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8 | <!-- Changed by: Katsuya Amako, 14-Jul-1998 --> |
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9 | <!-- Proof read by: Joe Chuma, 29-Jun-1999 --> |
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10 | |
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11 | <TABLE WIDTH="100%" > |
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12 | <TR> |
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13 | <TD> |
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14 | </A> |
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15 | <A HREF="index.html"> |
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16 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents" HEIGHT=16 WIDTH=59></A> |
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17 | <A HREF="geometry.html"> |
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21 | </TD> |
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22 | |
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23 | <TD ALIGN="Right"><FONT COLOR="#238E23"><FONT SIZE=-1> |
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24 | <B>Geant4 User's Guide</B> <BR> |
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25 | <B>For Application Developers</B> <BR> |
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26 | <B>Detector Definition and Response</B> </FONT></FONT> </TD> |
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27 | </TR> |
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28 | </TABLE> |
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29 | <P><BR> |
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30 | |
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31 | <CENTER><FONT COLOR="#238E23"><FONT SIZE=+3> |
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32 | <B>4.2 Material</B> </FONT></FONT> |
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33 | </CENTER> |
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34 | <BR> |
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35 | <BR> |
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36 | |
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37 | <HR ALIGN="Center" SIZE="7%"> |
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38 | <p> |
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39 | |
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40 | <a name="4.2.1"> |
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41 | <H2>4.2.1 General considerations</H2></a> |
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42 | |
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43 | In nature, materials (chemical compounds, mixtures) are made of elements, |
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44 | and elements are made of isotopes. Geant4 has three main classes |
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45 | designed to reflect this organization. Each of these classes has a table, |
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46 | which is a static data member, used to keep track of the instances of the |
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47 | respective classes created. |
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48 | <p> |
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49 | <dl><dl> |
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50 | <dt><i>G4Isotope</i> |
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51 | <dd>This class describes the properties of atoms: atomic number, number of |
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52 | nucleons, mass per mole, etc. |
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53 | </p> |
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54 | <p> |
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55 | <dt><i>G4Element</i> |
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56 | <dd>This class describes the properties of elements: effective atomic number, |
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57 | effective number of nucleons, effective mass per mole, number of isotopes, |
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58 | shell energy, and quantities like cross section per atom, etc. |
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59 | </p> |
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60 | <p> |
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61 | <dt><i>G4Material</i> |
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62 | <dd>This class describes the macroscopic properties of matter: |
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63 | density, state, temperature, pressure, and macroscopic quantities like |
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64 | radiation length, mean free path, dE/dx, etc. |
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65 | </p> |
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66 | </dl></dl> |
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67 | <p> |
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68 | Only the <i>G4Material</i> class is visible to the rest of the toolkit and |
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69 | used by the tracking, the geometry and the physics. It contains all the |
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70 | information relevant to its constituent elements and isotopes, while at |
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71 | the same time hiding their implementation details. |
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72 | </p> |
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73 | |
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74 | <hr> |
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75 | <a name="4.2.2"> |
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76 | <h2>4.2.2 Introduction to the Classes</h2></a> |
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77 | |
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78 | <b><i>G4Isotope</i></b> |
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79 | <p> |
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80 | A <i>G4Isotope</i> object has a name, atomic number, number of nucleons, mass |
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81 | per mole, and an index in the table. The constructor automatically stores |
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82 | "this" isotope in the isotopes table, which will assign it an index number. |
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83 | </p> |
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84 | <br> |
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85 | |
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86 | <b><i>G4Element</i></b> |
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87 | <p> |
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88 | A <i>G4Element</i> object has a name, symbol, effective atomic number, |
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89 | effective number of nucleons, effective mass of a mole, an index in the |
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90 | elements table, the number of isotopes, a vector of pointers to such isotopes, |
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91 | and a vector of relative abundances referring to such isotopes (where relative |
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92 | abundance means the number of atoms per volume). In addition, the class has |
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93 | methods to add, one by one, the isotopes which are to form the element. |
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94 | </p> |
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95 | <p> |
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96 | A <i>G4Element</i> object can be constructed by directly providing the |
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97 | effective atomic number, effective number of nucleons, and effective mass of |
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98 | a mole, if the user explicitly wants to do so. Alternatively, a |
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99 | <i>G4Element</i> object can be constructed by declaring the number of |
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100 | isotopes of which it will be composed. The constructor will "new" a vector |
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101 | of pointers to <i>G4Isotopes</i> and a vector of doubles to store their |
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102 | relative abundances. Finally, the method to add an isotope must be invoked |
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103 | for each of the desired (pre-existing) isotope objects, providing their |
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104 | addresses and relative abundances. At the last isotope entry, the system will |
