Simulations and Backgrounds

GEANT4 vs. Experimental Data

• Benchmarking of monte carlo simulation of bremsstrahlung from thick targets at radiotherapy energies

B. A. Faddegon, M. Asai, J. Perl, C. Ross, J. Sempau, J. Tinslay, and F. Salvat. Med. Phys. 35 (2008) 4308 media:MedPhys.35.4308.pdf

GEANT4 Geometry

• Using github.com to manage the simulation software: /group/bubble/

• The current geometry for the Bubble Chamber is in gdml and is shown below with the outer shell visible and hidden:

• The example geometry of the beamline and bubble is shown here:

• To-do List:

1. Continue to encode the geometry in GDML, an XML based format that GEANT4 reads in.
2. Include the Bubble Chamber geometry using the Bubble Chamber STEP file (change .txt to .stp): media:BubbleChamber.txt.
   1. Geometry has been created and is on github, BubbleChamber.gdml
   2. Correct the materials list
3. The beamline STEP file will be ready very soon. When? Last file recieved was BubbleChamber again 6_24_2014.
4. GEANT4 uses models that calculate wrong photo–nuclear cross sections (see below). GEANT4 does not allow for user’s cross sections. What to do?
   1. Use GEANT4 to produce the photon spectra impinging on the superheated liquid.
   2. Fold the above photon spectra with our cross sections in stand-alone codes.

• GEANT4 Photon-Inelastic Model: CHIPS Gamma Nuclear has this cross section for our reaction:

• Quick start for the simulation: media:G4_BubbleEx_README.txt. There is also a README file that comes with the example.
• Bubble Chamber GEANT4 Example (change .txt to .tar): media:BubbleEx96.txt

Compiling/Running Simulation (BubbleEx)

• Using the ifarm or jlabl1 nodes
• Login remotely to the JLab gateway: $ ssh login.jlab.org
• Connect to either ifarm or Jlabl1:

1. $ ssh ifarm
2. $ ssh jlabl1

• Load Geant4 and ROOT Environments by running the following commands: (needed every login)

1. $ setenv JLAB_VERSION production
2. $ setenv JLAB_ROOT /site/12gev_phys
3. $ source ${JLAB_ROOT}/${JLAB_VERSION}.csh

• Should see a short list of programs such as ROOT and Geant4 listed

• Compiling the simulation
• Simulation is available at https://github.com/JeffersonLab/BubbleEx
• Create directory for simulation:
• On JLab nodes can use /group/bubble/ directory:

1. $ mkdir /group/bubble/<user>
2. $ cd /group/bubble/<user>
3. $ git clone https://github.com/JeffersonLab/BubbleEx.git
4. $ git pull (to update files from github)
5. $ mkdir build
6. $ cd build
7. $ use cmake (only if using JLab nodes)
8. $ cmake ..
9. $ make
10. $ cd ..

• Running the simulation
• In the install directory

1. $ build/BubbleEx (remember to run the source command before running)

• Terminal will list what has been loaded and then display output command box
• In session run:

1. $ /vis/open OGL
2. $ /run/beamOn 100

• Initial run of the simulation is shown:

Relevant Cross Sections

• Photo-Nuclear Cross Sections:

1. ¹⁶O(γ,α)¹²C media:cs16Oga.txt (Eg (MeV), Cross Section (b))
2. ¹⁷O(γ,α)¹³C media:cs17Oga.txt
3. ¹⁸O(γ,α)¹⁴C media:cs18Oga.txt
4. ¹⁴N(γ,p)¹³C media:cs14Ngp.txt

• Neutron Elastic Cross Sections:

1. ¹⁶O(n,n) media:cs16Onn.txt (En (MeV), Cross Section (b))
2. ¹⁴N(n,n) media:cs14Nnn.txt