Abstract: The invention concerns a moderator material used for moderation of high-velocity neutrons, in particular of fission neutrons, to epithermal neutrons. The principal components of the moderator material are aluminum fluoride and aluminum metal, which have been formed into a dense composite substantially free of pores, wherein the material contains 20 to 50%-vol. of aluminum metal and 80 to 50%-vol. of aluminum fluoride. Further, the use of the moderator material in accordance with the invention in neutron capture therapy of cancer tumours is described, such as in boron neutron capture therapy (BNCT).