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105 | automatically compute the effective atomic number, effective number of |
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106 | nucleons and effective mass of a mole, and will store "this" element in the |
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107 | elements table. |
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108 | </p> |
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109 | <p> |
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110 | A few quantities, with physical meaning or not, which are constant in |
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111 | a given element, are computed and stored here as "derived data members". |
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112 | </p> |
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113 | <p> |
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114 | Using the internal Geant4 database, a G4Element can be accessed by atomic |
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115 | number or by atomic symbol ("Al", "Fe", "Pb"...). In that case |
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116 | G4Element will be found from the list of existing elements or |
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117 | will be constructed using data from the Geant4 database, which is derived |
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118 | from the NIST database of elements and isotope compositions |
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119 | (http://physics.nist.gov/PhysRefData/Compositions/index.html). Thus, |
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120 | the natural isotope composition can be built by default. The same element |
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121 | can be created as using the NIST database with natural composition of isotopes |
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122 | and from scratch in user code with user defined isotope composition. |
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123 | </p> |
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124 | <br> |
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125 | |
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126 | <b><i>G4Material</i></b> |
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127 | <p> |
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128 | A <i>G4Material</i> object has a name, density, physical state, temperature |
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129 | and pressure (by default the standard conditions), the number of elements and |
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130 | a vector of pointers to such elements, a vector of the fraction of mass for |
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131 | each element, a vector of the atoms (or molecules) numbers of each element, |
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132 | and an index in the materials table. In addition, the class has methods to |
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133 | add, one by one, the elements which will comprise the material. |
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134 | </p> |
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135 | <p> |
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136 | A <i>G4Material</i> object can be constructed by directly providing the |
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137 | resulting effective numbers, if the user explicitly wants to do so (an |
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138 | underlying element will be created with these numbers). Alternatively, a |
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139 | <i>G4Material</i> object can be constructed by declaring the number of |
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140 | elements of which it will be composed. The constructor will "new" a vector |
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141 | of pointers to <i>G4Element</i> and a vector of doubles to store their |
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142 | fraction of mass. Finally, the method to add an element must be invoked |
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143 | for each of the desired (pre-existing) element objects, providing their |
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144 | addresses and mass fractions. At the last element entry, the system will |
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145 | automatically compute the vector of the number of atoms of each element per |
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146 | volume, the total number of electrons per volume, and will store "this" |
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147 | material in the materials table. In the same way, a material can be |
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148 | constructed as a mixture of other materials and elements. |
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149 | </p> |
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150 | <p> |
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151 | It should be noted that if the user provides the number of atoms (or |
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152 | molecules) for each element comprising the chemical compound, the system |
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153 | automatically computes the mass fraction. A few quantities, with physical |
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154 | meaning or not, which are constant in a given material, are computed and |
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155 | stored here as "derived data members". |
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156 | </p> |
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157 | <p> |
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158 | Some materials are included in the internal Geant4 database, which |
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159 | were derived from the NIST database of material properties |
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160 | (http://physics.nist.gov/PhysRefData/Star/Text/method.html). |
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161 | Additionally a number of materials frequently used in HEP is included |
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162 | in the database. |
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163 | Materials are interrogated or constructed by their <a href="materialNames.html"> |
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164 | <i>names</a></i>. There are UI |
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165 | commands for the material category, which provide an interactive |
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166 | access to the database. If material is created using the NIST database it will |
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167 | consist of elements with natural composition of isotopes. |
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168 | </p> |
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169 | <br> |
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170 | |
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171 | <b>Final Considerations</b> |
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172 | |
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173 | The classes will automatically decide if the total of the mass fractions |
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174 | is correct, and perform the necessary checks. The main reason why a fixed |
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175 | index is kept as a data member is that many cross section and energy tables |
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176 | will be built in the physics processes "by rows of materials (or elements, |
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177 | or even isotopes)". The tracking gives the physics process the address of |
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178 | a material object (the material of the current volume). |
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179 | If the material has an index according to which the cross section table |
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180 | has been built, then direct access is available when a number in such a |
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181 | table must be accessed. We get directly to the correct row, and the energy |
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182 | of the particle will tell us the column. Without such an index, every access |
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183 | to the cross section or energy tables would imply a search to get to the |
