--- /dev/null
+///////////////////////////////////////////////////////////////////////////
+//
+// Copyright 2010
+//
+// This file is part of starlight.
+//
+// starlight is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// starlight is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with starlight. If not, see <http://www.gnu.org/licenses/>.
+//
+///////////////////////////////////////////////////////////////////////////
+//
+// File and Version Information:
+// $Rev:: 164 $: revision of last commit
+// $Author:: odjuvsla $: author of last commit
+// $Date:: 2013-10-06 16:18:08 +0200 #$: date of last commit
+//
+// Description:
+//
+//
+//
+///////////////////////////////////////////////////////////////////////////
+
+
+#include <iostream>
+#include <fstream>
+#include <cmath>
+
+#include "starlightconstants.h"
+#include "inputParameters.h"
+#include "reportingUtils.h"
+#include "bessel.h"
+#include "beam.h"
+
+
+using namespace std;
+using namespace starlightConstants;
+
+//______________________________________________________________________________
+beam::beam(const int Z,
+ const int A,
+ const double bdeuteron,
+ const bool dAuCoherentProduction)
+ : nucleus(Z,
+ A,
+ bdeuteron,
+ dAuCoherentProduction)
+ ,_beamLorentzGamma(inputParametersInstance.beamLorentzGamma())
+{
+}
+
+
+//______________________________________________________________________________
+beam::~beam()
+{ }
+
+
+//______________________________________________________________________________
+double beam::photonFlux(const double impactparameter,
+ const double photonEnergy) const
+{
+ // function for the calculation of the "photon density".
+ // photonFlux = number of photons / (energy * area)
+ // assume beta = 1 and gamma >> 1, i.e. neglect the (1 / gamma^2) * K_0(x) term
+
+ const double X
+ = (impactparameter * photonEnergy) / (_beamLorentzGamma * hbarc);
+ if (X <= 0)
+ printWarn << "X = " << X << endl;
+
+ const double factor1 = (double(Z() * Z()) * alpha) / (pi * pi);
+ const double factor2 = 1. / (photonEnergy * impactparameter * impactparameter);
+ const double bessel = bessel::dbesk1(X);
+ const double factor3 = X * X * bessel * bessel;
+
+ return factor1 * factor2 * factor3;
+}