NestAlg.cxx

Go to the documentation of this file.

#define AVO 6.022e23 //Avogadro's number (#/mol)
#define EMASS 9.109e-31*CLHEP::kg
#define MillerDriftSpeed true

#define GASGAP 0.25*CLHEP::cm //S2 generation region
#define BORDER 0*CLHEP::cm //liquid-gas border z-coordinate

#define QE_EFF 1 //a base or maximum quantum efficiency
#define phe_per_e 1 //S2 gain for quick studies

// different field regions, for gamma-X studies
#define WIN 0*CLHEP::mm //top Cu block (also, quartz window)
#define TOP 0 //top grid wires
#define ANE 0 //anode mesh
#define SRF 0 //liquid-gas interface
#define GAT 0 //gate grid
#define CTH 0 //cathode grid
#define BOT 0 //bottom PMT grid
#define PMT 0 //bottom Cu block and PMTs
#define MIN_ENE -1*CLHEP::eV //lets you turn NEST off BELOW a certain energy
#define MAX_ENE 1.*CLHEP::TeV //lets you turn NEST off ABOVE a certain energy
#define HIENLIM 5*CLHEP::MeV //energy at which Doke model used exclusively
#define R_TOL 0.2*CLHEP::mm //tolerance (for edge events)
#define R_MAX 1*CLHEP::km //for corraling diffusing electrons
#define Density_LXe 2.9 //reference density for density-dep. effects
#define Density_LAr 1.393
#define Density_LNe 1.207
#define Density_LKr 2.413

#include "Geant4/G4Ions.hh"
#include "Geant4/G4OpticalPhoton.hh"
#include "Geant4/G4VProcess.hh"

#include "larsim/LegacyLArG4/NestAlg.h"
#include "larsim/LegacyLArG4/G4ThermalElectron.hh"

#include "CLHEP/Random/RandGauss.h"
#include "CLHEP/Random/RandFlat.h"

G4bool diffusion = true;

G4bool SinglePhase=false, ThomasImelTail=true, OutElectrons=true;

G4double biExc = 0.77; //for alpha particles (bi-excitonic collisions)

//----------------------------------------------------------------------------
// Default constructor will return no photons or electrons unless the set
// methods are called.
NestAlg::NestAlg(CLHEP::HepRandomEngine& engine)
  : fYieldFactor(0)
  , fExcitationRatio(0)
  , fNumScintPhotons(0)
  , fNumIonElectrons(0)
  , fEnergyDep(0.)
  , fEngine(engine)
{
  fElementPropInit[2] = false;
  fElementPropInit[10] = false;
  fElementPropInit[18] = false;
  fElementPropInit[36] = false;
  fElementPropInit[54] = false;
}

//----------------------------------------------------------------------------
NestAlg::NestAlg(double yieldFactor, CLHEP::HepRandomEngine& engine)
  : fYieldFactor(yieldFactor)
  , fExcitationRatio(0.)
  , fNumScintPhotons(0)
  , fNumIonElectrons(0)
  , fEnergyDep(0.)
  , fEngine(engine)
{
  fElementPropInit[2] = false;
  fElementPropInit[10] = false;
  fElementPropInit[18] = false;
  fElementPropInit[36] = false;
  fElementPropInit[54] = false;
}

//----------------------------------------------------------------------------
const G4VParticleChange& NestAlg::CalculateIonizationAndScintillation(G4Track const& aTrack,
                                                                      G4Step  const& aStep)
{
  CLHEP::RandGauss GaussGen(fEngine);
  CLHEP::RandFlat  UniformGen(fEngine);


  // reset the variables accessed by other objects
  // make the energy deposit the energy in this step,
  // set the number of electrons and photons to 0
  fEnergyDep       = aStep.GetTotalEnergyDeposit();
  fNumIonElectrons = 0.;
  fNumScintPhotons = 0.;


  if ( !fYieldFactor ) //set YF=0 when you want S1Light off in your sim
    return fParticleChange;

  bool   fTrackSecondariesFirst = false;
  bool   fExcitedNucleus        = false;
  bool   fVeryHighEnergy        = false;
  bool   fAlpha                 = false;
  bool   fMultipleScattering    = false;
  double fKr83m                 = 0.;

  if( aTrack.GetParentID() == 0 && aTrack.GetCurrentStepNumber() == 1 ) {
    fExcitedNucleus = false; //an initialization or reset
    fVeryHighEnergy = false; //initializes or (later) resets this
    fAlpha = false; //ditto
    fMultipleScattering = false;
  }

  const G4DynamicParticle* aParticle = aTrack.GetDynamicParticle();
  G4ParticleDefinition *pDef = aParticle->GetDefinition();
  G4String particleName = pDef->GetParticleName();
  const G4Material* aMaterial = aStep.GetPreStepPoint()->GetMaterial();
  const G4Material* bMaterial = aStep.GetPostStepPoint()->GetMaterial();

  if((particleName == "neutron" || particleName == "antineutron") &&
     aStep.GetTotalEnergyDeposit() <= 0)
    return fParticleChange;

  // code for determining whether the present/next material is noble
  // element, or, in other words, for checking if either is a valid NEST
  // scintillating material, and save Z for later L calculation, or
  // return if no valid scintillators are found on this step, which is
  // protection against G4Exception or seg. fault/violation
  G4Element *ElementA = NULL, *ElementB = NULL;
  if (aMaterial) {
    const G4ElementVector* theElementVector1 =
      aMaterial->GetElementVector();
    ElementA = (*theElementVector1)[0];
  }
  if (bMaterial) {
    const G4ElementVector* theElementVector2 =
      bMaterial->GetElementVector();
    ElementB = (*theElementVector2)[0];
  }
  G4int z1,z2,j=1; G4bool NobleNow=false,NobleLater=false;
  if (ElementA) z1 = (G4int)(ElementA->GetZ()); else z1 = -1;
  if (ElementB) z2 = (G4int)(ElementB->GetZ()); else z2 = -1;
  if ( z1==2 || z1==10 || z1==18 || z1==36 || z1==54 ) {
    NobleNow = true;
    //    j = (G4int)aMaterial->GetMaterialPropertiesTable()->
    //  GetConstProperty("TOTALNUM_INT_SITES"); //get current number
    //if ( j < 0 ) {
    if ( aTrack.GetParentID() == 0 && !fElementPropInit[z1] ) {
      InitMatPropValues(aMaterial->GetMaterialPropertiesTable(), z1);
      j = 0; //no sites yet
    } //material properties initialized
  } //end of atomic number check
  if ( z2==2 || z2==10 || z2==18 || z2==36 || z2==54 ) {
    NobleLater = true;
    //    j = (G4int)bMaterial->GetMaterialPropertiesTable()->
    //  GetConstProperty("TOTALNUM_INT_SITES");
    //if ( j < 0 ) {
    if ( aTrack.GetParentID() == 0 && !fElementPropInit[z2] ) {
      InitMatPropValues(bMaterial->GetMaterialPropertiesTable(), z2);
      j = 0; //no sites yet
    } //material properties initialized
  } //end of atomic number check

  if ( !NobleNow && !NobleLater )
    return fParticleChange;

  // retrieval of the particle's position, time, attributes at both the
  // beginning and the end of the current step along its track
  G4StepPoint* pPreStepPoint  = aStep.GetPreStepPoint();
  G4StepPoint* pPostStepPoint = aStep.GetPostStepPoint();
  G4ThreeVector x1 = pPostStepPoint->GetPosition();
  G4ThreeVector x0 = pPreStepPoint->GetPosition();
  G4double evtStrt = pPreStepPoint->GetGlobalTime();
  G4double      t0 = pPreStepPoint->GetLocalTime();
  G4double      t1 = pPostStepPoint->GetLocalTime();

  // now check if we're entering a scintillating material (inside) or
  // leaving one (outside), in order to determine (later on in the code,
  // based on the booleans inside & outside) whether to add/subtract
  // energy that can potentially be deposited from the system
  G4bool outside = false, inside = false, InsAndOuts = false;
  G4MaterialPropertiesTable* aMaterialPropertiesTable =
    aMaterial->GetMaterialPropertiesTable();
  if ( NobleNow && !NobleLater ) outside = true;
  if ( !NobleNow && NobleLater ) {
    aMaterial = bMaterial; inside = true; z1 = z2;
    aMaterialPropertiesTable = bMaterial->GetMaterialPropertiesTable();
  }
  if ( NobleNow && NobleLater &&
       aMaterial->GetDensity() != bMaterial->GetDensity() )
    InsAndOuts = true;