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184 | correct material's row. More details will be given in the section on |
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185 | processes. |
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186 | </p> |
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187 | <br> |
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188 | |
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189 | <hr> |
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190 | <a name="4.2.3"> |
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191 | <h2>4.2.3 Recipes for Building Elements and Materials</h2></a> |
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192 | |
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193 | Source listing 4.2.1 illustrates the different ways to define materials. |
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194 | <p> |
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195 | <center> |
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196 | <table border=2 cellpadding=10> |
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197 | <tr> |
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198 | <td> |
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199 | <PRE> |
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200 | #include "G4Isotope.hh" |
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201 | #include "G4Element.hh" |
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202 | #include "G4Material.hh" |
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203 | #include "G4UnitsTable.hh" |
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204 | |
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205 | int main() { |
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206 | |
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207 | G4String name, symbol; // a=mass of a mole; |
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208 | G4double a, z, density; // z=mean number of protons; |
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209 | G4int iz, n; //iz=nb of protons in an isotope; |
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210 | // n=nb of nucleons in an isotope; |
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211 | |
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212 | G4int ncomponents, natoms; |
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213 | G4double abundance, fractionmass; |
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214 | G4double temperature, pressure; |
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215 | |
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216 | G4UnitDefinition::BuildUnitsTable(); |
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217 | |
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218 | // |
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219 | // define Elements |
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220 | // |
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221 | |
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222 | a = 1.01*g/mole; |
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223 | G4Element* elH = new G4Element(name="Hydrogen",symbol="H" , z= 1., a); |
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224 | |
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225 | a = 12.01*g/mole; |
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226 | G4Element* elC = new G4Element(name="Carbon" ,symbol="C" , z= 6., a); |
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227 | |
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228 | a = 14.01*g/mole; |
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229 | G4Element* elN = new G4Element(name="Nitrogen",symbol="N" , z= 7., a); |
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230 | |
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231 | a = 16.00*g/mole; |
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232 | G4Element* elO = new G4Element(name="Oxygen" ,symbol="O" , z= 8., a); |
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233 | |
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234 | a = 28.09*g/mole; |
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235 | G4Element* elSi = new G4Element(name="Silicon", symbol="Si", z=14., a); |
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236 | |
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237 | a = 55.85*g/mole; |
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238 | G4Element* elFe = new G4Element(name="Iron" ,symbol="Fe", z=26., a); |
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239 | |
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240 | a = 183.84*g/mole; |
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241 | G4Element* elW = new G4Element(name="Tungsten" ,symbol="W", z=74., a); |
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242 | |
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243 | a = 207.20*g/mole; |
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244 | G4Element* elPb = new G4Element(name="Lead" ,symbol="Pb", z=82., a); |
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245 | |
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246 | // |
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247 | // define an Element from isotopes, by relative abundance |
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248 | // |
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249 | |
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250 | G4Isotope* U5 = new G4Isotope(name="U235", iz=92, n=235, a=235.01*g/mole); |
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251 | G4Isotope* U8 = new G4Isotope(name="U238", iz=92, n=238, a=238.03*g/mole); |
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252 | |
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253 | G4Element* elU = new G4Element(name="enriched Uranium", symbol="U", ncomponents=2); |
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254 | elU->AddIsotope(U5, abundance= 90.*perCent); |
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255 | elU->AddIsotope(U8, abundance= 10.*perCent); |
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256 | |
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257 | |
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258 | cout << *(G4Isotope::GetIsotopeTable()) << endl; |
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259 | |
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260 | cout << *(G4Element::GetElementTable()) << endl; |
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261 | |
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262 | // |
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263 | // define simple materials |
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264 | // |
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265 | |
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266 | density = 2.700*g/cm3; |
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267 | a = 26.98*g/mole; |
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268 | G4Material* Al = new G4Material(name="Aluminum", z=13., a, density); |
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269 | |
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270 | density = 1.390*g/cm3; |
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271 | a = 39.95*g/mole; |
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272 | G4Material* lAr = new G4Material(name="liquidArgon", z=18., a, density); |
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273 | |
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274 | density = 8.960*g/cm3; |
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275 | a = 63.55*g/mole; |
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276 | G4Material* Cu = new G4Material(name="Copper" , z=29., a, density); |
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277 | |
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278 | // |
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279 | // define a material from elements. case 1: chemical molecule |
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280 | // |
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281 | |
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282 | density = 1.000*g/cm3; |
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283 | G4Material* H2O = new G4Material(name="Water", density, ncomponents=2); |
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284 | H2O->AddElement(elH, natoms=2); |
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285 | H2O->AddElement(elO, natoms=1); |
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286 | |
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287 | density = 1.032*g/cm3; |
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288 | G4Material* Sci = new G4Material(name="Scintillator", density, ncomponents=2); |
