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 /*
  * Interface to calculation of the Fermi density effect as per the method
  * described in:
  *
  *   R. M. Sternheimer, M. J. Berger, and S. M. Seltzer. Density
  *   effect for the ionization loss of charged particles in various sub-
  *   stances. Atom. Data Nucl. Data Tabl., 30:261, 1984.
  *
  * Which (among other Sternheimer references) builds on:
  *
  *   R. M. Sternheimer. The density effect for ionization loss in
  *   materials. Phys. Rev., 88:851­859, 1952.
  *
  * The returned values of delta are directly from the Sternheimer calculation,
  * and not Sternheimer's popular three-part approximate parameterization
  * introduced in the same paper.
  *
  * Author: Matthew Strait <straitm@umn.edu> 2019
  */
 
 #ifndef G4DensityEffectCalculator_HH
 #define G4DensityEffectCalculator_HH
 
 #include "globals.hh"
 
 class G4Material;
 
 class G4DensityEffectCalculator
 {
  public:
   G4DensityEffectCalculator(const G4Material*, G4int);
   ~G4DensityEffectCalculator();
 
   // The Sternheimer 'x' defined as log10(p/m) == log10(beta*gamma).
   G4double ComputeDensityCorrection(G4double x);
 
  private:
   /*
    * Given a material defined in 'par' with a plasma energy, mean excitation
    * energy, and set of atomic energy levels ("oscillator frequencies") with
    * occupation fractions ("oscillation strengths"), solve for the Sternheimer
    * adjustment factor (Sternheimer 1984 eq 8) and record (into 'par') the values
    * of the adjusted oscillator frequencies and Sternheimer constants l_i.
    * After doing this, 'par' is ready for a calculation of delta for an
    * arbitrary particle energy.  Returns true on success, false on failure.
    */
   G4double FermiDeltaCalculation(G4double x);
 
   G4double Newton(G4double x0, G4bool first);
 
   G4double DFRho(G4double);
 
   G4double FRho(G4double);
 
   G4double DEll(G4double);
 
   G4double Ell(G4double);
 
   G4double DeltaOnceSolved(G4double);
 
   const G4Material* fMaterial;
   G4int fVerbose{0};
   G4int fWarnings{0};
 
   // Number of energy levels.  If a single element, this is the number
   // of subshells.  If several elements, this is the sum of the number
   // of subshells.  In principle, could include levels for molecular
   // orbitals or other non-atomic states.  The last level is always
   // the conduction band.  If the material is an insulator, set the
   // oscillator strength for that level to zero and the energy to
   // any value.
   const G4int nlev;
 
   G4double fConductivity;
 
   // Current Sternheimer 'x' defined as log10(p/m) == log10(beta*gamma).
   G4double sternx;
 
   // The plasma energy of the material in eV, which is simply
   // 28.816 sqrt(density Z/A), with density in g/cc.
   G4double plasmaE;
 
   // The mean excitation energy of the material in eV, i.e. the 'I' in the
   // Bethe energy loss formula.
   G4double meanexcite;
 
   // Sternheimer's "oscillator strengths", which are simply the fraction
   // of electrons in a given energy level.  For a single element, this is
   // the fraction of electrons in a subshell.  For a compound or mixture,
   // it is weighted by the number fraction of electrons contributed by
   // each element, e.g. for water, oxygen's electrons are given 8/10 of the
   // weight.
   G4double* sternf;
 
   // Energy levels.  Can be found for free atoms in, e.g., T. A. Carlson.
   // Photoelectron and Auger Spectroscopy. Plenum Press, New York and London,
   // 1985. Available in a convenient form in G4AtomicShells.cc.
   //
   // Sternheimer 1984 implies that the energy level for conduction electrons
   // (the final element of this array) should be set to zero, although the
   // computation could be run with other values.
   G4double* levE;
 
   /***** Results of intermediate calculations *****/
 
   // The Sternheimer parameters l_i which appear in Sternheimer 1984 eq(1).
   G4double* sternl;
 
   // The adjusted energy levels, as found using Sternheimer 1984 eq(8).
   G4double* sternEbar;
 };
 
 #endif

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