19) Where reactor operation is designed with fast neutrons such as in reactors using highly enriched fuel, the moderator used is

20) In a diesel engine, the duration between the time of injection and ignition, is known as

21) The detonating tendency in petrol engines increases with increase of compression ratio.

22) Each fission of U₂₃₅ produces on the average __________ fast neutrons as a product of reaction.

23) Reactors for propulsion applications are designed for