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289 | Sci->AddElement(elC, natoms=9); |
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290 | Sci->AddElement(elH, natoms=10); |
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291 | |
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292 | density = 2.200*g/cm3; |
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293 | G4Material* SiO2 = new G4Material(name="quartz", density, ncomponents=2); |
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294 | SiO2->AddElement(elSi, natoms=1); |
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295 | SiO2->AddElement(elO , natoms=2); |
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296 | |
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297 | density = 8.280*g/cm3; |
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298 | G4Material* PbWO4= new G4Material(name="PbWO4", density, ncomponents=3); |
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299 | PbWO4->AddElement(elO , natoms=4); |
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300 | PbWO4->AddElement(elW , natoms=1); |
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301 | PbWO4->AddElement(elPb, natoms=1); |
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302 | |
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303 | // |
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304 | // define a material from elements. case 2: mixture by fractional mass |
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305 | // |
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306 | |
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307 | density = 1.290*mg/cm3; |
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308 | G4Material* Air = new G4Material(name="Air " , density, ncomponents=2); |
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309 | Air->AddElement(elN, fractionmass=0.7); |
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310 | Air->AddElement(elO, fractionmass=0.3); |
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311 | |
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312 | // |
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313 | // define a material from elements and/or others materials (mixture of mixtures) |
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314 | // |
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315 | |
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316 | density = 0.200*g/cm3; |
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317 | G4Material* Aerog = new G4Material(name="Aerogel", density, ncomponents=3); |
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318 | Aerog->AddMaterial(SiO2, fractionmass=62.5*perCent); |
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319 | Aerog->AddMaterial(H2O , fractionmass=37.4*perCent); |
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320 | Aerog->AddElement (elC , fractionmass= 0.1*perCent); |
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321 | |
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322 | // |
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323 | // examples of gas in non STP conditions |
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324 | // |
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325 | |
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326 | density = 27.*mg/cm3; |
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327 | pressure = 50.*atmosphere; |
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328 | temperature = 325.*kelvin; |
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329 | G4Material* CO2 = new G4Material(name="Carbonic gas", density, ncomponents=2, |
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330 | kStateGas,temperature,pressure); |
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331 | CO2->AddElement(elC, natoms=1); |
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332 | CO2->AddElement(elO, natoms=2); |
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333 | |
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334 | density = 0.3*mg/cm3; |
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335 | pressure = 2.*atmosphere; |
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336 | temperature = 500.*kelvin; |
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337 | G4Material* steam = new G4Material(name="Water steam ", density, ncomponents=1, |
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338 | kStateGas,temperature,pressure); |
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339 | steam->AddMaterial(H2O, fractionmass=1.); |
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340 | |
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341 | // |
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342 | // What about vacuum ? Vacuum is an ordinary gas with very low density |
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343 | // |
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344 | |
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345 | density = universe_mean_density; //from PhysicalConstants.h |
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346 | pressure = 1.e-19*pascal; |
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347 | temperature = 0.1*kelvin; |
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348 | new G4Material(name="Galactic", z=1., a=1.01*g/mole, density, |
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349 | kStateGas,temperature,pressure); |
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350 | |
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351 | density = 1.e-5*g/cm3; |
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352 | pressure = 2.e-2*bar; |
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353 | temperature = STP_Temperature; //from PhysicalConstants.h |
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354 | G4Material* beam = new G4Material(name="Beam ", density, ncomponents=1, |
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355 | kStateGas,temperature,pressure); |
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356 | beam->AddMaterial(Air, fractionmass=1.); |
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357 | |
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358 | // |
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359 | // print the table of materials |
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360 | // |
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361 | |
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362 | G4cout << *(G4Material::GetMaterialTable()) << endl; |
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363 | |
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364 | return EXIT_SUCCESS; |
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365 | } |
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366 | </PRE> |
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367 | </td> |
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368 | </tr> |
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369 | <tr> |
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370 | <td align=center> |
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371 | Source listing 4.2.1<BR> |
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372 | A program which illustrates the different ways to define materials. |
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373 | </td> |
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374 | </tr> |
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375 | </table></center> |
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376 | <p> |
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377 | As can be seen in the later examples, a material has a state: solid (the |
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378 | default), liquid, or gas. The constructor checks the density and |
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379 | automatically sets the state to gas below a given threshold (10 mg/cm3). |
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380 | </p> |
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381 | <p> |
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382 | In the case of a gas, one may specify the temperature and pressure. The |
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383 | defaults are STP conditions defined in <tt>PhysicalConstants.hh</tt>. |
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384 | </p> |
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385 | <p> |
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386 | An element must have the number of nucleons >= number of protons >= 1. |
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387 | </p> |
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388 | <p> |
