{"id":12672,"date":"2016-09-12T14:03:12","date_gmt":"2016-09-12T14:03:12","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=12672"},"modified":"2022-10-18T09:54:24","modified_gmt":"2022-10-18T09:54:24","slug":"direct-nuclear-reactions","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/direct-nuclear-reactions\/","title":{"rendered":"Direct Nuclear Reactions"},"content":{"rendered":"<div   id="8n9s8rpp6h"    class=\"su-quote su-quote-style-default\"><div   id="8n9s8rpp6h"    class=\"su-quote-inner su-u-clearfix su-u-trim\">Nuclear reactions that occur in a <strong>time comparable to the time of transit<\/strong> of an incident particle across the nucleus (~10<sup>-22<\/sup> s) are called <strong>direct nuclear reactions.<\/strong> Interaction time is critical for defining the reaction mechanism. The very short interaction time allows for an<strong> interaction of a single nucleon<\/strong> only (in extreme cases).<\/div><\/div>\n<p><strong><span style=\"font-weight: 400;\">To understand the nature of nuclear reactions, the classification according to <strong>the time scale<\/strong> of these reactions has to be introduced. Interaction time is critical for defining the reaction mechanism.<\/span><\/strong><\/p>\n<p><span style=\"font-weight: 400;\">There are <strong>two extreme scenarios<\/strong> for nuclear reactions (not only <a title=\"Neutron Nuclear Reactions\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/\">neutron nuclear reactions<\/a>): <\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\">A projectile and a target nucleus are within the range of nuclear forces for <\/span><b>a very short time<\/b><span style=\"font-weight: 400;\"> allowing for an <\/span><b>interaction of a single nucleon only<\/b><span style=\"font-weight: 400;\">. These types of reactions are called <\/span><b>direct nuclear reactions<\/b><span style=\"font-weight: 400;\">.<\/span><\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\">A projectile and a target nucleus are within the range of nuclear forces, allowing for a<\/span><b> large number of interactions between nucleons<\/b><span style=\"font-weight: 400;\">. These types of reactions are called the <\/span><a title=\"Compound Nucleus Reactions\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/compound-nucleus-reactions\/\"><b>compound nucleus reactions<\/b><\/a><span style=\"font-weight: 400;\">. <\/span><\/li>\n<\/ul>\n<h2>Direct Nuclear Reactions<\/h2>\n<p>Nuclear reactions that occur in a <strong>time comparable to the time of transit<\/strong> of an incident particle across the nucleus (~10<sup>-22<\/sup> s) are called <strong>direct nuclear reactions.<\/strong> Interaction time is critical for defining the reaction mechanism. The very short interaction time allows for an<strong> interaction of a single nucleon<\/strong> only (in extreme cases). There is always some non-direct (multiple internuclear interactions) component in all reactions, but the direct reactions have this component limited. The reaction has to occur <strong>at high energy <\/strong>to limit the time available for multiple internuclear interactions.<\/p>\n<p>Direct reactions have another very important property.<strong> Products<\/strong> of a direct reaction <strong>are not distributed isotropically in angle<\/strong>, but they are forward-focused. This reflects that the projectiles make only one, or very few, collisions with nucleons in the target nucleus, and its forward momentum is not transferred to an entire compound state.<\/p>\n<p><a title=\"Neutron cross-section\" href=\"http:\/\/sitepourvtc.com\/neutron-cross-section\/\">The cross-sections<\/a> for direct reactions vary smoothly and slowly with energy in contrast to the compound nucleus reactions. These cross-sections are comparable to the geometrical cross-sections of target nuclei. Types of direct reactions:<\/p>\n<ul>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><a title=\"Neutron Elastic Scattering\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-elastic-scattering\/\"><strong>Elastic scattering<\/strong><\/a> in which a passing particle and targes stay in their ground states. \u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><a title=\"Neutron Inelastic Scattering\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/neutron-inelastic-scattering\/\"><strong>Inelastic scattering<\/strong><\/a> in which a passing particle changes its energy state. \u00a0For example, the (p, p\u2019) reaction.