  // retrieve scintillation-related material properties
  G4double Density = aMaterial->GetDensity()/(CLHEP::g/CLHEP::cm3);
  G4double nDensity = Density*AVO; //molar mass factor applied below
  G4int Phase = aMaterial->GetState(); //solid, liquid, or gas?
  G4double ElectricField(0.), FieldSign(0.); //for field quenching of S1
  G4bool GlobalFields = false;

  if ( (WIN == 0) && !TOP && !ANE && !SRF && !GAT && !CTH && !BOT && !PMT ) {
    ElectricField = aMaterialPropertiesTable->GetConstProperty("ELECTRICFIELD");
    GlobalFields = true;
  }
  else {
    if ( x1[2] < WIN && x1[2] > TOP && Phase == kStateGas )
      ElectricField = aMaterialPropertiesTable->GetConstProperty("ELECTRICFIELDWINDOW");
    else if ( x1[2] < TOP && x1[2] > ANE && Phase == kStateGas )
      ElectricField = aMaterialPropertiesTable->GetConstProperty("ELECTRICFIELDTOP");
    else if ( x1[2] < ANE && x1[2] > SRF && Phase == kStateGas )
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELDANODE");
    else if ( x1[2] < SRF && x1[2] > GAT && Phase == kStateLiquid )
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELDSURFACE");
    else if ( x1[2] < GAT && x1[2] > CTH && Phase == kStateLiquid )
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELDGATE");
    else if ( x1[2] < CTH && x1[2] > BOT && Phase == kStateLiquid )
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELDCATHODE");
    else if ( x1[2] < BOT && x1[2] > PMT && Phase == kStateLiquid )
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELDBOTTOM");
    else
      ElectricField = aMaterialPropertiesTable->
        GetConstProperty("ELECTRICFIELD");
  }
  if ( ElectricField >= 0 ) FieldSign = 1; else FieldSign = -1;
  ElectricField = std::abs((1e3*ElectricField)/(CLHEP::kilovolt/CLHEP::cm));
  G4double Temperature = aMaterial->GetTemperature();
  G4double ScintillationYield, ResolutionScale, R0 = 1.0*CLHEP::um,
    DokeBirks[3], ThomasImel = 0.00, delta = 1*CLHEP::mm;
  DokeBirks[0] = 0.00; DokeBirks[2] = 1.00;
  G4double PhotMean = 7*CLHEP::eV, PhotWidth = 1.0*CLHEP::eV; //photon properties
  G4double SingTripRatioR, SingTripRatioX, tau1, tau3, tauR = 0*CLHEP::ns;
  switch ( z1 ) { //sort prop. by noble element atomic#
  case 2: //helium
    ScintillationYield = 1 / (41.3*CLHEP::eV); //all W's from noble gas book
    fExcitationRatio = 0.00; //nominal (true value unknown)
    ResolutionScale = 0.2; //Aprile, Bolotnikov, Bolozdynya, Doke
    PhotMean = 15.9*CLHEP::eV;
    tau1 = GaussGen.fire(10.0*CLHEP::ns,0.0*CLHEP::ns);
    tau3 = 1.6e3*CLHEP::ns;
    tauR = GaussGen.fire(13.00*CLHEP::s,2.00*CLHEP::s); //McKinsey et al. 2003
    break;
  case 10: //neon
    ScintillationYield = 1 / (29.2*CLHEP::eV);
    fExcitationRatio = 0.00; //nominal (true value unknown)
    ResolutionScale = 0.13; //Aprile et. al book
    PhotMean = 15.5*CLHEP::eV; PhotWidth = 0.26*CLHEP::eV;
    tau1 = GaussGen.fire(10.0*CLHEP::ns,10.*CLHEP::ns);
    tau3 = GaussGen.fire(15.4e3*CLHEP::ns,200*CLHEP::ns); //Nikkel et al. 2008
    break;
  case 18: //argon
    ScintillationYield = 1 / (19.5*CLHEP::eV);
    fExcitationRatio = 0.21; //Aprile et. al book
    ResolutionScale = 0.107; //Doke 1976
    R0 = 1.568*CLHEP::um; //Mozumder 1995
    if(ElectricField) {
      ThomasImel = 0.156977*pow(ElectricField,-0.1);
      DokeBirks[0] = 0.07*pow((ElectricField/1.0e3),-0.85);
      DokeBirks[2] = 0.00;
    }
    else {
      ThomasImel = 0.099;
      DokeBirks[0] = 0.0003;
      DokeBirks[2] = 0.75;
    } nDensity /= 39.948; //molar mass in grams per mole
    PhotMean = 9.69*CLHEP::eV; PhotWidth = 0.22*CLHEP::eV;
    tau1 = GaussGen.fire(6.5*CLHEP::ns,0.8*CLHEP::ns); //err from wgted avg.
    tau3 = GaussGen.fire(1300*CLHEP::ns,50*CLHEP::ns); //ibid.
    tauR = GaussGen.fire(0.8*CLHEP::ns,0.2*CLHEP::ns); //Kubota 1979
    biExc = 0.6; break;
  case 36: //krypton
    if ( Phase == kStateGas ) ScintillationYield = 1 / (30.0*CLHEP::eV);
    else ScintillationYield = 1 / (15.0*CLHEP::eV);
    fExcitationRatio = 0.08; //Aprile et. al book
    ResolutionScale = 0.05; //Doke 1976
    PhotMean = 8.43*CLHEP::eV;
    tau1 = GaussGen.fire(2.8*CLHEP::ns,.04*CLHEP::ns);
    tau3 = GaussGen.fire(93.*CLHEP::ns,1.1*CLHEP::ns);
    tauR = GaussGen.fire(12.*CLHEP::ns,.76*CLHEP::ns);
    break;
  case 54: //xenon
  default: nDensity /= 131.293;
    ScintillationYield = 48.814+0.80877*Density+2.6721*pow(Density,2.);
    ScintillationYield /= CLHEP::keV; //Units: [#quanta(ph/e-) per keV]
    //W = 13.7 eV for all recoils, Dahl thesis (that's @2.84 g/cm^3)
    //the exciton-to-ion ratio (~0.06 for LXe at 3 g/cm^3)
    fExcitationRatio = 0.4-0.11131*Density-0.0026651*pow(Density,2.);
    ResolutionScale = 1.00 * //Fano factor <<1
      (0.12724-0.032152*Density-0.0013492*pow(Density,2.));
    //~0.1 for GXe w/ formula from Bolotnikov et al. 1995
    if ( Phase == kStateLiquid ) {
      ResolutionScale *= 1.5; //to get it to be ~0.03 for LXe
      R0 = 16.6*CLHEP::um; //for zero electric field
      //length scale above which Doke model used instead of Thomas-Imel
      if(ElectricField) //change it with field (see NEST paper)
        R0 = 69.492*pow(ElectricField,-0.50422)*CLHEP::um;
      if(ElectricField) { //formulae & values all from NEST paper
        DokeBirks[0]= 19.171*pow(ElectricField+25.552,-0.83057)+0.026772;
        DokeBirks[2] = 0.00; //only volume recombination (above)
      }
      else { //zero electric field magnitude
        DokeBirks[0] = 0.18; //volume/columnar recombination factor (A)
        DokeBirks[2] = 0.58; //geminate/Onsager recombination (C)
      }
      //"ThomasImel" is alpha/(a^2*v), the recomb. coeff.
      ThomasImel = 0.05; //aka xi/(4*N_i) from the NEST paper
      //distance used to determine when one is at a new interaction site
      delta = 0.4*CLHEP::mm; //distance ~30 keV x-ray travels in LXe
      PhotMean = 6.97*CLHEP::eV; PhotWidth = 0.23*CLHEP::eV;
      // 178+/-14nmFWHM, taken from Jortner JchPh 42 '65.
      //these singlet and triplet times may not be the ones you're
      //used to, but are the world average: Kubota 79, Hitachi 83 (2
      //data sets), Teymourian 11, Morikawa 89, and Akimov '02
      tau1 = GaussGen.fire(3.1*CLHEP::ns,.7*CLHEP::ns); //err from wgted avg.
      tau3 = GaussGen.fire(24.*CLHEP::ns,1.*CLHEP::ns); //ibid.
    } //end liquid
    else if ( Phase == kStateGas ) {
      if(!fAlpha) fExcitationRatio=0.07; //Nygren NIM A 603 (2009) p. 340
      else { biExc = 1.00;
        ScintillationYield = 1 / (12.98*CLHEP::eV); } //Saito 2003
      R0 = 0.0*CLHEP::um; //all Doke/Birks interactions (except for alphas)
      G4double Townsend = (ElectricField/nDensity)*1e17;
      DokeBirks[0] = 0.0000; //all geminate (except at zero, low fields)
      DokeBirks[2] = 0.1933*pow(Density,2.6199)+0.29754 -
        (0.045439*pow(Density,2.4689)+0.066034)*log10(ElectricField);
      if ( ElectricField>6990 ) DokeBirks[2]=0.0;
      if ( ElectricField<1000 ) DokeBirks[2]=0.2;
      if ( ElectricField<100. ) { DokeBirks[0]=0.18; DokeBirks[2]=0.58; }
      if( Density < 0.061 ) ThomasImel = 0.041973*pow(Density,1.8105);
      else if( Density >= 0.061 && Density <= 0.167 )
        ThomasImel=5.9583e-5+0.0048523*Density-0.023109*pow(Density,2.);
      else ThomasImel = 6.2552e-6*pow(Density,-1.9963);
      if(ElectricField)ThomasImel=1.2733e-5*pow(Townsend/Density,-0.68426);
      // field\density dependence from Kobayashi 2004 and Saito 2003
      PhotMean = 7.1*CLHEP::eV; PhotWidth = 0.2*CLHEP::eV;
      tau1 = GaussGen.fire(5.18*CLHEP::ns,1.55*CLHEP::ns);
      tau3 = GaussGen.fire(100.1*CLHEP::ns,7.9*CLHEP::ns);
    } //end gas information (preliminary guesses)
    else {
      tau1 = 3.5*CLHEP::ns; tau3 = 20.*CLHEP::ns; tauR = 40.*CLHEP::ns;
    } //solid Xe
  }

