannica.com/science/cobalt-chemical-element" class="md-crosslink " data-show-preview="true">cobalt</a>-60 is extensively employed as a radiation source to arrest the development of <a href="https://www.britannica.com/science/cancer-disease" class="md-crosslink " data-show-preview="true">cancer</a>. Other radioactive isotopes are used as tracers for <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="diagnostic" href="https://www.britannica.com/dictionary/diagnostic" data-type="EB">diagnostic</a> purposes as well as in research on metabolic processes. When a radioactive isotope is added in small amounts to comparatively large quantities of the stable element, it behaves exactly the same as the ordinary isotope chemically; it can, however, be traced with a <a href="https://www.britannica.com/technology/Geiger-counter" class="md-crosslink " data-show-preview="true">Geiger counter</a> or other detection device. <span id="ref273994"></span><a href="https://www.britannica.com/science/iodine" class="md-crosslink " data-show-preview="true">Iodine</a>-131 has proved effective in treating <a href="https://www.britannica.com/science/hyperthyroidism" class="md-crosslink " data-show-preview="true">hyperthyroidism</a>. Another medically important radioactive isotope is <span id="ref273995"></span><a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink " data-show-preview="true">carbon</a>-14, which is used in a breath test to detect the <a href="https://www.britannica.com/science/ulcer" class="md-crosslink " data-show-preview="true">ulcer</a>-causing <a href="https://www.britannica.com/science/bacteria" class="md-crosslink " data-show-preview="true">bacteria</a> <em>Heliobacter pylori</em>.</p><span class="marker MOD4 mod-inline"></span><span class="marker PREMOD5 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="245584" data-asm-type="video"><div class="md-assembly-wrapper card-media " data-type="video" video-id="214985"><a data-id="214985" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/Nuclear-medicine-overview-radioactive-isotopes-in-medicine/-245584"><img src="https://cdn.britannica.com/85/214985-138-75B0DE3A/Nuclear-medicine-overview-radioactive-isotopes-in-medicine.jpg?w=800&h=450&c=crop" alt="Using nuclear medicine to diagnose and treat diseases" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/Hw8O6sQf.m3u8" } ], "image": "https://cdn.britannica.com/85/214985-138-75B0DE3A/Nuclear-medicine-overview-radioactive-isotopes-in-medicine.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/XoOC6sdb", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/ksNw2lgT.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="214985">Using nuclear medicine to diagnose and treat diseases</span><span>Overview of the use of radioactive isotopes in medicine to diagnose certain ailments.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div><a class="font-14 mt-10 d-inline-block" href="/science/radioactive-isotope/images-videos">See all videos for this article</a></figcaption></figure></div></div><p class="topic-paragraph">In <span id="ref273996"></span><a href="https://www.britannica.com/money/industry" class="md-crosslink " data-show-preview="true">industry</a>, radioactive isotopes of various kinds are used for measuring the thickness of <a href="https://www.britannica.com/science/metal-chemistry" class="md-crosslink " data-show-preview="true">metal</a> or <a href="https://www.britannica.com/science/plastic" class="md-crosslink " data-show-preview="true">plastic</a> sheets; their precise thickness is indicated by the strength of the radiations that penetrate the material being inspected. They also may be employed in place of large <a href="https://www.britannica.com/science/X-ray" class="md-crosslink " data-show-preview="true">X-ray</a> machines to examine manufactured metal parts for structural defects. Other significant applications include the use of radioactive isotopes as compact sources of <span id="ref273997"></span><a href="https://www.britannica.com/technology/electric-power" class="md-crosslink " data-show-preview="true">electrical power</a>—e.g., <a href="https://www.britannica.com/science/plutonium" class="md-crosslink " data-show-preview="true">plutonium</a>-238 in <a href="https://www.britannica.com/technology/spacecraft" class="md-crosslink autoxref " data-show-preview="true">spacecraft</a>. In such cases, the <a href="https://www.britannica.com/science/heat" class="md-crosslink " data-show-preview="true">heat</a> produced in the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="decay" href="https://www.britannica.com/dictionary/decay" data-type="EB">decay</a> of the radioactive isotope is converted into <a href="https://www.britannica.com/science/electricity" class="md-crosslink " data-show-preview="true">electricity</a> by means of thermoelectric junction circuits or related devices.</p><div class="one-good-fact-module"> </div><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The <span id="ref4803"></span>table lists some naturally occurring radioactive isotopes.</p><span class="marker MOD6 mod-inline"></span><span class="md-raw-html"><div class="md-drag md-table-wrapper"><table> <caption> Some significant naturally occurring radioactive isotopes </caption> <thead> <tr> <th scope="col"> isotope </th> <th scope="col"> half-life (years, unless noted) </th> </tr> </thead> <tfoot> <tr> <td colspan="2"> Source: National Nuclear Data Center, Brookhaven National Laboratory, NuDat 2.6 (2016). </td> </tr> </tfoot> <tbody> <tr> <td scope="row"> <sup>3</sup>H </td> <td> 12.32 </td> </tr> <tr> <td scope="row"> <sup>14</sup>C </td> <td> 5,700 </td> </tr> <tr> <td scope="row"> <sup>50</sup>V </td> <td> >2.1 × 10<sup>17</sup> </td> </tr> <tr> <td scope="row"> <sup>87</sup>Rb </td> <td> 4.81 × 10<sup>10</sup> </td> </tr> <tr> <td scope="row"> <sup>90</sup>Sr </td> <td> 28.9 </td> </tr> <tr> <td scope="row"> <sup>115</sup>In </td> <td> 4.41 × 10<sup>14</sup> </td> </tr> <tr> <td scope="row"> <sup>123</sup>Te </td> <td> >9.2 × 10<sup>16</sup> </td> </tr> <tr> <td scope="row"> <sup>130</sup>Te </td> <td> >3.0 × 10<sup>24</sup> </td> </tr> <tr> <td scope="row"> <sup>131</sup>I </td> <td> 8.0252 days </td> </tr> <tr> <td scope="row"> <sup>137</sup>Cs </td> <td> 30.08 </td> </tr> <tr> <td scope="row"> <sup>138</sup>La </td> <td> 1.02 × 10<sup>11</sup> </td> </tr> <tr> <td scope="row"> <sup>144</sup>Nd </td> <td> 2.29 × 10<sup>15</sup> </td> </tr> <tr> <td scope="row"> <sup>147</sup>Sm </td> <td> 1.06 × 10<sup>11</sup> </td> </tr> <tr> <td scope="row"> <sup>148</sup>Sm </td> <td> 7 × 10<sup>15</sup> </td> </tr> <tr> <td scope="row"> <sup>176</sup>Lu </td> <td> 3.76 × 10<sup>10</sup> </td> </tr> <tr> <td scope="row"> <sup>187</sup>Re </td> <td> 4.33 × 10<sup>10</sup> </td> </tr> <tr> <td scope="row"> <sup>186</sup>Os </td> <td> 2 × 10<sup>15</sup> </td> </tr> <tr> <td scope="row"> <sup>222</sup>Rn </td> <td> 3.8235 days </td> </tr> <tr> <td scope="row"> <sup>226</sup>Ra </td> <td> 1,600 </td> </tr> <tr> <td scope="row"> <sup>230</sup>Th </td> <td> 75,400 </td> </tr> <tr> <td scope="row"> <sup>232</sup>Th </td> <td> 1.4 × 10<sup>10</sup> </td> </tr> <tr> <td scope="row"> <sup>232</sup>U </td> <td> 68.9 </td> </tr> <tr> <td scope="row"> <sup>234</sup>U </td> <td> 245,500 </td> </tr> <tr> <td scope="row"> <sup>235</sup>U </td> <td> 7.04 × 10<sup>8</sup> </td> </tr> <tr> <td scope="row"> <sup>236</sup>U </td> <td> 2.342 × 10<sup>7</sup> </td> </tr> <tr> <td scope="row"> <sup>237</sup>U </td> <td> 6.75 days </td> </tr> <tr> <td scope="row"> <sup>238</sup>U </td> <td> 4.468 × 10<sup>9</sup> </td> </tr> </tbody> </table></div> </span> </section> <span class="md-signature"><a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></span> <span class="md-signature">This article was most recently revised and updated by <a href="/editor/Adam-Augustyn/6394">Adam Augustyn</a>.</span><span class="marker end-of-content"></span><span class="marker after-article"></span></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 type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; 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