A cold neutron source is a secondary moderator which locally reinforces the neutron flux by supplying cold neutrons. This is achieved by slowing down both fast neutrons coming from the core and thermic neutrons coming from the primary moderator through successive collision of incoming neutrons with atomic nuclei of a cold medium. The cold moderator technique of producing cold neutrons was experimented as early as 1957 at Harwell.
Horizontal Cold Source
The Horizontal Cold neutron Source (HCS) was built in 1987 to satisfy the huge demand for cold neutron beams.