Particle-Matter Interactions
Use the Particle-Matter Interactions node to model the propagation of energetic ions through solid material. The Ionization Loss and Nuclear Stopping subnodes are available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu. In order to model the interaction of particles with the target material, at least one subnode must be added.
Target Material Properties
By default, the Density ρ (SI unit: kg/m2) is taken From material. For User defined enter another value or expression.
Enter a value or expression for the Atomic mass A (SI unit: kg). The default value is 28.0855 amu, the relative atomic mass of silicon. Then enter a value or expression for the Atomic number Zm (dimensionless). The default value is 14.
Particle Properties
Enter a value or expression for the Atomic number Zp (dimensionless). The default value is 1. The particle atomic number is used to define screened Coulomb potentials for the Nuclear Stopping node.
Cutoff Energy
Select the Stop particles with energy below cutoff to cause particles to stop moving when their energy is less than a specified value. This check box is selected by default. Then enter a value or expression for the Cutoff energy Ec (SI unit: J). The default value is 8.6 eV.
In general, the Stop particles with energy below cutoff check box should always be selected if it is possible for ions in the material to approach extremely low energies. With the built-in ionization loss and nuclear scattering models, accurate data is not available for energies significantly less than the default value, 8.6 eV.
Accumulated Variables
In this section the following check boxes are shown:
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Absorbed dose
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Absorbed dose from ionization losses
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Absorbed dose from nuclear stopping
Selecting a check box causes domain variables to be defined, to compute the total absorbed dose in grays (Gy) and the dose equivalent in sieverts (Sv) at the particles pass through the domain. The check box called Absorbed dose adds the doses from both of the supported subnode types: Ionization Loss and Nuclear Stopping.
Because the volumetric quantities defined by these check boxes are accumulated variables, the same rules apply to them as other types of accumulator. The accumulated variable uses constant shape functions that are uniform within each domain mesh element and may be discontinuous between elements.
By default, all of these check boxes are cleared. If any of the three check boxes are selected, enter a value or expression for the Quality factor Q (dimensionless). This quality factor is used to convert between absorbed dose and dose equivalent, either of which can be plotted. The default is 1. If the model particles represent a heavy species such as protons or alpha particles, then a larger value of Q should be entered.
Affected Particles
Use this section to determine which particles are subjected to the particle-matter interaction. By default, all particles in the model are affected. The settings are described for the Force node.