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| 2 | <TITLE>
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| 3 | </TITLE>
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| 4 | <!-- Changed by: Katsuya Amako, 4-Aug-1998 -->
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| 5 | <!-- Changed by: Dennis Wright, 28-Nov-2001 -->
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| 6 | <!-- Proof read by: Joe Chuma, 15-Jun-1999 -->
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| 7 |
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| 8 | <BODY>
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| 9 | <TABLE WIDTH="100%"><TR>
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| 10 | <TD>
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| 11 |
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| 12 |
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| 13 | <A HREF="index.html">
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| 14 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents"></A>
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| 15 | <A HREF="geometryDef.html">
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| 16 | <IMG SRC="../../../../resources/html/IconsGIF/Previous.gif" ALT="Previous">
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| 17 | <A HREF="particleDef.html">
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| 18 | <IMG SRC="../../../../resources/html/IconsGIF/Next.gif" ALT="Next"></A>
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| 19 | </TD>
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| 20 | <TD ALIGN="Right">
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| 21 | <FONT SIZE="-1" COLOR="#238E23">
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| 22 | <B>Geant4 User's Guide</B>
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| 23 | <BR>
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| 24 | <B>For Application Developers</B>
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| 25 | <BR>
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| 26 | <B>Getting Started with Geant4</B>
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| 27 | </FONT>
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| 28 | </TD>
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| 29 | </TR></TABLE>
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| 30 | <BR>
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| 31 |
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| 32 | <P ALIGN="Center">
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| 33 | <FONT SIZE="+3" COLOR="#238E23">
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| 34 | <B>2.3 How to Specify Materials in the Detector</B>
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| 35 | </FONT>
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| 36 | <P><BR>
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| 37 |
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| 38 | <HR ALIGN="Center" SIZE="7%">
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| 39 | <p>
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| 40 |
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| 41 | <a name="2.3.1">
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| 42 | <H2>2.3.1 General Considerations</H2></a>
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| 43 |
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| 44 | In nature, general materials (chemical compounds, mixtures) are made of
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| 45 | elements, and elements are made of isotopes.
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| 46 | Therefore, these are the three main classes designed in Geant4.
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| 47 | Each of these classes has a table as a static data member,
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| 48 | which is for keeping track of the instances created of the respective
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| 49 | classes.
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| 50 | <P>
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| 51 | The <i>G4Element</i> class describes the properties of the atoms:
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| 52 | <ul>
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| 53 | <li>atomic number,
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| 54 | <li>number of nucleons,
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| 55 | <li>atomic mass,
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| 56 | <li>shell energy,
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| 57 | <li>as well as quantities such as cross sections per atom, etc.
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| 58 | </ul>
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| 59 | <P>
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| 60 | The <i>G4Material</i> class describes the macroscopic properties of matter:
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| 61 | <ul>
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| 62 | <li>density,
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| 63 | <li>state,
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| 64 | <li>temperature,
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| 65 | <li>pressure,
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| 66 | <li>as well as macroscopic quantities like radiation length, mean free path, dE/dx, etc.
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| 67 | </ul>
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| 68 | <P>
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| 69 | The <i>G4Material</i> class is the one which is visible to the rest
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| 70 | of the toolkit, and is used by the tracking, the geometry, and
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| 71 | the physics. It contains all the information relative to
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| 72 | the eventual elements and isotopes of which it is made, at the same time hiding
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| 73 | the implementation details.
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| 74 | <P>
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| 75 |
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| 76 | <HR>
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| 77 | <a name="2.3.2">
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| 78 | <H2>2.3.2 Define a Simple Material</H2></a>
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| 79 |
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| 80 | In the example below, liquid argon is created, by specifying its name,
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| 81 | density, mass per mole, and atomic number.
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| 82 | <P>
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| 83 | <center>
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| 84 | <table border=2 cellpadding=10>
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| 85 | <tr>
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| 86 | <td>
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| 87 | <PRE>
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| 88 | G4double density = 1.390*g/cm3;
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| 89 | G4double a = 39.95*g/mole;
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| 90 | G4Material* lAr = new G4Material(name="liquidArgon", z=18., a, density);
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| 91 | </PRE>
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| 92 | </td>
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| 93 | </tr>
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| 94 | <tr>
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| 95 | <td align=center>
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| 96 | Source listing 2.3.1<BR>
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| 97 | Creating liquid argon.
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| 98 | </td>
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| 99 | </tr>
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| 100 | </table></center>
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| 101 | <p>
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| 102 | The pointer to the material, <i>lAr</i>, will be used to specify the matter of which
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| 103 | a given logical volume is made:
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| 104 | <P>
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| 105 | <PRE>
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| 106 | G4LogicalVolume* myLbox = new G4LogicalVolume(aBox,lAr,"Lbox",0,0,0);
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| 107 | </PRE>
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| 108 | <P>
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| 109 |
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| 110 | <HR>
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| 111 | <a name="2.3.3">
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| 112 | <H2>2.3.3 Define a Molecule</H2></a>
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| 113 |
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| 114 | In the example below, the water, <i>H2O</i>, is built from its components,
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| 115 | by specifying the number of atoms in the molecule.
