|Message: Re: about step limitation in Hadrontherapy||Not Logged In (login)|
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Are you using the PhysicsList as distributed in the hadrontherapy example, with one of the modelling options it provides?
If so, your use case of particle transport at the nanometer scale is outside the scope of applicability of the physics models considered in that example. Concerning electrons, the lowenergy models should be reliably used down to 250 eV at most; you may still use them below this suggested threshold, but the accuracy of the simulation would be substantially degraded, due to the inadequate scheme of assumptions at the basis of condensed-random-walk Monte Carlo transport. Therefore, the simulation results you may obtain by limiting the stepping or lowering the secondary production threshold with respect to the setting in the hadrontherapy example should be considered with caution.
Geant4 models capable of dealing with micro- and nano-dosimetry simulation are under development; the first set, applicable to interactions in water, has been released in Geant4 9.1 (reference S. Chauvie et al., Geant4 physics processes for microdosimetry simulation: design foundation and implementation of the first set of models, IEEE Trans. Nucl. Sci., vol. 54, no. 6, pp. 2619-2628, Dec. 2007).
An example specific to the usage of these new processes is in preparation. Should you need any help at using them, if they are appropriate to your use case, please feel free to further contact us.
Maria Grazia Pia
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