Editing Geant4 Cosmic Ray Detection Simulation (section)

==Creating a Simulation==

Geant4 is a software platform used to simulate particle interaction with matter. It allows us to create a simulation of cosmic rays passing through a scintillator, and get the resulting data about the energy and behavior of the muons. CERN has several simulation examples that range from novice to advanced levels. Examining and editing these existing examples will prove to be valuable in setting up experimental simulations.  

===Modifying Geant4 Examples===

Geant4 has many basic examples of source code for simple geometry creation, particle gun set up, particle/matter interaction physics, and much more that will be utilized in this simulation.

'''1. Basic Geometry''' 

The B1 example simulation created two water filled figures being hit with a proton beam starting from random initial positions. The simulation was altered to create a single rectangular figure made of polystyrene to represent the scintallator. The beam was changed to muon particles starting at the same initial point. The examples can be found at: 

http://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch10s02.html

'''2. Basic Histograms/NTuples''' 

Example B4 includes samples of a runAction and an eventAction that define and fill histograms and ntuples.
 
The link to the source files can be found below: 

http://geant4.web.cern.ch/geant4/UserDocumentation/Doxygen/examples_doc/html/dir_947aedaba27c19df4f2d8e43055b6029.html

'''3. Advanced Scintillator'''

However, for a more advanced setup, CERN has an optical photon example that utilizes a PMT along with a scintillator to capture the deposited energy. 

The three directories to check are listed in the link below:

http://geant4.web.cern.ch/geant4/UserDocumentation/Doxygen/examples_doc/html/dir_eaaf04c8260eb39f9323c2b3410ba30e.html

=== Particle Simulation ===

'''1. Random Momentum Vectors'''

Following the initial setup of the program in Geant4, multiple things had to be changed in order to simulate an actual scintillator. One of these changes was to make the momentum vectors x,y, and z random to simulate how actual cosmic rays hit the scintillator. Before the edit was made, the particle beam shot in the manner shown below.

'''Helpful Geant4 Code :'''

Setting the momentum: ''fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0.,0.,1.));''

Now the Px, Py, or Pz components can be set and changed to augment the momentum in any orientation. 

'''Example 1: Same Angle'''

[[File:initialsimulation.png|center|frame|Simulation of 100 muons being shot at the scintillator at the same angle]]

Then, using a random number generator along with a time based seed, any number of particles could be shot at the scintillator, all at different angles from the starting point. The simulation of one hundred muons shot at different angles is displayed below. 

'''Example 2: Various Angles'''

[[File:randomsimulation.png|center|frame|Simulation of 100 muons being shot at the scintillator at varying angles]]

This change more accurately captures what occurs with the actual scintillator and was implemented to make it more realistic.

'''2. Random Muon Energies''' 

In order to better simulate the actual scintillator, the energy of the muon had to be changed from a set number to a randomly chosen number as well. Geant4 was altered to make the energy random for every trial. So, after this change was made, every single muon could be shot at random angles with random energies ranging from 0.35 GeV to 20 GeV. This range of energies was chosen from previous experiments that showed which energies were the best to use. Before the change was made, the simulation had a set, chosen energy. One of these simulations is displayed below. 

'''Helpful Geant4 Code :'''

Setting the energy: ''fParticleGun->SetParticleEnergy(6.*MeV);''

'''Example 3: Various Angles and Random Energies'''

[[File:setenergy.png|center|frame|Simulation of 10 muons being shot at the scintillator at varying angles with random energies]]