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| 116 | <P>
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| 117 | <center>
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| 118 | <table border=2 cellpadding=10>
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| 119 | <tr>
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| 120 | <td>
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| 121 | <PRE>
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| 122 | a = 1.01*g/mole;
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| 123 | G4Element* elH = new G4Element(name="Hydrogen",symbol="H" , z= 1., a);
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| 124 |
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| 125 | a = 16.00*g/mole;
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| 126 | G4Element* elO = new G4Element(name="Oxygen" ,symbol="O" , z= 8., a);
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| 127 |
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| 128 | density = 1.000*g/cm3;
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| 129 | G4Material* H2O = new G4Material(name="Water",density,ncomponents=2);
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| 130 | H2O->AddElement(elH, natoms=2);
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| 131 | H2O->AddElement(elO, natoms=1);
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| 132 | </PRE>
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| 133 | </td>
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| 134 | </tr>
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| 135 | <tr>
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| 136 | <td align=center>
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| 137 | Source listing 2.3.2<BR>
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| 138 | Creating water by defining its molecular components.
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| 139 | </td>
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| 140 | </tr>
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| 141 | </table></center>
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| 142 | <P>
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| 143 |
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| 144 | <HR>
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| 145 | <a name+"2.3.4">
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| 146 | <H2>2.3.4 Define a Mixture by Fractional Mass</H2></a>
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| 147 |
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| 148 | In the example below, air is built from nitrogen and oxygen, by giving the
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| 149 | fractional mass of each component.
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| 150 | <P>
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| 151 | <center>
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| 152 | <table border=2 cellpadding=10>
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| 153 | <tr>
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| 154 | <td>
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| 155 | <PRE>
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| 156 | a = 14.01*g/mole;
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| 157 | G4Element* elN = new G4Element(name="Nitrogen",symbol="N" , z= 7., a);
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| 158 |
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| 159 | a = 16.00*g/mole;
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| 160 | G4Element* elO = new G4Element(name="Oxygen" ,symbol="O" , z= 8., a);
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| 161 |
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| 162 | density = 1.290*mg/cm3;
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| 163 | G4Material* Air = new G4Material(name="Air ",density,ncomponents=2);
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| 164 | Air->AddElement(elN, fractionmass=70*perCent);
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| 165 | Air->AddElement(elO, fractionmass=30*perCent);
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| 166 | </PRE>
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| 167 | </td>
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| 168 | </tr>
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| 169 | <tr>
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| 170 | <td align=center>
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| 171 | Source listing 2.3.3<BR>
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| 172 | Creating air by defining the fractional mass of its components.
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| 173 | </td>
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| 174 | </tr>
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| 175 | </table></center>
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| 176 | <P>
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| 177 |
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| 178 | <HR>
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| 179 | <a name+"2.3.5">
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| 180 | <H2>2.3.5 Define a Material from the Geant4 Material Database</H2></a>
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| 181 |
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| 182 | In the example below, air and water are accessed via the Geant4 material database.
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| 183 | <P>
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| 184 | <center>
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| 185 | <table border=2 cellpadding=10>
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| 186 | <tr>
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| 187 | <td>
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| 188 | <PRE>
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| 189 |
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| 190 | G4NistManager* man = G4NistManager::Instance();
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| 191 |
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| 192 | G4Material* H2O = man->FindOrBuildMaterial("G4_WATER");
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| 193 | G4Material* Air = man->FindOrBuildMaterial("G4_AIR");
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| 194 |
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| 195 | </PRE>
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| 196 | </td>
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| 197 | </tr>
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| 198 | <tr>
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| 199 | <td align=center>
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| 200 | Source listing 2.3.4<BR>
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| 201 | Defining air and water from the internal Geant4 database.
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| 202 | </td>
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| 203 | </tr>
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| 204 | </table></center>
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| 205 | <P>
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| 206 |
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| 207 | <HR>
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| 208 | <a name="2.3.6">
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| 209 | <H2>2.3.6 Print Material Information</H2></a>
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| 210 |
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| 211 | <center>
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| 212 | <table border=2 cellpadding=10>
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| 213 | <tr>
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| 214 | <td>
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| 215 | <PRE>
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| 216 | G4cout << H2O; \\ print a given material
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| 217 | G4cout << *(G4Material::GetMaterialTable()); \\ print the list of materials
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| 218 | </PRE>
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| 219 | </td>
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| 220 | </tr>
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| 221 | <tr>
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| 222 | <td align=center>
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| 223 | Source listing 2.3.5<BR>
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| 224 | Printing information about materials.
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| 225 | </td>
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| 226 | </tr>
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| 227 | </table></center>
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| 228 | <P>
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| 229 | In <tt>examples/novice/N03/N03DetectorConstruction.cc</tt>, you will
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| 230 | find examples of all possible ways to build a material.
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| 231 | <P>
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| 232 |
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| 233 | <HR>
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| 234 | <A HREF="../../../../Authors/html/subjectsToAuthors.html">
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| 235 | <I>About the authors</I></A>
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| 236 |
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| 237 | </BODY>
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| 238 | </HTML>
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