Estimation of photoneutron yield in linear accelerator with different collimation systems by Geant4 and MCNPX...

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Engineering

Background:

• Linear accelerators (linacs) producing bremsstrahlung photon beams are standard for radiotherapy.
• Developing alternative radiation sources, like photoneutron sources, is crucial for advancing tumor treatments.
• Optimizing photoneutron generation requires careful consideration of linac electron beam energy, convertor materials, and geometry.

Purpose of the Study:

• To design and simulate a photoneutron source using different linac electron beam energies (6, 10, 15 MeV).
• To investigate the impact of convertor arrangements (with/without collimator) on neutron yield.
• To determine optimal parameters for tungsten convertor thickness and iron collimator dimensions for maximum neutron production.

Main Methods:

• Utilized Geant4 and Monte Carlo N-Particle eXtended (MCNPX) simulation codes for design and analysis.
• Studied two photoneutron convertor arrangements: without a collimator and with the convertor placed after the collimator.
• Investigated varying tungsten thicknesses and iron collimator dimensions (140 mm length, 5 mm × 70 mm aperture slit) to optimize neutron yield.

Main Results:

• Maximum photon intensities in tungsten increased with electron beam energy (0.73, 1.24, 2.07 photon/e at 6, 10, 15 MeV).
• Optimum tungsten thickness ranged from 0.8 mm to 2 mm, with no significant spectral increase from 6 to 15 MeV.
• BeO generated maximum neutrons at 6 MeV, while Beryllium (Be) showed peak neutron generation at 15 MeV; 30 mm was the optimal thickness for studied materials.

Conclusions:

• The study successfully designed a photoneutron source via simulation, identifying optimal parameters for enhanced neutron yield.
• Material choice (BeO vs. Be) and electron beam energy significantly influence neutron production.
• The optimized design provides a foundation for developing advanced radiotherapy sources.