Pulsed reactors as thermal neutron sources

Thermal neutrons are now accepted as one form of radiation needed by scientists to investigate the solid, liquid, and molecular states of matter. All thermal neutrons originate as fast neutrons, and these can start from burst reactors as well as steady-state reactors and accelerators. The pulsing or bursting of a reactor allows time-of-flight methods to be used for the thermal neutron experiments which realizes a gain over steady-state neutron source for the same average power. Since the maximum average power is one of the major limits to more intense neutron sources, pulsed reactors hold the potential for 1,000 times more peak power and thus effective flux and experimental capability than do the steady-state reactors. Examples of operating pulsed reactors used for thermal neutron research are the IBR-30 at Dubna and the booster at Harwell. Because of their advantages, other pulsed reactors have been proposed; while new ones continue to be proposed. As used for thermal neutron research, the past experience and future potential of pulsed reactors is reviewed. The position of fast burst reactors in the overall scheme of future thermal neutron sources is discussed. (auth.)