What are the experimental results of neutron -neutron scattering? I'm curious about does a neutron - neutron scattering (if such an experiment was carried out) is an in elastic process or is it accompanied by energy losses.
Additional question: What is the energy balance, if a neutron will be slowed down by a light beam?
 A: Free neutrons cannot be targets because of their limited lifetime. An enormous number of neutron-nucleus crossections and data exist. By using isotopic spin the neutron neutron crossections can be extracted from neutron-nucleus crossections. This presentation explores possibilities of  neutron on neutron experiments.
A: A neutron neutron collision would probably speed up the decay of one of the neutrons. Instead of 15 minutes it would be shorter. This is because neutron do not like being next to each other. The strong interaction sort of favors neutron neutron interaction less. However what the strong interaction does favor is the proton neutron interaction. So one of the neutrons will turn into a proton emitting an electron and an electron antineutrino. This might create deuterium. Or they might just bounce of of each other depending on the energy of the collision. If the energy is even higher(like around 3 Mev) then the neutron will turn into a proton as usual, however the other neutron will absorb the W- boson turning it into a Δ- baryon.