  // log present and running tally of energy deposition in this section
  G4double anExcitationEnergy = ((const G4Ions*)(pDef))->
    GetExcitationEnergy(); //grab nuclear energy level
  G4double TotalEnergyDeposit = //total energy deposited so far
    aMaterialPropertiesTable->GetConstProperty( "ENERGY_DEPOSIT_TOT" );
  G4bool convert = false, annihil = false;
  //set up special cases for pair production and positron annihilation
  if(pPreStepPoint->GetKineticEnergy()>=(2*CLHEP::electron_mass_c2) &&
     !pPostStepPoint->GetKineticEnergy() &&
     !aStep.GetTotalEnergyDeposit() && aParticle->GetPDGcode()==22) {
    convert = true; TotalEnergyDeposit = CLHEP::electron_mass_c2;
  }
  if(pPreStepPoint->GetKineticEnergy() &&
     !pPostStepPoint->GetKineticEnergy() &&
     aParticle->GetPDGcode()==-11) {
    annihil = true; TotalEnergyDeposit += aStep.GetTotalEnergyDeposit();
  }
  G4bool either = false;
  if(inside || outside || convert || annihil || InsAndOuts) either=true;
  //conditions for returning when energy deposits too low
  if( anExcitationEnergy<100*CLHEP::eV && aStep.GetTotalEnergyDeposit()<1*CLHEP::eV &&
      !either && !fExcitedNucleus )
    return fParticleChange;
  //add current deposit to total energy budget
  if ( !annihil ) TotalEnergyDeposit += aStep.GetTotalEnergyDeposit();
  if ( !convert ) aMaterialPropertiesTable->
                    AddConstProperty( "ENERGY_DEPOSIT_TOT", TotalEnergyDeposit );
  //save current deposit for determining number of quanta produced now
  TotalEnergyDeposit = aStep.GetTotalEnergyDeposit();

  // check what the current "goal" E is for dumping scintillation,
  // often the initial kinetic energy of the parent particle, and deal
  // with all other energy-related matters in this block of code
  G4double InitialKinetEnergy = aMaterialPropertiesTable->
    GetConstProperty( "ENERGY_DEPOSIT_GOL" );
  //if zero, add up initial potential and kinetic energies now
  if ( InitialKinetEnergy == 0 ) {
    G4double tE = pPreStepPoint->GetKineticEnergy()+anExcitationEnergy;
    if ( (fabs(tE-1.8*CLHEP::keV) < CLHEP::eV || fabs(tE-9.4*CLHEP::keV) < CLHEP::eV) &&
         Phase == kStateLiquid && z1 == 54 ) tE = 9.4*CLHEP::keV;
    if ( fKr83m && ElectricField != 0 )
      DokeBirks[2] = 0.10;
    aMaterialPropertiesTable->
      AddConstProperty ( "ENERGY_DEPOSIT_GOL", tE );
    //excited nucleus is special case where accuracy reduced for total
    //energy deposition because of G4 inaccuracies and scintillation is
    //forced-dumped when that nucleus is fully de-excited
    if ( anExcitationEnergy ) fExcitedNucleus = true;
  }
  //if a particle is leaving, remove its kinetic energy from the goal
  //energy, as this will never get deposited (if depositable)
  if(outside){ aMaterialPropertiesTable->
      AddConstProperty("ENERGY_DEPOSIT_GOL",
                       InitialKinetEnergy-pPostStepPoint->GetKineticEnergy());
    if(aMaterialPropertiesTable->
       GetConstProperty("ENERGY_DEPOSIT_GOL")<0)
      aMaterialPropertiesTable->AddConstProperty("ENERGY_DEPOSIT_GOL",0);
  }
  //if a particle is coming back into your scintillator, then add its
  //energy to the goal energy
  if(inside) { aMaterialPropertiesTable->
      AddConstProperty("ENERGY_DEPOSIT_GOL",
                       InitialKinetEnergy+pPreStepPoint->GetKineticEnergy());
    if ( TotalEnergyDeposit > 0 && InitialKinetEnergy == 0 ) {
      aMaterialPropertiesTable->AddConstProperty("ENERGY_DEPOSIT_GOL",0);
      TotalEnergyDeposit = .000000;
    }
  }
  if ( InsAndOuts ) {
    //G4double dribble = pPostStepPoint->GetKineticEnergy() -
    //pPreStepPoint->GetKineticEnergy();
    aMaterialPropertiesTable->
      AddConstProperty("ENERGY_DEPOSIT_GOL",(-0.1*CLHEP::keV)+
                       InitialKinetEnergy-pPostStepPoint->GetKineticEnergy());
    InitialKinetEnergy = bMaterial->GetMaterialPropertiesTable()->
      GetConstProperty("ENERGY_DEPOSIT_GOL");
    bMaterial->GetMaterialPropertiesTable()->
      AddConstProperty("ENERGY_DEPOSIT_GOL",(-0.1*CLHEP::keV)+
                       InitialKinetEnergy+pPreStepPoint->GetKineticEnergy());
    if(aMaterialPropertiesTable->
       GetConstProperty("ENERGY_DEPOSIT_GOL")<0)
      aMaterialPropertiesTable->AddConstProperty("ENERGY_DEPOSIT_GOL",0);
    if ( bMaterial->GetMaterialPropertiesTable()->
         GetConstProperty("ENERGY_DEPOSIT_GOL") < 0 )
      bMaterial->GetMaterialPropertiesTable()->
        AddConstProperty ( "ENERGY_DEPOSIT_GOL", 0 );
  }
  InitialKinetEnergy = aMaterialPropertiesTable->
    GetConstProperty("ENERGY_DEPOSIT_GOL"); //grab current goal E
  if ( annihil ) //if an annihilation occurred, add energy of two gammas
    InitialKinetEnergy += 2*CLHEP::electron_mass_c2;
  //if pair production occurs, then subtract energy to cancel with the
  //energy that will be added in the line above when the e+ dies
  if ( convert )
    InitialKinetEnergy -= 2*CLHEP::electron_mass_c2;
  //update the relevant material property (goal energy)
  aMaterialPropertiesTable->
    AddConstProperty("ENERGY_DEPOSIT_GOL",InitialKinetEnergy);
  if (anExcitationEnergy < 1e-100 && aStep.GetTotalEnergyDeposit()==0 &&
      aMaterialPropertiesTable->GetConstProperty("ENERGY_DEPOSIT_GOL")==0 &&
      aMaterialPropertiesTable->GetConstProperty("ENERGY_DEPOSIT_TOT")==0)
    return fParticleChange;

  G4String procName;
  if ( aTrack.GetCreatorProcess() )
    procName = aTrack.GetCreatorProcess()->GetProcessName();
  else
    procName = "NULL";
  if ( procName == "eBrem" && outside && !OutElectrons )
    fMultipleScattering = true;

