[Gate-users] Problem using the HounsfieldMaterialGenerator while applying custom ionisation potentials

[Aitkenhead Adam (RBV) NHS Christie Tr]

Hi,



I'm having difficulty applying custom ionisation potentials while using the HounsfieldMaterialGenerator in Gate 7.2.  The underlying problem is that custom ionisation potentials for elements don't seem to be inherited by subsequent materials.



For example: In Gate 7.2 the default ionisation potential for oxygen is 95 eV.  If I would prefer to use the potential (106 eV) listed in ICRU report 49, then I can set this as follows:



/gate/geometry/setIonisationPotential Oxygen 106 eV



The problem is that this new ionisation potential value is not used by Gate when it uses the Bragg additivity rule to calculate the ionisation potential for any materials containing oxygen.  For example, the ionisation potential of water remains at 68.998 eV, instead of increasing to 75.3 eV.



This isn't a problem for simple geometric simulations where a small number of materials are used, as the ionisation potentials for each material can be individually specified.  E.g.:



/gate/geometry/setIonisationPotential Water 75.3 eV



However, it is a problem when a simulation uses a CT image and materials are generated using the HounsfieldMaterialGenerator.  In this case, ionisation potentials are calculated based on the default element ionisation potentials - regardless of any custom element ionisation potentials that have been defined.



Does anyone have any suggestions - either for something I might have misunderstood, or for a workaround to allow custom ionisation potentials to be applied while using the HounsfieldMaterialGenerator?



Thanks,

Adam



adam.aitkenhead at christie.nhs.uk<mailto:adam.aitkenhead at christie.nhs.uk>
Christie Medical Physics & Engineering

The Christie NHS Foundation Trust
Manchester, UK

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