1- About registered processes, you can see them with /process/list
2- See
http://geant4-userdoc.web.cern.ch/geant4-userdoc/UsersGuides/ForApplicationDeveloper/html/TrackingAndPhysics/thresholdVScut.html
In short : there is no production threshold (aka setCut method) from neutron.
What you want is called Special Tracking Cut.
As said at the end of the above document, see examples/basic/B2