The cold neutron source of the Munich Research Reactor (FRM)

In order to satisfy the growing need for low energy ("cold") neutrons in various fields of science the Munich Research Reactor (FRM) has recently been equipped with a cold neutron source. The facility is based on the secondary moderation of thermal reactor neutrons by subcooled liquid hydrogen being contained in a moderator chamber of V similar or equal to 0.9 l. Due to the conflicting: requirements of high transmission for low energy neutrons and sufficient mechanical strength the moderator chamber was fabricated in form of a thin-walled Al container being stabilized by a large number of internal Al support rods. It is installed within an evacuated beam tube in a distance of only few cm from the reactor core. Special safety considerations had to be taken into account due to the use of hydrogen within a nuclear reactor. The formation of an explosive mixture of hydrogen and oxygen within the reactor building is prevented by means of a multi-barrier system. In addition in case of serious malfunctions the total hydrogen content of the cold neutron source is exhausted automatically by He inert gas into the open air. The experimental areas are located outside the reactor building in a separate laboratory. First experimental setups, among these one for the neutron tomography of technical objects and a training experiment for students of the Technical University of Munich are in operation.