Resolve "Reviewing physics behind particle matter interaction models"

• Closes #634 (closed)
• Cleans up, coding style fixes and update license header to touched files

src/Classic/Solvers/CollimatorPhysics.cpp

 //
 // Class CollimatorPhysics
-//
-// Defines the collimator physics models
+//   Defines the collimator physics models
 //
 // Copyright (c) 2009 - 2020, Bi, Yang, Stachel, Adelmann
 //                            Paul Scherrer Institut, Villigen PSI, Switzerland
@@ -17,7 +16,6 @@
 // You should have received a copy of the GNU General Public License
 // along with OPAL.  If not, see <https://www.gnu.org/licenses/>.
 //
-
 #include "Solvers/CollimatorPhysics.hh"
 #include "Physics/Physics.h"
 #include "Physics/Material.h"
@@ -39,10 +37,10 @@
 
 #include <gsl/gsl_randist.h>
 
+#include <algorithm>
 #include <cmath>
-#include <iostream>
 #include <fstream>
-#include <algorithm>
+#include <iostream>
 
 #include <sys/time.h>
 
@@ -152,8 +150,8 @@ CollimatorPhysics::CollimatorPhysics(const std::string& name,
 
     lossDs_m = std::unique_ptr<LossDataSink>(new LossDataSink(getName(), !Options::asciidump));
 
-    DegraderApplyTimer_m = IpplTimings::getTimer("DegraderApply");
-    DegraderLoopTimer_m = IpplTimings::getTimer("DegraderLoop");
+    DegraderApplyTimer_m   = IpplTimings::getTimer("DegraderApply");
+    DegraderLoopTimer_m    = IpplTimings::getTimer("DegraderLoop");
     DegraderDestroyTimer_m = IpplTimings::getTimer("DegraderDestroy");
 }
 
@@ -283,15 +281,14 @@ void CollimatorPhysics::computeInteraction() {
         }
     }
 
-    /*
-      delete absorbed particles
-    */
+    // delete absorbed particles
     deleteParticleFromLocalVector();
 }
 
-/// Energy Loss:  using the Bethe-Bloch equation.
-/// Energy straggling: For relatively thick absorbers such that the number of collisions is large,
-/// the energy loss distribution is shown to be Gaussian in form.
+/// Energy Loss: using the Bethe-Bloch equation.
+/// In low-energy region use Anderson-Ziegler fitting (only for protons)
+/// Energy straggling: For relatively thick absorbers such that the number of collisions
+/// is large, the energy loss distribution is shown to be Gaussian in form.
 /// See Particle Physics Booklet, chapter 'Passage of particles through matter' or
 /// Review of Particle Physics, DOI: 10.1103/PhysRevD.86.010001, page 329 ff
 // -------------------------------------------------------------------------
@@ -345,7 +342,6 @@ bool CollimatorPhysics::computeEnergyLoss(Vector_t& P,
         Ekin += deltasrho * dEdx;
     }
 
-
     if (includeFluctuations) {
         double sigma_E = std::sqrt(K * massElectron_keV * rho_m * (Z_m / A_m) * deltas * m2cm);
         Ekin += gsl_ran_gaussian(rGen_m, sigma_E);
@@ -361,9 +357,9 @@ bool CollimatorPhysics::computeEnergyLoss(Vector_t& P,
 
 
 // Implement the rotation in 2 dimensions here
-// For details see:
-//  J. Beringer et al. (Particle Data Group), "Passage of particles through matter"
-//  Phys. Rev. D 86, 010001 (2012),
+// For details see: J. Beringer et al. (Particle Data Group),
+// "Passage of particles through matter", Phys. Rev. D 86, 010001 (2012)
+// -------------------------------------------------------------------------
 void  CollimatorPhysics::applyRotation(Vector_t& P,
                                        Vector_t& R,
                                        double shift,
@@ -488,9 +484,7 @@ void CollimatorPhysics::addBackToBunch(PartBunchBase<double, 3>* bunch) {
         }
     }
 
-    /*
-      delete particles that went to the bunch
-    */
+    // delete particles that went to the bunch
     deleteParticleFromLocalVector();
 }
 
@@ -596,8 +590,8 @@ namespace {
 
 void CollimatorPhysics::deleteParticleFromLocalVector() {
     /*
-      the particle to be deleted (label < 0) are all at the end of
-      the vector.
+      the particle to be deleted (label < 0) are all 
+      at the end of the vector.
     */
     sort(locParts_m.begin(), locParts_m.end(), myCompF);