  // next 2 codeblocks deal with position-related things
  if ( fAlpha ) delta = 1000.*CLHEP::km;
  G4int i, k, counter = 0; G4double pos[3];
  if ( outside ) { //leaving
    if ( aParticle->GetPDGcode() == 11 && !OutElectrons )
      fMultipleScattering = true;
    x1 = x0; //prevents generation of quanta outside active volume
  } //no scint. for e-'s that leave

  char xCoord[80]; char yCoord[80]; char zCoord[80];
  G4bool exists = false; //for querying whether set-up of new site needed
  for(i=0;i<j;i++) { //loop over all saved interaction sites
    counter = i; //save site# for later use in storing properties
    sprintf(xCoord,"POS_X_%d",i); sprintf(yCoord,"POS_Y_%d",i);
    sprintf(zCoord,"POS_Z_%d",i);
    pos[0] = aMaterialPropertiesTable->GetConstProperty(xCoord);
    pos[1] = aMaterialPropertiesTable->GetConstProperty(yCoord);
    pos[2] = aMaterialPropertiesTable->GetConstProperty(zCoord);
    if ( sqrt(pow(x1[0]-pos[0],2.)+pow(x1[1]-pos[1],2.)+
              pow(x1[2]-pos[2],2.)) < delta ) {
      exists = true; break; //we find interaction is close to an old one
    }
  }
  if(!exists && TotalEnergyDeposit) { //current interaction too far away
    counter = j;
    sprintf(xCoord,"POS_X_%i",j); sprintf(yCoord,"POS_Y_%i",j);
    sprintf(zCoord,"POS_Z_%i",j);
    //save 3-space coordinates of the new interaction site
    aMaterialPropertiesTable->AddConstProperty( xCoord, x1[0] );
    aMaterialPropertiesTable->AddConstProperty( yCoord, x1[1] );
    aMaterialPropertiesTable->AddConstProperty( zCoord, x1[2] );
    j++; //increment number of sites
    aMaterialPropertiesTable-> //save
      AddConstProperty( "TOTALNUM_INT_SITES", j );
  }

  // this is where nuclear recoil "L" factor is handled: total yield is
  // reduced for nuclear recoil as per Lindhard theory

  //we assume you have a mono-elemental scintillator only
  //now, grab A's and Z's of current particle and of material (avg)
  G4double a1 = ElementA->GetA();
  z2 = pDef->GetAtomicNumber();
  G4double a2 = (G4double)(pDef->GetAtomicMass());
  if ( particleName == "alpha" || (z2 == 2 && a2 == 4) )
    fAlpha = true; //used later to get S1 pulse shape correct for alpha
  if ( fAlpha || abs(aParticle->GetPDGcode()) == 2112 )
    a2 = a1; //get average A for element at hand
  G4double epsilon = 11.5*(TotalEnergyDeposit/CLHEP::keV)*pow(z1,(-7./3.));
  G4double gamma = 3.*pow(epsilon,0.15)+0.7*pow(epsilon,0.6)+epsilon;
  G4double kappa = 0.133*pow(z1,(2./3.))*pow(a2,(-1./2.))*(2./3.);
  //check if we are dealing with nuclear recoil (Z same as material)
  if ( (z1 == z2 && pDef->GetParticleType() == "nucleus") ||
       particleName == "neutron" || particleName == "antineutron" ) {
    fYieldFactor=(kappa*gamma)/(1+kappa*gamma); //Lindhard factor
    if ( z1 == 18 && Phase == kStateLiquid )
      fYieldFactor=0.23*(1+exp(-5*epsilon)); //liquid argon L_eff
    //just a few safety checks, like for recombProb below
    if ( fYieldFactor > 1 ) fYieldFactor = 1;
    if ( fYieldFactor < 0 ) fYieldFactor = 0;
    if ( ElectricField == 0 && Phase == kStateLiquid ) {
      if ( z1 == 54 ) ThomasImel = 0.19;
      if ( z1 == 18 ) ThomasImel = 0.25;
    } //special TIB parameters for nuclear recoil only, in LXe and LAr
    fExcitationRatio = 0.69337 +
      0.3065*exp(-0.008806*pow(ElectricField,0.76313));
  }
  else fYieldFactor = 1.000; //default

  // determine ultimate #quanta from current E-deposition (ph+e-)
  G4double MeanNumberOfQuanta = //total mean number of exc/ions
    ScintillationYield*TotalEnergyDeposit;
  //the total number of either quanta produced is equal to product of the
  //work function, the energy deposited, and yield reduction, for NR
  G4double sigma = sqrt(ResolutionScale*MeanNumberOfQuanta); //Fano
  G4int NumQuanta = //stochastic variation in NumQuanta
    G4int(floor(GaussGen.fire(MeanNumberOfQuanta,sigma)+0.5));
  G4double LeffVar = GaussGen.fire(fYieldFactor,0.25*fYieldFactor);
  if (LeffVar > 1) { LeffVar = 1.00000; }
  if (LeffVar < 0) { LeffVar = 0; }
  if ( fYieldFactor < 1 ) NumQuanta = BinomFluct(NumQuanta,LeffVar);
  //if E below work function, can't make any quanta, and if NumQuanta
  //less than zero because Gaussian fluctuated low, update to zero
  if(TotalEnergyDeposit < 1/ScintillationYield || NumQuanta < 0)
    NumQuanta = 0;

  // next section binomially assigns quanta to excitons and ions
  G4int NumExcitons =
    BinomFluct(NumQuanta,fExcitationRatio/(1+fExcitationRatio));
  G4int NumIons = NumQuanta - NumExcitons;

  // this section calculates recombination following the modified Birks'
  // Law of Doke, deposition by deposition, and may be overridden later
  // in code if a low enough energy necessitates switching to the
  // Thomas-Imel box model for recombination instead (determined by site)
  G4double dE, dx=0, LET=0, recombProb;
  dE = TotalEnergyDeposit/CLHEP::MeV;
  if ( particleName != "e-" && particleName != "e+" && z1 != z2 &&
       particleName != "mu-" && particleName != "mu+" ) {
    //in other words, if it's a gamma,ion,proton,alpha,pion,et al. do not
    //use the step length provided by Geant4 because it's not relevant,
    //instead calculate an estimated LET and range of the electrons that
    //would have been produced if Geant4 could track them
    LET = CalculateElectronLET( 1000*dE, z1 );
    if(LET) dx = dE/(Density*LET); //find the range based on the LET
    if(abs(aParticle->GetPDGcode())==2112) dx=0;
  }
  else { //normal case of an e-/+ energy deposition recorded by Geant
    dx = aStep.GetStepLength()/CLHEP::cm;
    if(dx) LET = (dE/dx)*(1/Density); //lin. energy xfer (prop. to dE/dx)
    if ( LET > 0 && dE > 0 && dx > 0 ) {
      G4double ratio = CalculateElectronLET(dE*1e3,z1)/LET;
      if ( j == 1 && ratio < 0.7 && !ThomasImelTail &&
           particleName == "e-" ) {
        dx /= ratio; LET *= ratio; }}
  }
  DokeBirks[1] = DokeBirks[0]/(1-DokeBirks[2]); //B=A/(1-C) (see paper)
  //Doke/Birks' Law as spelled out in the NEST paper
  recombProb = (DokeBirks[0]*LET)/(1+DokeBirks[1]*LET)+DokeBirks[2];
  if ( Phase == kStateLiquid ) {
    if ( z1 == 54 ) recombProb *= (Density/Density_LXe);
    if ( z1 == 18 ) recombProb *= (Density/Density_LAr);
  }
  //check against unphysicality resulting from rounding errors
  if(recombProb<0) recombProb=0;
  if(recombProb>1) recombProb=1;
  //use binomial distribution to assign photons, electrons, where photons
  //are excitons plus recombined ionization electrons, while final
  //collected electrons are the "escape" (non-recombined) electrons
  G4int NumPhotons = NumExcitons + BinomFluct(NumIons,recombProb);
  G4int NumElectrons = NumQuanta - NumPhotons;

  fEnergyDep       = TotalEnergyDeposit;
  fNumIonElectrons = NumElectrons;
  fNumScintPhotons = NumPhotons;

  // next section increments the numbers of excitons, ions, photons, and
  // electrons for the appropriate interaction site; it only appears to
  // be redundant by saving seemingly no longer needed exciton and ion
  // counts, these having been already used to calculate the number of ph
  // and e- above, whereas it does need this later for Thomas-Imel model
  char numExc[80]; char numIon[80]; char numPho[80]; char numEle[80];
  sprintf(numExc,"N_EXC_%i",counter); sprintf(numIon,"N_ION_%i",counter);
  aMaterialPropertiesTable->AddConstProperty( numExc, NumExcitons );
  aMaterialPropertiesTable->AddConstProperty( numIon, NumIons     );
  sprintf(numPho,"N_PHO_%i",counter); sprintf(numEle,"N_ELE_%i",counter);
  aMaterialPropertiesTable->AddConstProperty( numPho, NumPhotons   );
  aMaterialPropertiesTable->AddConstProperty( numEle, NumElectrons );

