Author: Mohammadreza Zakeri (Zaki)
Contact: m.zakeri@eku.edu
Created: April 2025
Simulation Framework: Geant4
ActiveTargetSim is a Geant4-based simulation toolkit designed to study the generation, moderation, and stopping behavior of muons in layered target geometries. The simulation provides a testbed for understanding muon production and transport in dense materials and supports future R&D in muon-catalyzed fusion and applied particle beam technologies.
Key capabilities include:
- Configurable converter stacks with varying material thicknesses
- Longitudinal and radial muon diagnostics
- Target-layer indexing
- Visualization and filtering of muon-containing events only
Recent updates add a D-T gas region for potential fusion capture, along with event-level filtering to selectively visualize events with muon production.
- Modular detector geometry:
- Thin graphite target for initial proton collisions
- Gradient-thickness tungsten converter stack (e.g., 2.0 mm to 0.2 mm)
- Optional D-T gas capture region placed downstream
- Muon diagnostics with ROOT histograms:
- Muon creation energy
- Longitudinal and radial stopping locations
- Target volume index
- D-T region stop statistics
- Localized uniform magnetic field applied in D-T region
- G4SmoothTrajectory-based visualization for particle tracking
- Selective event retention for GUI: only muon-producing events are visualized
- Fully commented source with Doxygen support
Figure 1: Perspective view of the simulated detector. The upstream graphite target produces pions, which decay into muons. Muons traverse a gradient stack of tungsten converters, and surviving particles may enter a D-T gas region under a magnetic field for potential capture.
ROOT histograms are automatically generated for each run. Histograms include:
| Histogram | Description |
|---|---|
| MuonEnergy.pdf | Distribution of muon creation energies (MeV) |
| MuonStopZ.pdf | Z-position of muon stopping |
| MuonStopRadius.pdf | Radial distance from beamline at stop |
| MuonStopTarget.pdf | Target volume index where muon stopped |
| muonStopZ_DT.pdf | Z-position of muons stopped inside D-T region |
| muonStopR_DT.pdf | Radial stop distance inside D-T gas region |
mkdir build && cd build
cmake ..
makeMake sure Geant4 (with environment variables) is properly configured.
./active_target_simThis uses vis.mac to render the detector and muon tracks.
./active_target_sim run.macOutput is stored in muon_output.root by default.
If Doxygen is installed, you can generate full HTML and PDF documentation:
doxygen Doxyfile- HTML:
doc/html/index.html - PDF:
doc/latex/refman.pdf
Muon production begins with proton–nucleus collisions in the upstream graphite target, generating pions that decay in flight. The design uses high-density tungsten converters to moderate and stop muons.
New features include a D-T gas region with a localized magnetic field to explore the possibility of capturing muons in a fusion-relevant context. While full modeling of fusion reactions is outside current scope, this setup opens the door to downstream integration with fusion reaction models.
The simulation is well-suited for:
- Muon beamline studies
- Target design optimization
- Precursor designs for muon-catalyzed fusion systems
- Pion absorption vs. decay-in-flight remains a key design tradeoff. Many pions decay inside the tungsten converter layers, limiting escape probability.
- D-T fusion interaction modeling is not yet implemented. However, the current geometry and field setup support future addition of cross-section-based reaction tracking or yield estimation.
- Implement angular collimation or magnetic steering before D-T region
- Investigate pion decay lengths vs. absorption lengths in tungsten
- Extend detector with scoring planes or time-of-flight windows
- Add secondary reaction modeling (e.g., fusion triggers)
This project is open for academic and research use. Please cite or link to this repository if you use or modify the code.