minimc_src

MiniMC source cfg-strings

Three MiniMC neutron source types are currently available, differing only in the way they generate the initial position and direction of the neutrons. Other parameters are common to all sources, including those related to neutron energies or how many neutrons to generate.

Quick usage examples

• "constant;wl=1.8;z=-0.1"

  1e6 neutrons are generated with a wavelength of 1.8Aa as (x,y,z)=(0m,0m,-0.1m) with direction (0,0,1).

• "constant;ekin=0.001-0.1;x=2;z=-0.1;ux=0;uy=1;uz=1"

  1e6 neutrons are generated at (x,y,z)=(2m,0m,-0.1m) with direction (0,1,1) and wavelengths are sampled uniformly in the interval [0.001eV,0.1eV].

• "circular;wl=1.8;z=-0.1;r=0.1;n=1e8"

  1e8 neutrons are generated with a wavelength of 1.8Aa with direction (0,0,1) and with a position sampled uniformly on the disk with center (0m,0m,-0.1m) and normal (0,0,1).

• "isotropic;ekin=0.025+-0.001;n=10000"

  10000 neutrons are generated at the point (0m,0m,0m) with an isotropically sampled direction and an energy sampled from a log-normal distribution with mean 0.025eV and variance (0.001eV)^2.

Parameters common to all sources

For all sources, the parameter "n" (default 1e6) is used to specify the number of neutrons to generate.

Parameters "ekin" and "wl" are also common to all sources, and allow for a flexible specification of the generated neutron energies, as shown by these examples:

• "ekin=0.025"

  All neutrons are generated with an energy of 0.025eV.

• "ekin=0.025-0.05"

  Neutron energies are sampled uniformly in the interval [0.025eV,0.050eV].

• "ekin=0.025+-0.001"

  Neutron energies are sampled from a log-normal distribution with mean 0.025eV and RMS 0.001eV.

• "ekin=thermal:77K"

  Neutron energies are sampled from a thermal (Maxwell) distribution at 77K.

• "wl=1.8"

  All neutrons are generated with a wavelength of 1.8Aa.

• "wl=1.8-5"

  Neutron wavelengths are sampled uniformly in the interval [1.8Aa,5Aa].

• "wl=1.8+-0.01"

  Neutron wavelengths are sampled from a log-normal distribution with mean 1.8Aa and RMS 0.01Aa.

Specific sources available

The available sources are:

• "constant":

  A source which always provide the same position and direction of the initial neutron.

  Parameters:

  • ekin, wl, and n : Explained above.
  • x (default "0") : x coordinate of position [m].
  • y (default "0") : y coordinate of position [m].
  • z (default "0") : z coordinate of position [m].
  • ux (default "0") : x coordinate of direction.
  • uy (default "0") : y coordinate of direction.
  • uz (default "1") : z coordinate of direction.

• "circular":

  A source which allows modelling of a beam of uniform circular cross section. Specifically, all neutrons are generated with a fixed direction, and with a position sampled uniformly within a disk of radius r. The center of the disk is configurable, while its normal is always parallel to the direction of the neutrons.

  Parameters:

  • ekin, wl, and n : Explained above.
  • x (default "0") : x coordinate of disk center [m].
  • y (default "0") : y coordinate of disk center [m].
  • z (default "0") : z coordinate of disk center [m].
  • ux (default "0") : x coordinate of direction.
  • uy (default "0") : y coordinate of direction.
  • uz (default "1") : z coordinate of direction.

• "isotropic":

  A source which emits neutrons isotropically from a particular point or spherical surface.

  Parameters:

  • ekin, wl, and n : Explained above.
  • x (default "0") : x coordinate of position [m].
  • y (default "0") : y coordinate of position [m].
  • z (default "0") : z coordinate of position [m].
  • r (default "0") : Signed radius of sphere. Neutrons are always first placed on the point (x,y,z) and assigned an isotropically sampled direction. If r!=0, the position is then translated a distance of -r along that direction.