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389 | A material must have non-zero values of density, temperature and pressure. |
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390 | </p> |
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391 | <p> |
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392 | Materials can also be defined using the internal Geant4 database. |
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393 | Source listing 4.2.2 illustrates how to do this for the same materials |
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394 | used in 4.2.1. There are also UI commands which allow the database to |
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395 | be accessed. <a href="materialNames.html"> |
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396 | <i>The list of currently available material names</a></i> is extended permanently. |
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397 | </p> |
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398 | <p> |
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399 | <center> |
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400 | <table border=2 cellpadding=10> |
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401 | <tr> |
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402 | <td> |
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403 | <PRE> |
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404 | #include "globals.hh" |
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405 | #include "G4Material.hh" |
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406 | #include "G4NistManager.hh" |
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407 | |
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408 | int main() { |
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409 | |
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410 | G4NistManager* man = G4NistManager::Instance(); |
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411 | man->SetVerbose(1); |
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412 | |
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413 | // |
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414 | // define elements |
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415 | // |
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416 | |
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417 | G4Element* C = man->FindOrBuildElement("C"); |
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418 | G4Element* Pb = man->FindOrBuildMaterial("Pb"); |
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419 | |
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420 | // |
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421 | // define pure NIST materials |
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422 | // |
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423 | |
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424 | G4Material* Al = man->FindOrBuildMaterial("G4_Al"); |
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425 | G4Material* Cu = man->FindOrBuildMaterial("G4_Cu"); |
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426 | |
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427 | // |
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428 | // define NIST materials |
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429 | // |
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430 | |
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431 | G4Material* H2O = man->FindOrBuildMaterial("G4_WATER"); |
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432 | G4Material* Sci = man->FindOrBuildMaterial("G4_PLASTIC_SC_VINYLTOLUENE"); |
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433 | G4Material* SiO2 = man->FindOrBuildMaterial("G4_SILICON_DIOXIDE"); |
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434 | G4Material* Air = man->FindOrBuildMaterial("G4_AIR"); |
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435 | |
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436 | // |
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437 | // HEP materials |
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438 | // |
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439 | |
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440 | G4Material* PbWO4 = man->FindOrBuildMaterial("G4_PbWO4"); |
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441 | G4Material* lAr = man->FindOrBuildMaterial("G4_lAr"); |
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442 | G4Material* vac = man->FindOrBuildMaterial("G4_Galactic"); |
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443 | |
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444 | // |
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445 | // define gas material at non STP conditions (T = 120K, P=0.5atm) |
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446 | // |
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447 | |
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448 | G4Material* coldAr = man->ConstructNewGasdMaterial("ColdAr","G4_Ar",120.*kelvin,0.5*atmosphere); |
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449 | |
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450 | // |
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451 | // print the table of materials |
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452 | // |
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453 | |
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454 | G4cout << *(G4Material::GetMaterialTable()) << endl; |
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455 | |
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456 | return EXIT_SUCCESS; |
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457 | } |
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458 | </PRE> |
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459 | </td> |
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460 | </tr> |
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461 | <tr> |
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462 | <td align=center> |
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463 | Source listing 4.2.2<BR> |
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464 | A program which shows how to define materials from the internal database. |
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465 | </td> |
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466 | </tr> |
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467 | </table></center> |
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468 | |
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469 | <hr> |
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470 | <a name="4.2.4"> |
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471 | <h2>4.2.4 The Tables</h2></a> |
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472 | |
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473 | <b>Print a constituent</b> |
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474 | <p> |
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475 | The following shows how to print a constituent: |
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476 | |
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477 | <PRE> |
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478 | G4cout << elU << endl; |
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479 | G4cout << Air << endl; |
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480 | </PRE> |
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481 | <p> |
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482 | <b>Print the table of materials</b> |
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483 | <p> |
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484 | The following shows how to print the table of materials: |
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485 | |
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486 | <PRE> |
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487 | G4cout << *(G4Material::GetMaterialTable()) << endl; |
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488 | </PRE> |
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489 | <br> |
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490 | <br> |
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491 | |
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492 | <hr><a href="../../../../Authors/html/subjectsToAuthors.html"> |
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493 | <i>About the authors</a></i> |
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494 | </p> |
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495 | |
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496 | </BODY> |
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497 | </HTML> |
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