  // increment and save the total track length, and save interaction
  // times for later, when generating the scintillation quanta
  char trackL[80]; char time00[80]; char time01[80]; char energy[80];
  sprintf(trackL,"TRACK_%i",counter); sprintf(energy,"ENRGY_%i",counter);
  sprintf(time00,"TIME0_%i",counter); sprintf(time01,"TIME1_%i",counter);
  delta = aMaterialPropertiesTable->GetConstProperty( trackL );
  G4double energ = aMaterialPropertiesTable->GetConstProperty( energy );
  delta += dx*CLHEP::cm; energ += dE*CLHEP::MeV;
  aMaterialPropertiesTable->AddConstProperty( trackL, delta );
  aMaterialPropertiesTable->AddConstProperty( energy, energ );
  if ( TotalEnergyDeposit > 0 ) {
    G4double deltaTime = aMaterialPropertiesTable->
      GetConstProperty( time00 );
    //for charged particles, which continuously lose energy, use initial
    //interaction time as the minimum time, otherwise use only the final
    if (aParticle->GetCharge() != 0) {
      if (t0 < deltaTime)
        aMaterialPropertiesTable->AddConstProperty( time00, t0 );
    }
    else {
      if (t1 < deltaTime)
        aMaterialPropertiesTable->AddConstProperty( time00, t1 );
    }
    deltaTime = aMaterialPropertiesTable->GetConstProperty( time01 );
    //find the maximum possible scintillation "birth" time
    if (t1 > deltaTime)
      aMaterialPropertiesTable->AddConstProperty( time01, t1 );
  }

  // begin the process of setting up creation of scint./ionization
  TotalEnergyDeposit=aMaterialPropertiesTable->
    GetConstProperty("ENERGY_DEPOSIT_TOT"); //get the total E deposited
  InitialKinetEnergy=aMaterialPropertiesTable->
    GetConstProperty("ENERGY_DEPOSIT_GOL"); //E that should have been
  if(InitialKinetEnergy > HIENLIM &&
     abs(aParticle->GetPDGcode()) != 2112) fVeryHighEnergy=true;
  G4double safety; //margin of error for TotalE.. - InitialKinetEnergy
  if (fVeryHighEnergy && !fExcitedNucleus) safety = 0.2*CLHEP::keV;
  else safety = 2.*CLHEP::eV;

  //force a scintillation dump for NR and for full nuclear de-excitation
  if( !anExcitationEnergy && pDef->GetParticleType() == "nucleus" &&
      aTrack.GetTrackStatus() != fAlive && !fAlpha )
    InitialKinetEnergy = TotalEnergyDeposit;
  if ( particleName == "neutron" || particleName == "antineutron" )
    InitialKinetEnergy = TotalEnergyDeposit;

  //force a dump of all saved scintillation under the following
  //conditions: energy goal reached, and current particle dead, or an
  //error has occurred and total has exceeded goal (shouldn't happen)
  if( std::abs(TotalEnergyDeposit-InitialKinetEnergy)<safety ||
      TotalEnergyDeposit>=InitialKinetEnergy ){
    dx = 0; dE = 0;
    //calculate the total number of quanta from all sites and all
    //interactions so that the number of secondaries gets set correctly
    NumPhotons = 0; NumElectrons = 0;
    for(i=0;i<j;i++) {
      sprintf(numPho,"N_PHO_%d",i); sprintf(numEle,"N_ELE_%d",i);
      sprintf(trackL,"TRACK_%d",i); sprintf(energy,"ENRGY_%d",i);
      //add up track lengths of all sites, for a total LET calc (later)
      dx += aMaterialPropertiesTable->GetConstProperty(trackL);
      dE += aMaterialPropertiesTable->GetConstProperty(energy);
    }

    G4int buffer = 100; if ( fVeryHighEnergy ) buffer = 1;
    fParticleChange.SetNumberOfSecondaries(buffer*(NumPhotons+NumElectrons));

    if (fTrackSecondariesFirst) {
      if (aTrack.GetTrackStatus() == fAlive )
        fParticleChange.ProposeTrackStatus(fSuspend);
    }


    // begin the loop over all sites which generates all the quanta
    for(i=0;i<j;i++) {
      // get the position X,Y,Z, exciton and ion numbers, total track
      // length of the site, and interaction times
      sprintf(xCoord,"POS_X_%d",i); sprintf(yCoord,"POS_Y_%d",i);
      sprintf(zCoord,"POS_Z_%d",i);
      sprintf(numExc,"N_EXC_%d",i); sprintf(numIon,"N_ION_%d",i);
      sprintf(numPho,"N_PHO_%d",i); sprintf(numEle,"N_ELE_%d",i);
      NumExcitons = (G4int)aMaterialPropertiesTable->
        GetConstProperty( numExc );
      NumIons     = (G4int)aMaterialPropertiesTable->
        GetConstProperty( numIon );
      sprintf(trackL,"TRACK_%d",i); sprintf(energy,"ENRGY_%d",i);
      sprintf(time00,"TIME0_%d",i); sprintf(time01,"TIME1_%d",i);
      delta = aMaterialPropertiesTable->GetConstProperty( trackL );
      energ = aMaterialPropertiesTable->GetConstProperty( energy );
      t0 = aMaterialPropertiesTable->GetConstProperty( time00 );
      t1 = aMaterialPropertiesTable->GetConstProperty( time01 );

      //if site is small enough, override the Doke/Birks' model with
      //Thomas-Imel, but not if we're dealing with super-high energy
      //particles, and if it's NR force Thomas-Imel (though NR should be
      //already short enough in track even up to O(100) keV)
      if ( (delta < R0 && !fVeryHighEnergy) || z2 == z1 || fAlpha ) {
        if( z1 == 54 && ElectricField && //see NEST paper for ER formula
            Phase == kStateLiquid ) {
          if ( abs ( z1 - z2 ) && //electron recoil
               abs ( aParticle->GetPDGcode() ) != 2112 ) {
            ThomasImel = 0.056776*pow(ElectricField,-0.11844);
            if ( fAlpha ) //technically ER, but special
              ThomasImel=0.057675*pow(ElectricField,-0.49362);
          } //end electron recoil (ER)
          else { //nuclear recoil
            // spline of NR data of C.E. Dahl PhD Thesis Princeton '09
            // functions found using zunzun.com
            ThomasImel =
              -0.15169*pow((ElectricField+215.25),0.01811)+0.20952;
          } //end NR information
            // Never let LY exceed 0-field yield!
          if (ThomasImel > 0.19) ThomasImel = 0.19;
          if (ThomasImel < 0.00) ThomasImel = 0.00;
        } //end non-zero E-field segment
        if ( Phase == kStateLiquid ) {
          if ( z1 == 54 ) ThomasImel *= pow((Density/2.84),0.3);
          if ( z1 == 18 ) ThomasImel *= pow((Density/Density_LAr),0.3);
        }
        //calculate the Thomas-Imel recombination probability, which
        //depends on energy via NumIons, but not on dE/dx, and protect
        //against seg fault by ensuring a positive number of ions
        if (NumIons > 0) {
          G4double xi;
          xi = (G4double(NumIons)/4.)*ThomasImel;
          if ( InitialKinetEnergy == 9.4*CLHEP::keV ) {
            G4double NumIonsEff = 1.066e7*pow(t0/CLHEP::ns,-1.303)*
              (0.17163+162.32/(ElectricField+191.39));
            if ( NumIonsEff > 1e6 ) NumIonsEff = 1e6;
            xi = (G4double(NumIonsEff)/4.)*ThomasImel;
          }
          if ( fKr83m && ElectricField==0 )
            xi = (G4double(1.3*NumIons)/4.)*ThomasImel;
          recombProb = 1-log(1+xi)/xi;
          if(recombProb<0) recombProb=0;
          if(recombProb>1) recombProb=1;
        }
        //just like Doke: simple binomial distribution
        NumPhotons = NumExcitons + BinomFluct(NumIons,recombProb);
        NumElectrons = (NumExcitons + NumIons) - NumPhotons;
        //override Doke NumPhotons and NumElectrons
        aMaterialPropertiesTable->
          AddConstProperty( numPho, NumPhotons   );
        aMaterialPropertiesTable->
          AddConstProperty( numEle, NumElectrons );
      }

