include/Geant4/G4AtomicFormFactor.hh

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0025
0026 //---------------------------------------------------------------------------
0027 //
0028 // ClassName:   G4AtomicFormFactor
0029 //
0030 // Description: Contains the function for the evaluation of the atomic form
0031 //              factor. The tabulated data are available on IUCr website
0032 //
0033 // Class description:
0034 //
0035 // XXX
0036 //
0037 // 21-04-16, created by E.Bagli
0038
0039 #ifndef G4ATOMICFORMFACTOR_HH
0040 #define G4ATOMICFORMFACTOR_HH 1
0041
0042 #include "G4Exp.hh"
0043 #include <CLHEP/Units/PhysicalConstants.h>
0044 #include "globals.hh"
0045
0046 #include <map>
0047 #include <vector>
0048
0049 class G4AtomicFormFactor
0050 {
0051  public:
0052   static G4AtomicFormFactor* GetManager()
0053   {
0054     if (s_G4AtomicFormFactorManager == nullptr) {
0055       s_G4AtomicFormFactorManager = new G4AtomicFormFactor();
0056     }
0057     return s_G4AtomicFormFactorManager;
0058   }
0059
0060   G4double Get(G4double kScatteringVector, G4int Z, G4int charge = 0)
0061   {
0062     if (loadedIndex != GetIndex(Z, charge)) {
0063       LoadCoefficiencts(GetIndex(Z, charge));
0064     }
0065     G4double result = 0.;
0066     // Convert k from mm^-1 to Å^-1 and divide by 4π , then square.
0067     const G4double kVecOn4Pi = (kScatteringVector * 1.0e-7) * (1.0 / (4.0 * CLHEP::pi));
0068     G4double kVecOn4PiSquared = kVecOn4Pi * kVecOn4Pi;  // (k/(4π))^2 in Å^-2
0069
0070     for (unsigned int i0 = 0; i0 < 4; i0++) {
0071       result += theCoefficients[i0 * 2] * G4Exp(-theCoefficients[i0 * 2 + 1] * kVecOn4PiSquared);
0072     }
0073     result += theCoefficients[8];
0074     return result;
0075   }
0076
0077  protected:
0078   G4AtomicFormFactor();
0079   ~G4AtomicFormFactor() = default;
0080
0081  private:
0082   void InsertCoefficients(G4int index, const std::vector<G4double>& aDoubleVec)
0083   {
0084     theCoefficientsMap.insert(std::pair<G4int, std::vector<G4double>>(index, aDoubleVec));
0085   }
0086
0087   // LoadCoefficiencts() method allows the evaluation of the atomic form
0088   // factor coefficients and the storage in theCoefficients.
0089   // If theCoefficients are already correct, no need to get new ones
0090   // Reference: International Tables for Crystallography (2006).
0091   // Vol. C, ch. 6.1, pp. 554-595
0092   // doi: 10.1107/97809553602060000600
0093   // Chapter 6.1. Intensity of diffracted intensities
0094   // IUCr Eq. 6.1.1.15, Coefficients Table 6.1.1.4
0095   void LoadCoefficiencts(G4int index)
0096   {
0097     loadedIndex = index;
0098     for (unsigned int i0 = 0; i0 < 9; i0++) {
0099       theCoefficients[i0] = theCoefficientsMap[index][i0];
0100     }
0101   }
0102
0103   // Get() function gives back the Atomic Form Factor of the Z material
0104   inline G4int GetIndex(G4int Z, G4int charge = 0) { return Z * 100 + charge; }
0105
0106  private:
0107   inline static G4AtomicFormFactor* s_G4AtomicFormFactorManager = nullptr;
0108
0109   // theCoefficientsMap stores the coefficients for the form factor
0110   // calculations. It can be loaded only by LoadCoefficiencts()
0111   // and accessed by theCoefficients[].
0112   std::map<G4int, std::vector<G4double>> theCoefficientsMap;
0113   G4double theCoefficients[9];
0114   G4int loadedIndex;
0115 };
0116 #endif