Particle Sources

The Particle Sources element contains all particle sources of the simulation. All particle sources contain the same options, but are differentiated based on the specification type. Multiple particle sources may be used in a single simulation.

Source Types

point A point source can specify the x,y and z coordinates of the point. All particles will emit from this point. The point is visualized by a sphere. The radius of this sphere is controlled by the representationRadius property, it has no effect on the simulation.

surface To create a surface source first create a Sphere, Box, or Cylinder CSG object. It must then be assigned the Material Source to designate that it is being used as a particle source. At this time any Cylinder or Box source must be axis-aligned. All particles will emit from the surface.

volume To create a volume source first create a Sphere, Box, or Cylinder CSG object. It must then be assigned the Material Source to designate that it is being used as a particle source. At this time any Cylinder or Box source must be axis-aligned.

plane A plane source will emit particles from the 2D plane specified. The available types of planes are.

  • xy plane This is a rectangular plane on the xy axis.
    • offset The z coordinate of the plane.
    • xMin The lower x coordinate of the plane.
    • xMax The upper x coordinate of the plane.
    • yMin The lower y coordinate of the plane.
    • yMax The upper y coordinate of the plane.
  • xz plane This is a rectangular plane on the xz axis.
    • offset The y coordinate of the plane.
    • xMin The lower x coordinate of the plane.
    • xMax The upper x coordinate of the plane.
    • zMin The lower z coordinate of the plane.
    • zMax The upper z coordinate of the plane.
  • yz plane This is a rectangular plane on the yz axis.
    • offset The x coordinate of the plane.
    • yMin The lower y coordinate of the plane.
    • yMax The upper y coordinate of the plane.
    • zMin The lower z coordinate of the plane.
    • zMax The upper z coordinate of the plane.
  • xy ellipsis An ellipsis (or circle) on the xy plane
    • rX The x-radius of the ellipsis.
    • rY The y-radius of the ellipsis.
    • x The center of the ellipsis on the x axis.
    • y The center of the ellipsis on the y axis.
    • z The center of the ellipsis on the z axis.
  • xz ellipsis An ellipsis (or circle) on the xz plane
    • rX The x-radius of the ellipsis.
    • rZ The z-radius of the ellipsis.
    • x The center of the ellipsis on the x axis.
    • y The center of the ellipsis on the y axis.
    • z The center of the ellipsis on the z axis.
  • yz ellipsis An ellipsis (or circle) on the yz plane
    • rY The y-radius of the ellipsis.
    • rZ The z-radius of the ellipsis.
    • x The center of the ellipsis on the x axis.
    • y The center of the ellipsis on the y axis.
    • z The center of the ellipsis on the z axis.

Source Properties

number of particles per event This is the number of particles to emit for each event.

particle type The type of particle to emit. The available particles are:

  • electron
  • proton
  • neutron
  • positron
  • alpha
  • gamma
  • ion
    • atomic number Atomic number of the ion.
    • nucleon number Number of nucleons in the ion.
    • charge Charge of the ion.
    • nuclear excitation Excitation of the ion.

Angular Dist The type of angular distribution of the particle source.

  • Omnidirectional With an omnidirectional angular distribution the fluence for each direction is proportional to the cosine of the angle between the source direction and local noraml of the surface.

    • min theta The minimum angle, 0 degrees corresponds to the -Z axis.
    • max theta The maximum angle, 180 degrees corresponds to the +Z axis.

    If Computed Normalization is selected, and the source is not a point, the angular distribution factor is calculated as \(\frac{1}{4}*(\sin^{2}(max theta) - \sin^{2}(min theta)\)

    If the source is a point, the angular distribution factor is \(\frac{1}{2}*(\cos(min theta) - \cos(max theta)\)

  • Isotropic If emitting from a rectangular slab or plane, the final distribution of particles will not in fact be isotropic as the angle of emission will impact the resulting fluence.

    • min theta The minimum angle, 0 degrees corresponds to the -Z axis.
    • max theta The maximum angle, 180 degrees corresponds to the +Z axis.

    If Computed Normalization is selected, the angular distribution factor is 1.0

  • Beam1D A beam1D source will feature a uniform dispersion angle around the beam. The beam angular distribution is only available with planar sources.

    • dispersion angle The dispersion angle of the beam.
    • beam direction Either positive or negative, this will send the particles on the corresponding axial direction.

    If a Beam1D angular distribution is used, Computed Normalization cannot be used.

Energy Spectrum The energy spectrum of the particle source. Options are

  • MonoEnergetic

    • mono Energy of the source.
    • units Units of the energy source specified.
    • fluence Used in normalization calculations if Computed Normalization is selected.

    If using computed normalization, the energy normalization factor will take the form \(\frac{gradient}{2}max^{2}+intercept*max-\frac{gradient}{2}min^{2}+intercept*min\)

  • Linear The linear distribution takes the form y = gradient * energy + intercept

    • min Minimum energy.
    • max Maximum energy.
    • units Units of the energy source.
    • intercept Intercept of the linear curve.
    • gradient The source strength multiplier.

    If using computed normalization, the energy normalization factor will take the form \(\frac{gradient}{2}max^{2}+intercept*max-\frac{gradient}{2}min^{2}+intercept*min\)

  • Power Law The power law distribution takes the form y = gradient * energy ^ alpha

    • min Minimum energy.
    • max Maximum energy.
    • units Units of the energy source.
    • alpha The exponential of the energy distribution.
    • gradient The source strength multiplier.

    If using computed normalization, the energy normalization factor will take the form \(\frac{gradient}{(alpha + 1)} * max^{alpha + 1} - \frac{gradient}{(alpha + 1)} * min^{alpha + 1}\)

  • Exponential The exponential distribution takes the form \(y = coefficient * e ^(\frac{energy}{eZero})\)

    • min Minimum energy.
    • max Maximum energy.
    • units Units of the energy source.
    • coefficient The source strength multiplier.
    • eZero Base value of the exponential.

    If using computed normalization, the energy normalization factor will take the form \(-coefficient*eZero*e^{\frac{-Emax}{eZero}} + coefficient*eZero*e^{\frac{-Emin}{eZero}}\)

  • 2 Column File The 2 column file needs to be arranged in order of Energy|Differential Fluence increasing from row to row.

    The integral flux is given in units of particles/cm^2/second^2, while the differential flux is given as particles/cm^2/second^2/MeV

    • file name Name of the file.
    • max integral flux Used in normalization calculations if Computed Normalization is selected.
    • min integral flux Used in normalization calculations if Computed Normalization is selected.
    • interpolation type Interpolation between points of the file.
      • linear
      • power-law
      • cubic spline
      • exponential

    If using computed normalization, the energy normalization factor is the difference between the max and min integral flux. These values need to be specified directly, as various models will give slightly different values.

  • Gaussian This gives a guassian energy distribution, and does not allow for a computed normalization to be used.

    • energy center Center of the gaussian distribution.
    • sigma The standard deviation of the gaussian distribution.
    • units The units of the energy center.

Normalization

With either the Computed or Manual normalization factors, the normalization is itself calculated in the same way. This is normalization to a current going through the primary surface, multiplying the final results by surfaceArea/Nparticles * (energyNormalizationFactor * angularNormalizationFactor)

Where surfaceArea is the surface area of the source, and Nparticles is the number of particles emitted by the source.

  • No Normalization If selected the source will not be normalized.
  • Computed Normalization If computed normalization is used, the normalization factors are calculated as described in the energy spectrum and angular dist.
  • Manual Normalization With manual normalization the angular and energy normalization factors are specified directly.