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

• Bubble Chamber GEANT4 Example (change .txt to .tar): media:BubbleEx.txt
• Quick start for the simulation is provided in the README file included in the example

• The example geometry is shown here:

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

• To-do List:

1. Use github.com to manage the simulation software.
2. Encode the geometry in GDML, an XML based format that Geant4 reads in.
3. Include the Bubble Chamber geometry using the Bubble Chamber STEP file (change .txt to .stp): media:BubbleChamber.txt.
4. A STEP file for the beam line 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.

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