      // grab NumPhotons/NumElectrons, which come from Birks if
      // the Thomas-Imel block of code above was not executed
      NumPhotons  = (G4int)aMaterialPropertiesTable->
        GetConstProperty( numPho );
      NumElectrons =(G4int)aMaterialPropertiesTable->
        GetConstProperty( numEle );
      // extra Fano factor caused by recomb. fluct.
      G4double FanoFactor =0; //ionization channel
      if(Phase == kStateLiquid && fYieldFactor == 1) {
        FanoFactor =
          2575.9*pow((ElectricField+15.154),-0.64064)-1.4707;
        if ( fKr83m ) TotalEnergyDeposit = 4*CLHEP::keV;
        if ( (dE/CLHEP::keV) <= 100 && ElectricField >= 0 ) {
          G4double keVee = (TotalEnergyDeposit/(100.*CLHEP::keV));
          if ( keVee <= 0.06 )
            FanoFactor *= -0.00075+0.4625*keVee+34.375*pow(keVee,2.);
          else
            FanoFactor *= 0.069554+1.7322*keVee-.80215*pow(keVee,2.);
        }
      }
      if ( Phase == kStateGas && Density>0.5 ) FanoFactor =
                                                 0.42857-4.7857*Density+7.8571*pow(Density,2.);
      if( FanoFactor <= 0 || fVeryHighEnergy ) FanoFactor = 0;
      NumQuanta = NumPhotons + NumElectrons;
      if(z1==54 && FanoFactor) NumElectrons = G4int(
                                                    floor(GaussGen.fire(NumElectrons,
                                                                             sqrt(FanoFactor*NumElectrons))+0.5));
      NumPhotons = NumQuanta - NumElectrons;
      if ( NumElectrons <= 0 ) NumElectrons = 0;
      if (   NumPhotons <= 0 )   NumPhotons = 0;
      else { //other effects
        if ( fAlpha ) //bi-excitonic quenching due to high dE/dx
          NumPhotons = BinomFluct(NumPhotons,biExc);
        NumPhotons = BinomFluct(NumPhotons,QE_EFF);
      } NumElectrons = G4int(floor(NumElectrons*phe_per_e+0.5));




      // new stuff to make Kr-83m work properly
      if(fKr83m || InitialKinetEnergy==9.4*CLHEP::keV) fKr83m += dE/CLHEP::keV;
      if(fKr83m > 41) fKr83m = 0;
      if ( SinglePhase ) //for a 1-phase det. don't propagate e-'s
        NumElectrons = 0; //saves simulation time

      // reset material properties numExc, numIon, numPho, numEle, as
      // their values have been used or stored elsewhere already
      aMaterialPropertiesTable->AddConstProperty( numExc, 0 );
      aMaterialPropertiesTable->AddConstProperty( numIon, 0 );
      aMaterialPropertiesTable->AddConstProperty( numPho, 0 );
      aMaterialPropertiesTable->AddConstProperty( numEle, 0 );

      // start particle creation loop
      if( InitialKinetEnergy < MAX_ENE && InitialKinetEnergy > MIN_ENE &&
          !fMultipleScattering )
        NumQuanta = NumPhotons + NumElectrons;
      else NumQuanta = 0;
      for(k = 0; k < NumQuanta; k++) {
        G4double sampledEnergy;
        std::unique_ptr<G4DynamicParticle> aQuantum;

        // Generate random direction
        G4double cost = 1. - 2.*UniformGen.fire();
        G4double sint = std::sqrt((1.-cost)*(1.+cost));
        G4double phi = CLHEP::twopi*UniformGen.fire();
        G4double sinp = std::sin(phi); G4double cosp = std::cos(phi);
        G4double px = sint*cosp; G4double py = sint*sinp;
        G4double pz = cost;

        // Create momentum direction vector
        G4ParticleMomentum photonMomentum(px, py, pz);

        // case of photon-specific stuff
        if (k < NumPhotons) {
          // Determine polarization of new photon
          G4double sx = cost*cosp;
          G4double sy = cost*sinp;
          G4double sz = -sint;
          G4ThreeVector photonPolarization(sx, sy, sz);
          G4ThreeVector perp = photonMomentum.cross(photonPolarization);
          phi = CLHEP::twopi*UniformGen.fire();
          sinp = std::sin(phi);
          cosp = std::cos(phi);
          photonPolarization = cosp * photonPolarization + sinp * perp;
          photonPolarization = photonPolarization.unit();

          // Generate a new photon or electron:
          sampledEnergy = GaussGen.fire(PhotMean,PhotWidth);
          aQuantum = std::make_unique<G4DynamicParticle>(G4OpticalPhoton::OpticalPhoton(),
                                           photonMomentum);
          aQuantum->SetPolarization(photonPolarization.x(),
                                    photonPolarization.y(),
                                    photonPolarization.z());
        }

        else { // this else statement is for ionization electrons
          if(ElectricField) {
            // point all electrons straight up, for drifting
            G4ParticleMomentum electronMomentum(0, 0, -FieldSign);
            aQuantum = std::make_unique<G4DynamicParticle>(G4ThermalElectron::ThermalElectron(),
                                    electronMomentum);
            if ( Phase == kStateGas ) {
              sampledEnergy = GetGasElectronDriftSpeed(ElectricField,nDensity);
            }
            else
              sampledEnergy = GetLiquidElectronDriftSpeed(Temperature,ElectricField,MillerDriftSpeed,z1);
          }
          else {
            // use "photonMomentum" for the electrons in the case of zero
            // electric field, which is just randomized vector we made
            aQuantum = std::make_unique<G4DynamicParticle>(G4ThermalElectron::ThermalElectron(),
                                    photonMomentum);
            sampledEnergy = 1.38e-23*(CLHEP::joule/CLHEP::kelvin)*Temperature;
          }
        }

        //assign energy to make particle real
        aQuantum->SetKineticEnergy(sampledEnergy);

        // Generate new G4Track object:
        // emission time distribution

        // first an initial birth time is provided that is typically
        // <<1 ns after the initial interaction in the simulation, then
        // singlet, triplet lifetimes, and recombination time, are
        // handled here, to create a realistic S1 pulse shape/timing
        G4double aSecondaryTime = t0+UniformGen.fire()*(t1-t0)+evtStrt;
        if (tau1<0) { tau1=0; }
        if (tau3<0) { tau3=0; }
        if (tauR<0) { tauR=0; }
        if ( aQuantum->GetDefinition()->
             GetParticleName()=="opticalphoton" ) {
          if ( abs(z2-z1) && !fAlpha && //electron recoil
               abs(aParticle->GetPDGcode()) != 2112 ) {
            LET = (energ/CLHEP::MeV)/(delta/CLHEP::cm)*(1/Density); //avg LET over all
            //in future, this will be done interaction by interaction
            // Next, find the recombination time, which is LET-dependent
            // via ionization density (Kubota et al. Phys. Rev. B 20
            // (1979) 3486). We find the LET-dependence by fitting to the
            // E-dependence (Akimov et al. Phys. Lett. B 524 (2002) 245).
            if ( Phase == kStateLiquid && z1 == 54 )
              tauR = 3.5*((1+0.41*LET)/(0.18*LET))*CLHEP::ns
                *exp(-0.00900*ElectricField);
            //field dependence based on fitting Fig. 9 of Dawson et al.
            //NIM A 545 (2005) 690
            //singlet-triplet ratios adapted from Kubota 1979, converted
            //into correct units to work here, and separately done for
            //excitation and recombination processes for electron recoils
            //and assumed same for all LET (may vary)
            SingTripRatioX = GaussGen.fire(0.17,0.05);
            SingTripRatioR = GaussGen.fire(0.8,0.2);
            if ( z1 == 18 ) {
              SingTripRatioR = 0.2701+0.003379*LET-4.7338e-5*pow(LET,2.)
                +8.1449e-6*pow(LET,3.); SingTripRatioX = SingTripRatioR;
              if( LET < 3 ) {
                SingTripRatioX = GaussGen.fire(0.36,0.06);
                SingTripRatioR = GaussGen.fire(0.5,0.2); }
            }
          }
          else if ( fAlpha ) { //alpha particles
            SingTripRatioR = GaussGen.fire(2.3,0.51);
            //currently based on Dawson 05 and Tey. 11 (arXiv:1103.3689)
            //real ratio is likely a gentle function of LET
            if (z1==18) SingTripRatioR = (-0.065492+1.9996
                                          *exp(-dE/CLHEP::MeV))/(1+0.082154/pow(dE/CLHEP::MeV,2.)) + 2.1811;
            SingTripRatioX = SingTripRatioR;
          }
          else { //nuclear recoil
            //based loosely on Hitachi et al. Phys. Rev. B 27 (1983) 5279
            //with an eye to reproducing Akimov 2002 Fig. 9
            SingTripRatioR = GaussGen.fire(7.8,1.5);
            if (z1==18) SingTripRatioR = 0.22218*pow(energ/CLHEP::keV,0.48211);
            SingTripRatioX = SingTripRatioR;
          }
          // now, use binomial distributions to determine singlet and
          // triplet states (and do separately for initially excited guys
          // and recombining)
          if ( k > NumExcitons ) {
            //the recombination time is non-exponential, but approximates
            //to exp at long timescales (see Kubota '79)
            aSecondaryTime += tauR*(1./UniformGen.fire()-1);
            if(UniformGen.fire()<SingTripRatioR/(1+SingTripRatioR))
              aSecondaryTime -= tau1*log(UniformGen.fire());
            else aSecondaryTime -= tau3*log(UniformGen.fire());
          }
          else {
            if(UniformGen.fire()<SingTripRatioX/(1+SingTripRatioX))
              aSecondaryTime -= tau1*log(UniformGen.fire());
            else aSecondaryTime -= tau3*log(UniformGen.fire());
          }
        }
        else { //electron trapping at the liquid/gas interface
          G4double gainField = 12;
          G4double tauTrap = 884.83-62.069*gainField;
          if ( Phase == kStateLiquid )
            aSecondaryTime -= tauTrap*CLHEP::ns*log(UniformGen.fire());
        }