<\/span><\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><strong>Transfer reactions<\/strong> in which one or more nucleons are transferred to the other nucleus. These reactions are further classified as:<\/span>\n<ul>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><strong>Stripping reaction<\/strong> in which one or more nucleons are transferred to a target nucleus from passing particles. For example, the neutron stripping in the (d, p) reaction.<\/span><\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><strong>Pick-up reaction<\/strong> in which one or more nucleons are transferred from a target nucleus to a passing particle. For example, the neutron pick-up in the (p, d) reaction.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><strong>Break-up reaction<\/strong> in which a breakup of a projectile into two or more fragments occurs.<\/span><\/li>\n<li style=\"font-weight: 400;\"><span style=\"font-weight: 400;\"><strong>Knock-out reaction<\/strong> in which a single nucleon or a light cluster is removed from the projectile by a collision with the target.<\/span><\/li>\n<\/ul>\n<p><a href=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/direct-nuclear-reaction.png\"><img loading=\"lazy\" class=\"aligncenter size-full wp-image-12664\" src=\"http:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/direct-nuclear-reaction.png\" alt=\"Direct nuclear reaction\" width=\"589\" height=\"83\" srcset=\"https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/direct-nuclear-reaction.png 589w, https:\/\/sitepourvtc.com\/wp-content\/uploads\/2015\/09\/direct-nuclear-reaction-300x42.png 300w\" sizes=\"(max-width: 589px) 100vw, 589px\" \/><\/a><\/p>\n<p style=\"text-align: center;\"><span style=\"font-weight: 400;\">Example: This threshold reaction of a fast neutron with an isotope <a title=\"Boron 10\" href=\"http:\/\/sitepourvtc.com\/glossary\/boron-10\/\"><sup>10<\/sup>B<\/a> is one of the ways how radioactive tritium in the primary circuit of all <\/span><a href=\"http:\/\/sitepourvtc.com\/pwr-pressurized-water-reactor\/\"><span style=\"font-weight: 400;\">PWRs<\/span><\/a><span style=\"font-weight: 400;\"> is generated.<\/span><\/p>\n<h2>Direct Reactions vs. Compound Nucleus Reactions<\/h2>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><div   id="8n9s8rpp6h"    class=\"su-spacer\" style=\"height:10px\"><\/div>\n<h2>Direct Reactions<\/h2>\n<ul>\n<li>The direct reactions are fast and involve a <strong>single-nucleon interaction<\/strong>.<\/li>\n<li>The interaction time must be very short<strong> (~10<sup>-22<\/sup> s)<\/strong>.<\/li>\n<li>The direct reactions require incident particle energy <strong>larger than \u223c 5 MeV\/Ap<\/strong>. (Ap is the atomic mass number of a projectile)<\/li>\n<li>Incident particles interact <strong>on the surface<\/strong> of a target nucleus rather than in the volume of a target nucleus.<\/li>\n<li>Products of the direct reactions <strong>are not distributed isotropically in angle<\/strong>, but they are forward-focused.<\/li>\n<li>Direct reactions are of importance in measurements of nuclear structure.<\/li>\n<\/ul>\n<\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-50 lgc-tablet-grid-50 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><div   id="8n9s8rpp6h"    class=\"su-spacer\" style=\"height:10px\"><\/div>\n<h2>Compound Nucleus Reactions<\/h2>\n<ul>\n<li><a title=\"Compound Nucleus Reactions\" href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/compound-nucleus-reactions\/\">The compound nucleus reactions<\/a> involve <strong>many nucleon-nucleon interactions<\/strong>.<\/li>\n<li>A large number of collisions between the nucleons leads to a <strong>thermal equilibrium<\/strong> inside the compound nucleus.<\/li>\n<li>The time scale of compound nucleus reactions is <strong>10<sup>-18<\/sup> s &#8211; 10<sup>-16<\/sup> s<\/strong>.<\/li>\n<li>The compound nucleus reactions are usually created if the projectile has <strong>low energy<\/strong>.<\/li>\n<li>Incident particles interact in the volume of a target nucleus.<\/li>\n<li>Products of the compound nucleus reactions are distributed <strong>near isotropically in angle<\/strong> (the nucleus loses memory of how it was created &#8211; <em><strong>Bohr\u2019s hypothesis of independence<\/strong><\/em>).<\/li>\n<li><strong>The decay mode<\/strong>\u00a0of the compound nucleus <strong>does not depend on how the compound nucleus is formed<\/strong>.