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On the Accuracy and Efficiency of Condensed History Transport in Magnetic Fields in GEANT4

E Simiele*, L DeWerd , Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI


(Monday, 7/15/2019) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 1

Purpose: To investigate the accuracy and efficiency of electron transport in GEANT4 with and without a magnetic field present.

Methods: Fano cavity simulations were performed in GEANT4 version 10.02 and 10.04.p01 using the two multiple scattering (MSC) algorithms for two slab and one pseudo-ion chamber geometries. Magnetic field strengths ranging from 0T to 1.5T were investigated. An iterative approach was used to optimize the transport parameters to obtain agreement with theory.

Results: The electron step-sizes had to be severely restricted to obtain agreement with theory without a magnetic field present when using the Urban MSC model in GEANT4 v10.02. Minimal step length restrictions were needed to obtain agreement within 0.16% of theory for all simulation configurations that utilized the Goudsmit–Saunderson MSC model in GEANT4 v10.04.p01. Using the optimal parameters without a magnetic field present, the maximum deviation from theory was within 2% for all simulation configurations in the presence of a magnetic field except for two setups that exhibited discrepancies of up to 10.8%. This anomalous behavior was corrected by forcing single scattering within the detector gas volume. Further adjustments to the transport parameters resulted in agreement with theory at the 0.21% level.

Conclusion: Agreement with theory in the absence of a magnetic field can be obtained without significantly restricting the electron step size if the Goudsmit–Saunderson MSC model is used in GEANT4 v10.04.p01. The large discrepancies from theory observed for two simulation setups with a magnetic field were attributed to inaccurate energy loss sampling over a step. This problem can be mitigated by forcing single scattering within the detector gas volume; however, more work is needed to identify the cause of this anomalous behavior. This work has shown that GEANT4 can perform accurate electron transport with and without a magnetic field present without applying significant step-size reductions.


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