        // emission position distribution --
        // Generate the position of a new photon or electron, with NO
        // stochastic variation because that could lead to particles
        // being mistakenly generated outside of your active region by
        // Geant4, but real-life finite detector position resolution
        // wipes out any effects from here anyway...
        std::string sx(xCoord);
        std::string sy(yCoord);
        std::string sz(zCoord);
        x0[0] = aMaterialPropertiesTable->GetConstProperty( xCoord );
        x0[1] = aMaterialPropertiesTable->GetConstProperty( yCoord );
        x0[2] = aMaterialPropertiesTable->GetConstProperty( zCoord );
        G4double radius = sqrt(pow(x0[0],2.)+pow(x0[1],2.));
        //re-scale radius to ensure no generation of quanta outside
        //the active volume of your simulation due to Geant4 rounding
        if ( radius >= R_TOL ) {
          if (x0[0] == 0) { x0[0] = 1*CLHEP::nm; }
          if (x0[1] == 0) { x0[1] = 1*CLHEP::nm; }
          radius -= R_TOL; phi = atan ( x0[1] / x0[0] );
          x0[0] = fabs(radius*cos(phi))*((fabs(x0[0]))/(x0[0]));
          x0[1] = fabs(radius*sin(phi))*((fabs(x0[1]))/(x0[1]));
        }
        //position of the new secondary particle is ready for use
        G4ThreeVector aSecondaryPosition = x0;
        if ( k >= NumPhotons && diffusion && ElectricField > 0 ) {
          G4double D_T = 64*pow(1e-3*ElectricField,-.17);
          //fit to Aprile and Doke 2009, arXiv:0910.4956 (Fig. 12)
          G4double D_L = 13.859*pow(1e-3*ElectricField,-0.58559);
          //fit to Aprile and Doke and Sorensen 2011, arXiv:1102.2865
          if ( Phase == kStateLiquid && z1 == 18 ) {
            D_T = 93.342*pow(ElectricField/nDensity,0.041322);
            D_L = 0.15 * D_T; }
          if ( Phase == kStateGas && z1 == 54 ) {
            D_L=4.265+19097/ElectricField-1.7397e6/pow(ElectricField,2.)+
              1.2477e8/pow(ElectricField,3.); D_T *= 0.01;
          } D_T *= CLHEP::cm2/CLHEP::s; D_L *= CLHEP::cm2/CLHEP::s;
          if (ElectricField<100 && Phase == kStateLiquid) D_L = 8*CLHEP::cm2/CLHEP::s;
          G4double vDrift = sqrt((2*sampledEnergy)/(EMASS));
          if ( BORDER == 0 ) x0[2] = 0;
          G4double sigmaDT = sqrt(2*D_T*fabs(BORDER-x0[2])/vDrift);
          G4double sigmaDL = sqrt(2*D_L*fabs(BORDER-x0[2])/vDrift);
          G4double dr = std::abs(GaussGen.fire(0.,sigmaDT));
          phi = CLHEP::twopi * UniformGen.fire();
          aSecondaryPosition[0] += cos(phi) * dr;
          aSecondaryPosition[1] += sin(phi) * dr;
          aSecondaryPosition[2] += GaussGen.fire(0.,sigmaDL);
          radius = std::sqrt(std::pow(aSecondaryPosition[0],2.)+
                             std::pow(aSecondaryPosition[1],2.));
          if(aSecondaryPosition[2] >= BORDER && Phase == kStateLiquid) {
            if ( BORDER != 0 ) aSecondaryPosition[2] = BORDER - R_TOL; }
          if(aSecondaryPosition[2] <= PMT && !GlobalFields)
            aSecondaryPosition[2] = PMT + R_TOL;
        } //end of electron diffusion code

          // GEANT4 business: stuff you need to make a new track
        if ( aSecondaryTime < 0 ) aSecondaryTime = 0; //no neg. time
        /*
          auto aSecondaryTrack =
          std::make_unique<G4Track>(aQuantum,aSecondaryTime,aSecondaryPosition);
          if ( k < NumPhotons || radius < R_MAX )
          {

        */
      }

      //reset bunch of things when done with an interaction site
      aMaterialPropertiesTable->AddConstProperty( xCoord, 999*CLHEP::km );
      aMaterialPropertiesTable->AddConstProperty( yCoord, 999*CLHEP::km );
      aMaterialPropertiesTable->AddConstProperty( zCoord, 999*CLHEP::km );
      aMaterialPropertiesTable->AddConstProperty( trackL, 0*CLHEP::um );
      aMaterialPropertiesTable->AddConstProperty( energy, 0*CLHEP::eV );
      aMaterialPropertiesTable->AddConstProperty( time00, DBL_MAX );
      aMaterialPropertiesTable->AddConstProperty( time01, -1*CLHEP::ns );

    } //end of interaction site loop

      //more things to reset...
    aMaterialPropertiesTable->
      AddConstProperty( "TOTALNUM_INT_SITES", 0 );
    aMaterialPropertiesTable->
      AddConstProperty( "ENERGY_DEPOSIT_TOT", 0*CLHEP::keV );
    aMaterialPropertiesTable->
      AddConstProperty( "ENERGY_DEPOSIT_GOL", 0*CLHEP::MeV );
    fExcitedNucleus = false;
    fAlpha = false;
  }

  //don't do anything when you're not ready to scintillate
  else {
    fParticleChange.SetNumberOfSecondaries(0);
    return fParticleChange;
  }

  return fParticleChange;
}

//----------------------------------------------------------------------------
G4double NestAlg::GetGasElectronDriftSpeed(G4double /*efieldinput*/,
                                           G4double /*density*/)
{
  std::cout << "WARNING: NestAlg::GetGasElectronDriftSpeed(G4double, G4double) "
            << "is not defined, returning bogus value of -999." << std::endl;

  return -999.;
}


//----------------------------------------------------------------------------
G4double NestAlg::GetLiquidElectronDriftSpeed(G4double tempinput,
                                              G4double efieldinput,
                                              G4bool Miller,
                                              G4int Z) {
  if(efieldinput<0) efieldinput *= (-1);
  //Liquid equation one (165K) coefficients
  G4double onea=144623.235704015,
    oneb=850.812714257629,
    onec=1192.87056676815,
    oned=-395969.575204061,
    onef=-355.484170008875,
    oneg=-227.266219627672,
    oneh=223831.601257495,
    onei=6.1778950907965,
    onej=18.7831533426398,
    onek=-76132.6018884368;
  //Liquid equation two (200K) coefficients
  G4double twoa=17486639.7118995,
    twob=-113.174284723134,
    twoc=28.005913193763,
    twod=167994210.094027,
    twof=-6766.42962575088,
    twog=901.474643115395,
    twoh=-185240292.471665,
    twoi=-633.297790813084,
    twoj=87.1756135457949;
  //Liquid equation three (230K) coefficients
  G4double thra=10626463726.9833,
    thrb=224025158.134792,
    thrc=123254826.300172,
    thrd=-4563.5678061122,
    thrf=-1715.269592063,
    thrg=-694181.921834368,
    thrh=-50.9753281079838,
    thri=58.3785811395493,
    thrj=201512.080026704;
  G4double y1=0,y2=0,f1=0,f2=0,f3=0,edrift=0,
    t1=0,t2=0,slope=0,intercept=0;

