# Internal Generator¶

A primary particle 4-momentum and vertex ranges can be set with the gcard directives:

<option name="BEAM_P"   value="proton, 4.0*GeV, 20.0*deg, 10*deg"/>
<option name="BEAM_V"   value="(0, 0, -5)cm"/>


The above will generate a proton with:

• momentum between 3 and 5 GeV.
• θ between 10 and 30 degrees.
• ϕ between 0 and 360 degrees.
• vertex z between -5 and 5 cm.
• vertex radius between 0 and 0.1 cm.

Any gcard directive can be superseed by its corresponding command line. For example:

-BEAM_P="proton, 4.0*GeV, 20.0*deg, 10*deg"


# List of all particles¶

The following line will print on screen the list of particles (name and ids) that can be used by gemc:

-BEAM_P=show_all