| 1 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>5.6. Physics Table</title><link rel="stylesheet" href="../xml/XSLCustomizationLayer/G4HTMLStylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.1"><link rel="start" href="index.html" title="Geant4 User's Guide for Application Developers"><link rel="up" href="ch05.html" title="Chapter 5. Tracking and Physics"><link rel="prev" href="ch05s05.html" title="5.5. Cuts per Region"><link rel="next" href="ch05s07.html" title="5.7. User Limits"><script language="JavaScript">
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| 8 | </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">5.6.
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| 9 | Physics Table
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| 10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch05s05.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center">Chapter 5.
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| 11 | Tracking and Physics
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| 12 | </th><td width="20%" align="right"> <a accesskey="n" href="ch05s07.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sect.PhysTab"></a>5.6.
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| 13 | Physics Table
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| 14 | </h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.PhysTab.Gene"></a>5.6.1.
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| 15 | General Concepts
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| 16 | </h3></div></div></div><p>
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| 17 | In Geant4, physics processes use many tables of cross sections,
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| 18 | energy losses and other physics values. Before the execution of an
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| 19 | event loop, the <code class="literal">BuildPhysicsTable()</code> method of
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| 20 | <span class="emphasis"><em>G4VProcess</em></span> is invoked for all processes and
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| 21 | cross section tables are prepared. "Standard" electromagnetic
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| 22 | processes calculate cross section and/or energy loss values for
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| 23 | each material and for each production cut value assigned to each
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| 24 | material. A change in production cut values therefore require these
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| 25 | cross sections to be re-calculated. Cross sections for hadronic
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| 26 | processes do not depend on the production cut.
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| 27 | </p><p>
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| 28 | The <span class="emphasis"><em>G4PhysicsTable</em></span> class is used to handle cross section
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| 29 | tables. <span class="emphasis"><em>G4PhysicsTable</em></span> is a collection of instances of
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| 30 | <span class="emphasis"><em>G4PhysicsVector</em></span> (and derived classes), each of which has
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| 31 | cross section values for a particle within a given energy range
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| 32 | traveling in a material.
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| 33 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.PhysTab.MateCoup"></a>5.6.2.
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| 34 | Material-Cuts Couple
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| 35 | </h3></div></div></div><p>
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| 36 | Users can assign different production cuts to different regions
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| 37 | (see <a href="ch05s05.html" title="5.5.
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| 38 | Cuts per Region
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| 39 | ">Section 5.5</a>).
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| 40 | This means that if the same material is used in regions with different
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| 41 | cut values, the processes need to prepare several different cross
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| 42 | sections for that material.
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| 43 | </p><p>
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| 44 | The <span class="emphasis"><em>G4ProductionCutsTable</em></span> has
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| 45 | <span class="emphasis"><em>G4MaterialCutsCouple</em></span>
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| 46 | objects, each of which consists of a material paired with a cut
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| 47 | value. These <span class="emphasis"><em>G4MaterialCutsCouple</em></span>s are numbered with an
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| 48 | index which is the same as the index of a <span class="emphasis"><em>G4PhysicsVector</em></span>
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| 49 | for the corresponding <span class="emphasis"><em>G4MaterialCutsCouple</em></span>in the
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| 50 | <span class="emphasis"><em>G4PhysicsTable</em></span>. The list of
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| 51 | <span class="emphasis"><em>MaterialCutsCouple</em></span>s used
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| 52 | in the current geometry setup is updated before starting the event
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| 53 | loop in each run.
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| 54 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.PhysTab.Fio"></a>5.6.3.
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| 55 | File I/O for the Physics Table
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| 56 | </h3></div></div></div><p>
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| 57 | Calculated physics tables for "Standard" electromagnetic processes
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| 58 | can be stored in files. The user may thus eliminate the time
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| 59 | required for the calculation of physics tables by retrieving them
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| 60 | from the files.
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| 61 | </p><p>
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| 62 | Using the built-in user command "<span class="bold"><strong>storePhysicsTable</strong></span>"
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| 63 | (see <a href="ch07.html#sect.BuiltinCom" title="7.1.
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| 64 | Built-in Commands
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| 65 | ">Section 7.1</a>),
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| 66 | stores physics tables in files. Information on materials and
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| 67 | cuts defined in the current geometry setup are stored together with
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| 68 | physics tables because calculated values in the physics tables
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| 69 | depend on <span class="emphasis"><em>MaterialCutsCouple</em></span>. Note that physics tables are
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| 70 | calculated before the event loop, not in the initialization phase.
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| 71 | So, at least one event must be executed before using the
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| 72 | "<span class="bold"><strong>storePhysicsTable</strong></span>" command.
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| 73 | </p><p>
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| 74 | Calculated physics tables can be retrieved from files by using
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| 75 | the "<span class="bold"><strong>retrievePhysicsTable</strong></span>" command. Materials
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| 76 | and cuts from files are compared with those defined in the current geometry
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| 77 | setup, and only physics vectors corresponding to the
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| 78 | <span class="emphasis"><em>MaterialCutsCouple</em></span>s used in the current setup are restored.
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| 79 | Note that nothing happens just after the
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| 80 | "<span class="bold"><strong>retrievePhysicsTable</strong></span>" command is issued.
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| 81 | Restoration of physics tables will be executed in parallel with the calculation
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| 82 | of physics tables.
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| 83 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.PhysTab.Build"></a>5.6.4.
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| 84 | Building the Physics Table
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| 85 | </h3></div></div></div><p>
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| 86 | In the <code class="literal">G4RunManagerKernel::RunInitialization()</code> method,
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| 87 | after the list of <span class="emphasis"><em>MaterialCutsCouple</em></span>s is updated, the
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| 88 | <code class="literal">G4VUserPhysicsList::BuildPhysicsTable()</code> method is invoked
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| 89 | to build physics tables for all processes.
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| 90 | </p><p>
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| 91 | Initially, the <code class="literal">G4VProcess::PreparePhysicsTable()</code> method
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| 92 | is invoked. Each process creates <span class="emphasis"><em>G4PhysicsTable</em></span> objects as
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| 93 | necessary. It then checks whether the <span class="emphasis"><em>MaterialCutsCouple</em></span>s
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| 94 | have been modified after a run to determine if the corresponding
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| 95 | physics vectors can be used in the next run or need to be
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| 96 | re-calculated.
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| 97 | </p><p>
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| 98 | Next, the <code class="literal">G4VProcess::RetrievePhysicsTable()</code> method is
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| 99 | invoked if the <code class="literal">G4VUserPhysicsList::fRetrievePhysicsTable</code>
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| 100 | flag is asserted. After checking materials and cuts in files,
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| 101 | physics vectors corresponding to the <span class="emphasis"><em>MaterialCutsCouple</em></span>s
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| 102 | used in the current setup are restored.
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| 103 | </p><p>
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| 104 | Finally, the <code class="literal">G4VProcess::BuildPhysicsTable()</code> method is
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| 105 | invoked and only physics vectors which need to be re-calculated are
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| 106 | built.
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| 107 | </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch05s05.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"><a accesskey="u" href="ch05.html"><img src="AllResources/IconsGIF/up.gif" alt="Up"></a></td><td width="40%" align="right"> <a accesskey="n" href="ch05s07.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">5.5.
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| 108 | Cuts per Region
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| 109 | </td><td width="20%" align="center"><a accesskey="h" href="index.html"><img src="AllResources/IconsGIF/home.gif" alt="Home"></a></td><td width="40%" align="right" valign="top"> 5.7.
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| 110 | User Limits
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| 111 | </td></tr></table></div></body></html>
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