Neutron Jammer
From Cosmic Fate
An Neutron-Jammer is a device which suppresses nuclear fission reactions by blocking the movement of free neutrons (most forms of nuclear fusion, which do not rely on neutron emission, would be unaffected by an Neutron-Jammer). A side effect is their ability to disrupt radio waves as well, which restricts the range of radar and conventional communications, as such they can be counted as a form of electronic countermeasures as-well.