Robots and Empire (Page 128)

"But, then, how was the fission bomb ignited? Fission bombs existed before fusion bombs and if fission bombs required an ultrahigh temperature for ignition, as fusion bombs did, then there was nothing that existed before fission bombs that would supply a high enough temperature. From this, I conclude – even though the encyclopedia contained no information on the subject, – that fission bombs could be ignited at relatively low temperatures, perhaps even at room temperature. There were difficulties involved, for it took several years of unremitting effort after the discovery that fission existed before the bomb was developed. Whatever those difficulties might have been, however, they did not involve the production of ultrahigh temperatures. – Your opinion of all this, friend Giskard?"

Giskard had kept his eyes steadily on Daneel throughout his explanation and he now said, "I think the structure you have built up has serious weak points, friend Daneel, and therefore may not be very trustworthy – but even if it were all perfectly sound, surely this has nothing to do with the possible forthcoming crisis that we are laboring to understand."

Daneel said, "I plead for your patience, friend Giskard, and I will continue. As it happens, both the fusion process and the fission process are expressions of the weak interactions, one of the four interactions that control all events in the Universe. Consequently, the same nuclear intensifier that will explode a fusion reactor will also explode a fission reactor.

"There is, however, a difference. Fusion takes place only at ultrahigh temperatures. The intensifier explodes the ultrahot portion of the fuel that is actively undergoing fusion, plus some of the surrounding fuel that is heated to fusion in the initial explosion – before the material is blown explosively outward and the heat is dissipated to the point where other quantities of fuel present are not ignited. Some of the fusion fuel is exploded, in other words, but a good deal perhaps even most – is not. The explosion is powerful enough even so, of course, to destroy the fusion reactor and anything in its immediate neighborhood, such as a ship carrying the reactor."

"On the other hand, a fission reactor can operate at low temperatures, perhaps not much above the boiling point of water, perhaps even at room temperature. The effect of the nuclear intensifier, then, will be to make all the fission fuel go. Indeed, even if the fission reactor is not actively working, the intensifier will explode it. Although, gram for gram, I gather that fission fuel liberates less energy than fusion fuel, the fission reactor will produce the greater explosion because more of its fuel explodes than in the case of the fusion reactor."

Giskard nodded his head slowly and said, "All this may well be so, friend Daneel, but are there any fission power stations on Earth?"

"No, there aren’t – not one. So Undersecretary Quintana seemed to indicate and the encyclopedia seems to agree. Indeed, whereas there are devices on Earth that are powered by small fusion reactors, there is nothing – nothing at all – that is powered by fission reactors, large or small."

"Then, friend Daneel, there is nothing for a nuclear intensifier to act upon. All your reasoning, even were it impeccable, ends in nothing."

Daneel said earnestly, "Not quite, friend Giskard. There remains a third type of nuclear reaction to be taken into consideration."

Giskard said, "What might that be? I cannot think of a third."

"It is not an easy thought, friend Giskard, for on the Spacer and Settler worlds, there is very little uranium and thorium in the planetary crusts and, therefore, very little in the way of obvious radioactivity. The subject is of little interest, in consequence, and is ignored by all but a few theoretical physicists. On Earth, however, as Madam Quintana pointed out to me, uranium and thorium are comparatively common, and natural radioactivity, with its ultraslow production of heat and energetic radiation, must therefore be a comparatively prominent part of the environment. That is the third type of nuclear reaction to be taken into consideration."

"In what way, friend Daneel?"

"Natural radioactivity is also an expression of the weak interaction. A nuclear intensifier that can explode a fusion reactor or a fission reactor can also accelerate natural radioactivity to the point, I presume, of exploding a section of the crust – if enough uranium or thorium is present."

Giskard stared at Daneel for a period of time without moving or speaking. Then he said softly, "You suggest, then, that it is Dr. Amadiro’s plan to explode Earth’s crust, destroy the planet as an abode of life, and, in this way, ensure the domination of the Galaxy by the Spacers."

Daneel nodded. "Or, if there is not enough thorium and uranium for mass explosion, the increase of radioactivity may produce excess heat that will alter the climate, and excess radiation that will produce cancer and birth defects, and these will serve the same purpose – if a bit more slowly."

Giskard said, "This is an appalling possibility. Do you think it can really be brought about?"

"Possibly. It seems to me that for several years now just how many I do not know – humanoid robots from Aurora, such as the would-be-assassin – have been on Earth. They are advanced enough for complex programming and are capable, when needed, of entering the Cities for equipment. They have, it is to be presumed, been setting up nuclear intensifiers in places where the soil is rich in uranium or thorium. Perhaps many intensifiers have been set up over the years. Dr. Amadiro and Dr. Mandamus are here now to oversee the final details and to activate the intensifiers. Presumably, they are arranging matters so that they will have time to escape before the planet is destroyed."