  //Equations defined
  f1=onea/(1+exp(-(efieldinput-oneb)/onec))+oned/
    (1+exp(-(efieldinput-onef)/oneg))+
    oneh/(1+exp(-(efieldinput-onei)/onej))+onek;
  f2=twoa/(1+exp(-(efieldinput-twob)/twoc))+twod/
    (1+exp(-(efieldinput-twof)/twog))+
    twoh/(1+exp(-(efieldinput-twoi)/twoj));
  f3=thra*exp(-thrb*efieldinput)+thrc*exp(-(pow(efieldinput-thrd,2))/
                                          (thrf*thrf))+
    thrg*exp(-(pow(efieldinput-thrh,2)/(thri*thri)))+thrj;

  if(efieldinput<20 && efieldinput>=0) {
    f1=2951*efieldinput;
    f2=5312*efieldinput;
    f3=7101*efieldinput;
  }
  //Cases for tempinput decides which 2 equations to use lin. interpolation
  if(tempinput<200.0 && tempinput>165.0) {
    y1=f1;
    y2=f2;
    t1=165.0;
    t2=200.0;
  }
  if(tempinput<230.0 && tempinput>200.0) {
    y1=f2;
    y2=f3;
    t1=200.0;
    t2=230.0;
  }
  if((tempinput>230.0 || tempinput<165.0) && !Miller) {
    G4cout << "\nWARNING: TEMPERATURE OUT OF RANGE (165-230 K)\n";
    return 0;
  }
  if (tempinput == 165.0) edrift = f1;
  else if (tempinput == 200.0) edrift = f2;
  else if (tempinput == 230.0) edrift = f3;
  else { //Linear interpolation
    //frac=(tempinput-t1)/(t2-t1);
    slope = (y1-y2)/(t1-t2);
    intercept=y1-slope*t1;
    edrift=slope*tempinput+intercept;
  }

  if ( Miller ) {
    if ( efieldinput <= 40. )
      edrift = -0.13274+0.041082*efieldinput-0.0006886*pow(efieldinput,2.)+
        5.5503e-6*pow(efieldinput,3.);
    else
      edrift = 0.060774*efieldinput/pow(1+0.11336*pow(efieldinput,0.5218),2.);
    if ( efieldinput >= 1e5 ) edrift = 2.7;
    if ( efieldinput >= 100 )
      edrift -= 0.017 * ( tempinput - 163 );
    else
      edrift += 0.017 * ( tempinput - 163 );
    edrift *= 1e5; //put into units of cm/sec. from mm/usec.
  }
  if ( Z == 18 ) edrift = 1e5 * (.097384*pow(log10(efieldinput),3.0622)-.018614*sqrt(efieldinput) );
  if ( edrift < 0 ) edrift = 0.;
  edrift = 0.5*EMASS*pow(edrift*CLHEP::cm/CLHEP::s,2.);
  return edrift;
}

//----------------------------------------------------------------------------
G4double NestAlg::CalculateElectronLET ( G4double E, G4int Z ) {
  G4double LET;
  switch ( Z ) {
  case 54:
    //use a spline fit to online ESTAR data
    if ( E >= 1 ) LET = 58.482-61.183*log10(E)+19.749*pow(log10(E),2)+
                    2.3101*pow(log10(E),3)-3.3469*pow(log10(E),4)+
                    0.96788*pow(log10(E),5)-0.12619*pow(log10(E),6)+0.0065108*pow(log10(E),7);
    //at energies <1 keV, use a different spline, determined manually by
    //generating sub-keV electrons in Geant4 and looking at their ranges, since
    //ESTAR does not go this low
    else if ( E>0 && E<1 ) LET = 6.9463+815.98*E-4828*pow(E,2)+17079*pow(E,3)-
                             36394*pow(E,4)+44553*pow(E,5)-28659*pow(E,6)+7483.8*pow(E,7);
    else
      LET = 0;
    break;
  case 18: default:
    if ( E >= 1 ) LET = 116.70-162.97*log10(E)+99.361*pow(log10(E),2)-
                    33.405*pow(log10(E),3)+6.5069*pow(log10(E),4)-
                    0.69334*pow(log10(E),5)+.031563*pow(log10(E),6);
    else if ( E>0 && E<1 ) LET = 100;
    else
      LET = 0;
  }
  return LET;
}

//----------------------------------------------------------------------------
G4int NestAlg::BinomFluct ( G4int N0, G4double prob ) {
  CLHEP::RandGauss GaussGen(fEngine);
  CLHEP::RandFlat  UniformGen(fEngine);

  G4double mean = N0*prob;
  G4double sigma = sqrt(N0*prob*(1-prob));
  G4int N1 = 0;
  if ( prob == 0.00 ) return N1;
  if ( prob == 1.00 ) return N0;

  if ( N0 < 10 ) {
    for(G4int i = 0; i < N0; i++) {
      if(UniformGen.fire() < prob) N1++;
    }
  }
  else {
    N1 = G4int(floor(GaussGen.fire(mean,sigma)+0.5));
  }
  if ( N1 > N0 ) N1 = N0;
  if ( N1 < 0 ) N1 = 0;
  return N1;
}

//----------------------------------------------------------------------------
void NestAlg::InitMatPropValues ( G4MaterialPropertiesTable *nobleElementMat,
                                  int z) {
  char xCoord[80]; char yCoord[80]; char zCoord[80];
  char numExc[80]; char numIon[80]; char numPho[80]; char numEle[80];
  char trackL[80]; char time00[80]; char time01[80]; char energy[80];

  // for loop to initialize the interaction site mat'l properties
  for( G4int i=0; i<10000; i++ ) {
    sprintf(xCoord,"POS_X_%d",i); sprintf(yCoord,"POS_Y_%d",i);
    sprintf(zCoord,"POS_Z_%d",i);
    nobleElementMat->AddConstProperty( xCoord, 999*CLHEP::km );
    nobleElementMat->AddConstProperty( yCoord, 999*CLHEP::km );
    nobleElementMat->AddConstProperty( zCoord, 999*CLHEP::km );
    sprintf(numExc,"N_EXC_%d",i); sprintf(numIon,"N_ION_%d",i);
    sprintf(numPho,"N_PHO_%d",i); sprintf(numEle,"N_ELE_%d",i);
    nobleElementMat->AddConstProperty( numExc, 0 );
    nobleElementMat->AddConstProperty( numIon, 0 );
    nobleElementMat->AddConstProperty( numPho, 0 );
    nobleElementMat->AddConstProperty( numEle, 0 );
    sprintf(trackL,"TRACK_%d",i); sprintf(energy,"ENRGY_%d",i);
    sprintf(time00,"TIME0_%d",i); sprintf(time01,"TIME1_%d",i);
    nobleElementMat->AddConstProperty( trackL, 0*CLHEP::um );
    nobleElementMat->AddConstProperty( energy, 0*CLHEP::eV );
    nobleElementMat->AddConstProperty( time00, DBL_MAX );
    nobleElementMat->AddConstProperty( time01,-1*CLHEP::ns );
  }

  // we initialize the total number of interaction sites, a variable for
  // updating the amount of energy deposited thus far in the medium, and a
  // variable for storing the amount of energy expected to be deposited
  nobleElementMat->AddConstProperty( "TOTALNUM_INT_SITES", 0 );
  nobleElementMat->AddConstProperty( "ENERGY_DEPOSIT_TOT", 0*CLHEP::keV );
  nobleElementMat->AddConstProperty( "ENERGY_DEPOSIT_GOL", 0*CLHEP::MeV );

  fElementPropInit[z] = true;

  return;
}

//----------------------------------------------------------------------------
G4double UnivScreenFunc ( G4double E, G4double Z, G4double A ) {
  G4double a_0 = 5.29e-11*CLHEP::m; G4double a = 0.626*a_0*pow(Z,(-1./3.));
  G4double epsilon_0 = 8.854e-12*(CLHEP::farad/CLHEP::m);
  G4double epsilon = (a*E*2.*CLHEP::twopi*epsilon_0)/(2*pow(CLHEP::eplus,2.)*pow(Z,2.));
  G4double zeta_0 = pow(Z,(1./6.)); G4double m_N = A*1.66e-27*CLHEP::kg;
  G4double hbar = 6.582e-16*CLHEP::eV*CLHEP::s;
  if ( Z == 54 ) {
    epsilon *= 1.068; //zeta_0 = 1.63;
  } //special case for LXe from Bezrukov et al. 2011
  G4double s_n = log(1+1.1383*epsilon)/(2.*(epsilon +
                                            0.01321*pow(epsilon,0.21226) +
                                            0.19593*sqrt(epsilon)));
  G4double s_e = (a_0*zeta_0/a)*hbar*sqrt(8*epsilon*2.*CLHEP::twopi*epsilon_0/
                                          (a*m_N*pow(CLHEP::eplus,2.)));
  return 1.38e5*0.5*(1+tanh(50*epsilon-0.25))*epsilon*(s_e/s_n);
}