Alpha particle | Charge, Mass, & Definition

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class="md-content"> <div class="md-article-container template-desktop"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content " data-topic-id="17152"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex 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/alpha-particle">alpha particle</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> <span class="toc-extra-link selected link-gray-900 mt-15"> Introduction </span> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/alpha-particle/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/alpha-particle">Quick Facts & Related Topics</a> </div> <div class="mb-30 tlr-related-questions"> <div class="text-gray-900 p-5 pb-0 font-serif font-14 font-weight-bold mx-10 mb-15"> Related Questions </div> <ul> <li class="link-gray-900 mb-15"><a class="" href="/question/Why-does-physics-work-in-SI-units">Why does physics work in SI units?</a> </li> <li class="link-gray-900 mb-15"><a class="" 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Let us know if you have suggestions to improve this article (requires login). </div> <div class="type-menu"> <label for="feedback-type" class="label mb-10">Feedback Type</label> <select id="feedback-type" class="form-select mb-30" name="feedbackTypeId" required> <option value="" selected="selected">Select a type (Required)</option> <option value="1">Factual Correction</option> <option value="2">Spelling/Grammar Correction</option> <option value="3">Link Correction</option> <option value="4">Additional Information</option> <option value="5">Other</option> </select> </div> <label for="feedback" class="label mb-10">Your Feedback</label> <textarea id="feedback" class="form-control mb-30" name="feedback" maxlength="3000" rows="7" required></textarea> <button class="btn btn-blue" type="submit">Submit Feedback</button> </form> <div class="success-messaging d-none mt-30"> <div class="title">Thank you for your feedback</div> <p>Our editors will review what you’ve submitted and determine whether to revise the article.</p> </div> </div> </div> <div class="md-websites-modal size-lg d-none"> <div class="md-modal-body"> <div class="h2 font-serif pb-15 border-bottom font-weight-bold"> External Websites </div> <div class="pb-20"> <ul class="list-unstyled mt-20 lh-lg"> <li><a class="external" href="https://pmc.ncbi.nlm.nih.gov/articles/PMC6525335/" target="_blank" rel="noopener ">National Center for Biotechnology Information - PubMed Central - Tracking down alpha-particles: the design, characterisation and testing of a shallow-angled alpha-particle irradiator</a></li> <li><a class="external" href="https://www.nature.com/articles/s41598-023-31748-9" target="_blank" rel="noopener ">Nature - Scientific Reports - Development of an ultrahigh resolution real time alpha particle imaging system for observing the trajectories of alpha particles in a scintillator</a></li> <li><a class="external" href="https://www.space.com/alpha-particles-alpha-radiation" target="_blank" rel="noopener ">Space.com - Alpha particles and alpha radiation: Explained</a></li> <li><a class="external" href="https://www.osti.gov/opennet/manhattan-project-history/Science/Radioactivity/alpha.html" target="_blank" rel="noopener ">U.S. Department of Energy - The Manhattan Project - Alpha Particles</a></li> </ul> </div> </div> </div> </div> </div> <div class="toc-header-marker"></div> <button class="ai-ask-button btn border-2 js-header-ai-ask-button d-none btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10"> Ask the Chatbot a Question </button> <div class="caption alternate-titles">Also known as: helium-4 nucleus</div> <div class="md-byline module-spacing "> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written and fact-checked by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. 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"> <span class="text-gray-700"> Last Updated: <time datetime="2024-11-21T00:00:00CST" >Nov 21, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/alpha-particle/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>Related Topics: </dt> <dd><a href="/science/helium-chemical-element" topicid="260101">helium</a></dd> <dd><a href="/science/helium-4" topicid="260186">helium-4</a></dd> <dd><a href="/science/atomic-nucleus" topicid="41712">atomic nucleus</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/alpha-particle"> See all related content </a> </div> </div> </div> </div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="https://www.cbc.ca/news/health/cancer-treatment-research-targeted-alpha-therapy-1.7384434" rel="nofollow">Killing cancer cells with alpha particles could be the next frontier in treatment</a> <span class="font-14 text-gray-600"> <span>•</span> Nov. 15, 2024, 11:37 PM ET (CBC) </span> </div> </div> <div class="rest-of-recent-news-items"> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </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="ref191725"></span>alpha particle</strong>, positively charged particle, identical to the nucleus of the <span id="ref191726"></span><a href="https://www.britannica.com/science/helium-chemical-element" class="md-crosslink " data-show-preview="true">helium</a>-4 <a href="https://www.britannica.com/science/atom" class="md-crosslink " data-show-preview="true">atom</a>, spontaneously <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="emitted" href="https://www.britannica.com/dictionary/emitted" data-type="EB">emitted</a> by some <a href="https://www.britannica.com/science/radioactivity" class="md-crosslink " data-show-preview="true">radioactive</a> substances, consisting of two <a href="https://www.britannica.com/science/proton-subatomic-particle" class="md-crosslink " data-show-preview="true">protons</a> and two <a href="https://www.britannica.com/science/neutron" class="md-crosslink " data-show-preview="true">neutrons</a> bound together, thus having a mass of four <a href="https://www.britannica.com/science/atomic-mass" class="md-crosslink " data-show-preview="true">units</a> and a positive <a href="https://www.britannica.com/science/electric-charge" class="md-crosslink autoxref " data-show-preview="true">charge</a> of two. Discovered and named (1899) by <span id="ref191727"></span><a href="https://www.britannica.com/biography/Ernest-Rutherford" class="md-crosslink " data-show-preview="true">Ernest Rutherford</a>, alpha particles were used by him and coworkers in experiments to probe the structure of atoms in thin metallic foils. This work resulted in the <a href="https://www.britannica.com/science/Rutherford-model" class="md-crosslink " data-show-preview="true">first concept of the atom as a tiny planetary system</a> with negatively charged particles (electrons) orbiting around a positively charged nucleus (1909–11). Later, <span id="ref1261500"></span><a href="https://www.britannica.com/biography/Patrick-Blackett-Baron-Blackett" class="md-crosslink " data-show-preview="true">Patrick Blackett</a> bombarded <a href="https://www.britannica.com/science/nitrogen" class="md-crosslink " data-show-preview="true">nitrogen</a> with alpha particles, changing it to <a href="https://www.britannica.com/science/oxygen" class="md-crosslink " data-show-preview="true">oxygen</a>, in the first artificially produced <span id="ref894359"></span><a href="https://www.britannica.com/science/transmutation" class="md-crosslink " data-show-preview="true">nuclear transmutation</a> (1925). Today, alpha particles are produced for use as projectiles in nuclear research by ionization—i.e., by stripping both electrons from helium atoms—and then <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="accelerating" href="https://www.britannica.com/dictionary/accelerating" data-type="EB">accelerating</a> the now positively charged particle to high energies.</p><span class="marker MOD1 mod-inline"></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/Erik-Gregersen/6723">Erik Gregersen</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 || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <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":1,"pagesTotal":1,"pageId":17152,"pageLength":146,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"D","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"SMALL","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </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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Alpha particle | Charge, Mass, & Definition | Britannica