<\/li>\n<li>Resonances in the cross-section are typical for the compound nucleus reaction.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-100 lgc-tablet-grid-100 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\"><\/div><\/div>\u00a0 <div   id="8n9s8rpp6h"    class=\"su-accordion su-u-trim\"><div   id="8n9s8rpp6h"    class=\"su-spoiler su-spoiler-style-default su-spoiler-icon-plus su-spoiler-closed\" data-scroll-offset=\"0\"><div   id="8n9s8rpp6h"    class=\"su-spoiler-title\" tabindex=\"0\" role=\"button\"><span class=\"su-spoiler-icon\"><\/span>References:<\/div><div   id="8n9s8rpp6h"    class=\"su-spoiler-content su-u-clearfix su-u-trim\"><strong>Nuclear and Reactor Physics:<\/strong>\n<ol>\n<li>J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading,\u00a0MA (1983).<\/li>\n<li>J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.<\/li>\n<li>W. M. Stacey, Nuclear Reactor Physics, John Wiley &amp; Sons, 2001, ISBN: 0- 471-39127-1.<\/li>\n<li>Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering,\u00a0Springer; 4th edition, 1994, ISBN:\u00a0978-0412985317<\/li>\n<li>W.S.C. Williams. Nuclear and Particle Physics.\u00a0Clarendon Press; 1 edition, 1991, ISBN:\u00a0978-0198520467<\/li>\n<li>G.R.Keepin. Physics of Nuclear Kinetics.\u00a0Addison-Wesley Pub. Co; 1st edition, 1965<\/li>\n<\/ol>\n<p><strong><\/strong><strong>Advanced Reactor Physics:<\/strong><\/p>\n<ol>\n<li>K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.<\/li>\n<li>K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.<\/li>\n<li><span style=\"font-weight: 400;\">D. L. Hetrick, Dynamics of Nuclear Reactors, American Nuclear Society, 1993, ISBN: 0-894-48453-2.\u00a0<\/span><\/li>\n<li>E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.<\/li>\n<\/ol>\n<\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-dotted\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><\/div><\/div><div   id="8n9s8rpp6h"    class=\"su-divider su-divider-style-default\" style=\"margin:15px 0;border-width:2px;border-color:#999999\"><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See previous:<\/h2>\n<a href=\"\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See above:<\/h2>\n<p>Neutron Nuclear Reactions<a href=\"http:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/p><\/div><\/div><div   id="8n9s8rpp6h"     class=\"lgc-column lgc-grid-parent lgc-grid-33 lgc-tablet-grid-33 lgc-mobile-grid-100 lgc-equal-heights \"><div   id="8n9s8rpp6h"     class=\"inside-grid-column\">\n<h2>See next:<\/h2>\n<a href=\"\" class=\"su-button su-button-style-flat\" style=\"color:#606060;background-color:#ffffff;border-color:#cccccc;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px\" target=\"_self\"><span style=\"color:#606060;padding:7px 20px;font-size:16px;line-height:24px;border-color:#ffffff;border-radius:10px;-moz-border-radius:10px;-webkit-border-radius:10px;text-shadow:0px 0px 0px #000000;-moz-text-shadow:0px 0px 0px #000000;-webkit-text-shadow:0px 0px 0px #000000\"><i class=\"sui sui-link\" style=\"font-size:16px;color:#5d5d5d\"><\/i> <\/span><\/a><\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>To understand the nature of nuclear reactions, the classification according to the time scale of these reactions has to be introduced. Interaction time is critical for defining the reaction mechanism. There are two extreme scenarios for nuclear reactions (not only neutron nuclear reactions): A projectile and a target nucleus are within the range of nuclear &#8230; <a title=\"Direct Nuclear Reactions\" class=\"read-more\" href=\"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-engineering-fundamentals\/neutron-nuclear-reactions\/direct-nuclear-reactions\/\" aria-label=\"More on Direct Nuclear Reactions\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":12656,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"generate_page_header":""},"_links":{"self":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12672"}],"collection":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/comments?post=12672"}],"version-history":[{"count":3,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12672\/revisions"}],"predecessor-version":[{"id":32666,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12672\/revisions\/32666"}],"up":[{"embeddable":true,"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/pages\/12656"}],"wp:attachment":[{"href":"https:\/\/sitepourvtc.com\/wp-json\/wp\/v2\/media?parent=12672"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}