spallation: (physics) a nuclear reaction in which a bombarded nucleus breaks up into many particles
physical entity: an entity that has physical existence
fuel-air explosive: a device consisting of a container of fuel and two explosive charges; the first charge bursts open the fuel container at a predetermined height and spreads the fuel in a cloud that mixes with atmospheric oxygen; the second charge detonates the cloud which creates an enormous blast wave and incinerates whatever is below