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 [1] media:MedPhys.35.4308.pdf

GEANT4 Simulation

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

First Attempt

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

Second Attempt

• Use github.com to manage the simulation software

• The current geometry for the Bubble Chamber is in gdml and is shown below:

Using the ifarm or jlabl4 nodes

• Login remotely to the JLab gateway: $ ssh login.jlab.org
• Connect to either ifarm or Jlabl4:

1. $ ssh ifarm
2. $ ssh jlabl4

• Load Geant4 and ROOT Environments by running the following commands: (needed every login) (see [2] for more details)

1. $ source /site/12gev_phys/production.csh 1.1

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

> Common Environment Version: <1.1>  (Mon, 20 Oct 2014)
> Running as suleiman on ifarm1401
> OS Release:    Linux_CentOS6.5-x86_64-gcc4.4.7
> JLAB_ROOT set to:     /site/12gev_phys
> JLAB_SOFTWARE set to: /site/12gev_phys/1.1/Linux_CentOS6.5-x86_64-gcc4.4.7
> CLHEP   version: 2.1.3.1
> XERCES  version: 3.1.1
> QTDIR   version: system
> Geant4  version: 4.9.6.p03
> ROOT    version: 5.34.13
> GEMC    version: 2.1
> JANA    version: 0.7.2
> Build   version: 1.1
> EVIO    version: 4.0
> Banks   version: 1.0

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. $ cd BubbleEx
5. $ git pull (to update files from github)
6. $ mkdir build
7. $ cd build
8. $ use cmake (only if using JLab nodes)
9. $ cmake ..
10. $ make
11. $ 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:

To-do List

1. Geometry is in gdml format, need to get correct Radiator, Collimator, Beamline, PhotonDump geometry.
2. Add sweep magnet and electrondump geometry in gdml format.
3. Complete: 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, BubbleMother.gdml and all daughter files
4. The beamline STEP file will be ready very soon.
5. GEANT4 uses models that calculate wrong photo–nuclear cross sections (see above). 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.
   3. Could we not create a correct physicslist.cc in geant4 instead?

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

• Fluorine Cross Section:

1. ¹⁹F(γ,α)¹⁵N media:cs19Fga.txt (Eg (MeV), Cross Section (b))