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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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