source: trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/GettingStarted/materialDef.xml @ 1358

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<!--  [History]                                               -->
<!--    Changed by: Katsuya Amako,  4-Aug-1998                -->
<!--    Changed by: Dennis Wright, 28-Nov-2001                -->
<!--    Proof read by: Joe Chuma,  15-Jun-1999                -->
<!--    Converted to DocBook: Katsuya Amako, Aug-2006         -->
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<!-- ******************* Section (Level#1) ****************** -->
<sect1 id="sect.HowToSpecMate">
<title>
How to Specify Materials in the Detector
</title>

<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.GeneCons">
<title>
General Considerations
</title>

<para>
In nature, general materials (chemical compounds, mixtures) are
made of elements, and elements are made of isotopes. Therefore,
these are the three main classes designed in Geant4. Each of these
classes has a table as a static data member, which is for keeping
track of the instances created of the respective classes.
</para>

<para>
The <emphasis>G4Element</emphasis> class describes the properties of the
atoms:
<itemizedlist spacing="compact">
  <listitem><para>
  atomic number,
  </para></listitem>
  <listitem><para>
  number of nucleons,
  </para></listitem>
  <listitem><para>
  atomic mass,
  </para></listitem>
  <listitem><para>
  shell energy,
  </para></listitem>
  <listitem><para>
  as well as quantities such as cross sections per atom, etc.
  </para></listitem>
</itemizedlist>
</para>

<para>
The <emphasis>G4Material</emphasis> class describes the macroscopic properties
of matter:
<itemizedlist spacing="compact">
  <listitem><para>
  density,
  </para></listitem>
  <listitem><para>
  state,
  </para></listitem>
  <listitem><para>
  temperature,
  </para></listitem>
  <listitem><para>
  pressure,
  </para></listitem>
  <listitem><para>
  as well as macroscopic quantities like radiation length, mean
  free path, dE/dx, etc.
  </para></listitem>
</itemizedlist>
</para>

<para>
The <emphasis>G4Material</emphasis> class is the one which is visible to the
rest of the toolkit, and is used by the tracking, the geometry, and
the physics. It contains all the information relative to the
eventual elements and isotopes of which it is made, at the same
time hiding the implementation details.
</para>

</sect2>

<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.DefSimpleMate">
<title>
Define a Simple Material
</title>

<para>
In the example below, liquid argon is created, by specifying its
name, density, mass per mole, and atomic number.
<example id="programlist_HowToSpecMate_1">
<title>
Creating liquid argon.
</title>
<programlisting>
  G4double density = 1.390*g/cm3;
  G4double a = 39.95*g/mole;
  G4Material* lAr = new G4Material(name="liquidArgon", z=18., a, density);
</programlisting>
</example>
</para>

<para>
The pointer to the material, <emphasis>lAr</emphasis>, will be used to specify
the matter of which a given logical volume is made:
<informalexample>
<programlisting>
  G4LogicalVolume* myLbox = new G4LogicalVolume(aBox,lAr,"Lbox",0,0,0);
</programlisting>
</informalexample>
</para>

</sect2>

<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.DefineMolecule">
<title>
Define a Molecule
</title>

<para>
In the example below, the water, <emphasis>H2O</emphasis>, is built from its
components, by specifying the number of atoms in the molecule.
<example id="programlist_HowToSpecMate_2">
<title>
Creating water by defining its molecular components.
</title>
<programlisting>
  a = 1.01*g/mole;
  G4Element* elH  = new G4Element(name="Hydrogen",symbol="H" , z= 1., a);

  a = 16.00*g/mole;
  G4Element* elO  = new G4Element(name="Oxygen"  ,symbol="O" , z= 8., a);

  density = 1.000*g/cm3;
  G4Material* H2O = new G4Material(name="Water",density,ncomponents=2);
  H2O-&gt;AddElement(elH, natoms=2);
  H2O-&gt;AddElement(elO, natoms=1);
</programlisting>
</example>
</para>

</sect2>

<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.DefMixtureByFractionalMass">
<title>
Define a Mixture by Fractional Mass
</title>

<para>
In the example below, air is built from nitrogen and oxygen, by
giving the fractional mass of each component.

<example id="programlist_HowToSpecMate_3">
<title>
Creating air by defining the fractional mass of its components.
</title>
<programlisting>
  a = 14.01*g/mole;
  G4Element* elN  = new G4Element(name="Nitrogen",symbol="N" , z= 7., a);

  a = 16.00*g/mole;
  G4Element* elO  = new G4Element(name="Oxygen"  ,symbol="O" , z= 8., a);

  density = 1.290*mg/cm3;
  G4Material* Air = new G4Material(name="Air  ",density,ncomponents=2);
  Air-&gt;AddElement(elN, fractionmass=70*perCent);
  Air-&gt;AddElement(elO, fractionmass=30*perCent);
</programlisting>
</example>
</para>

</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.DefMateFromDatabase">
<title>
Define a Material from the Geant4 Material Database
</title>

<para>
In the example below, air and water are accessed via the Geant4
material database.
<example id="programlist_HowToSpecMate_4">
<title>
Defining air and water from the internal Geant4 database.
</title>
<programlisting>
  G4NistManager* man = G4NistManager::Instance();

  G4Material* H2O  = man-&gt;FindOrBuildMaterial("G4_WATER");
  G4Material* Air  = man-&gt;FindOrBuildMaterial("G4_AIR");
</programlisting>
</example>
</para>

</sect2>

<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.HowToSpecMate.PrintMateInfo">
<title>
Print Material Information
</title>

<para>
<example id="programlist_HowToSpecMate_5">
<title>
Printing information about materials.
</title>
<programlisting>
  G4cout &lt;&lt; H2O;                                \\ print a given material
  G4cout &lt;&lt; *(G4Material::GetMaterialTable());  \\ print the list of materials
</programlisting>
</example>

In <literal>examples/novice/N03/N03DetectorConstruction.cc</literal>, you
will find examples of all possible ways to build a material.
</para>


</sect2>
</sect1>