MuMinusCaptureFix Class Reference

List of all members.

---

Detailed Description

class MuMinusCaptureFix will fixup the G4MuonMinusCaptureAtRest process.

The constructor replaces muMinusCaptureAtRest with this class, so all that is needed is to create an instance of this class with the desired arguments. That must occur AFTER the physics processes are completely set up but before any tracking.

This class adds additional neutrons to mu- capture. The neutrons are added with a Poisson distribution with mean=neutronMeanNumber, and have an exponential distribution in kinetic energy: (1/neutronMeanEnergy)*exp(-KE/neutronMeanEnergy) As the muonic atom cascades to its ground state it forgets the incident mu- direction, so neutrons are generated isotropically in the lab.

The extra neutrons are added only to those captures that are hadronic (i.e. not decay in orbit). The value of neutronMeanNumber should reflect this. The default values correspond to Al.

Author: Tom Roberts Date: September 8, 2010 This class is completely independent of G4beamline and can be copied into other code (keep the above include-s and definitions).

Public Member Functions
	MuMinusCaptureFix (double _neutronMeanNumber=DEFAULT_NEUTRONMEANNUMBER, double _neutronMeanEnergy=DEFAULT_NEUTRONMEANENERGY)
	Constructor.
virtual G4VParticleChange *	AtRestDoIt (const G4Track &, const G4Step &)
	AtRestDoit() from G4MuonMinusCaptureAtRest.
G4Track *	createExtraNeutron (const G4ThreeVector &position, double time)
	createExtraNeutron() creates an extra neutron with the given KE distribution, isotropically at position.
Private Attributes
double	neutronMeanNumber
double	neutronMeanEnergy
G4ParticleChange	change

---

Constructor & Destructor Documentation

MuMinusCaptureFix::MuMinusCaptureFix	(	double	_neutronMeanNumber = DEFAULT_NEUTRONMEANNUMBER,
		double	_neutronMeanEnergy = DEFAULT_NEUTRONMEANENERGY
	)

Constructor.

References neutronMeanEnergy, and neutronMeanNumber.

                        : G4MuonMinusCaptureAtRest("muMinusCaptureAtRestFIX"),
                          change()
{
        neutronMeanNumber = _neutronMeanNumber;
        neutronMeanEnergy = _neutronMeanEnergy;

        // replace G4MuonMinusCaptureAtRest with this MuMinusCaptureFix.
        G4ParticleDefinition *mu = G4MuonMinus::MuonMinus();
        G4ProcessManager *pm = mu->GetProcessManager();
again:  G4ProcessVector *pv = pm->GetProcessList();
        int n = pv->size();
        for(int i=0; i<n; ++i) {
                G4VProcess *process = (*pv)[i];
                if(process->GetProcessName() == "muMinusCaptureAtRest") {
                        pm->RemoveProcess(process);
                        goto again;
                }
        }
        pm->AddProcess(this,ordDefault,-1,-1);
}

---

Member Function Documentation

G4VParticleChange * MuMinusCaptureFix::AtRestDoIt	(	const G4Track &	track,
		const G4Step &	step
	)			[virtual]

AtRestDoit() from G4MuonMinusCaptureAtRest.

References change, createExtraNeutron(), and neutronMeanNumber.

{
        int nExtraNeutrons = CLHEP::RandPoissonQ::shoot(neutronMeanNumber);

        // localtime will become the earliest time of any secondary hadron
        // from the original process; extra neutrons are not added to
        // decay in orbit captures (events with no secondary hadrons).
        // Note the capture gives prompt gammas which must not be considered.
        double localtime=DBL_MAX;
        bool haveHadron=false;

        // call original process's AtRestDoit()
        G4VParticleChange *p=G4MuonMinusCaptureAtRest::AtRestDoIt(track,step);
        int n0=p->GetNumberOfSecondaries();
        G4ThreeVector position=track.GetPosition();

        // setup a ParticleChange with room for the extra neutrons (this is a
        // copy of all modifications to aParticleChange in the original code)
        change.Initialize(track);
        change.SetNumberOfSecondaries(n0+nExtraNeutrons);
        for(int i=0; i<n0; ++i) {
                G4Track *t=p->GetSecondary(i);
                change.AddSecondary(new G4Track(*t)); // avoid double deletes
                G4String type=t->GetDefinition()->GetParticleType();
                if(type == "baryon" || type == "meson" || type == "nucleus") {
                        haveHadron = true;
                        double time=t->GetGlobalTime();
                        if(time < localtime) localtime = time;
                }
        }
        change.ProposeLocalEnergyDeposit(0.0);
        change.ProposeTrackStatus(fStopAndKill);
        p->Clear();

        // store extra neutrons
        if(haveHadron) {
            for(int i=0; i<nExtraNeutrons; ++i) {
                G4Track *neutron = createExtraNeutron(position,localtime);
                change.AddSecondary(neutron);
            }
        }

        return &change;
}

G4Track * MuMinusCaptureFix::createExtraNeutron	(	const G4ThreeVector &	position,
		double	time
	)

createExtraNeutron() creates an extra neutron with the given KE distribution, isotropically at position.

References KE, M_PI, and neutronMeanEnergy.

Referenced by AtRestDoIt().

{
        G4ParticleDefinition *neutron=G4Neutron::Neutron();
        double KE=CLHEP::RandExponential::shoot(neutronMeanEnergy);
        double costheta=2.0*(G4UniformRand()-0.5);
        double sintheta=sqrt(1.0-costheta*costheta);
        double phi=2.0*M_PI*G4UniformRand();
        G4ThreeVector direction(sintheta*cos(phi),sintheta*sin(phi),costheta);
        G4DynamicParticle *dyn = new G4DynamicParticle(neutron,direction,KE);
        G4Track *track = new G4Track(dyn,time,position);
        return track;
}

---

Member Data Documentation

double MuMinusCaptureFix::neutronMeanNumber [private]

Referenced by AtRestDoIt(), and MuMinusCaptureFix().

double MuMinusCaptureFix::neutronMeanEnergy [private]

Referenced by createExtraNeutron(), and MuMinusCaptureFix().

G4ParticleChange MuMinusCaptureFix::change [private]

Referenced by AtRestDoIt().

---

The documentation for this class was generated from the following file:

• BLCMDmuminuscapturefix.cc