New neutron sources.

This paper describes the latest developments in neutron sources developed for fast neutron therapy. Two approaches have been taken using cyclotrons and D-T generators. For cyclotrons the proton on beryllium reaction is now preferred since smaller cyclotrons for a given neutron penetration can be used. Optimization of target thickness and filtration is necessary to obtain maximum beam penetration. D-T generators have been developed either as multi-beam accelerators or using ultrapure techniques to obtain maximum neutron output.