Tactical nuclear weapons are those whose payload is typically less than five kilotons. These weapons are designed to be used in close range of friendly troops, and attempt to minimize collateral damage. One method of this involves "boosting" the radiation effects of a nuclear blast, which reduces the destructive fireball. Such bombs have the added benefit of irradiating tanks and other instruments of war. During the blast any crew of such a vehicle would be instantly killed from radiation 10 times stronger than the documented "lethal" dose. Should that vehicle be manned within the next 24-48 hours, the new crew would suffer the same fate. While fears of blurring the line between conventional and nuclear warfare have restricted deployment of these weapons, many world powers continue to investigate the concept of battlefield nuclear weapons.