Rick thought furiously and came up with what he hoped was the answer. "I think it's that isotopes aren't as stable as the basic elements. Some are pretty stable, but some are pretty shaky. That's why some of the isotopes of uranium can be split wide open in a chain reaction to make an atomic bomb, and ..."
A chill ran through him. His mouth opened. He knew! He knew why heavy water had Steve Ames all excited. He choked:
"Hydrogen bombs!"
Scotty and Barby gasped. Steve Ames and Hartson Brant smiled.
"It's true that one of the possibilities in building a hydrogen bomb concerns deuterium," the scientist said. "But I scarcely think that's the case here. How about it, Steve?"
"Possible, but extremely improbable," Steve agreed. "What I'm most interested in is a use for heavy water Rick hasn't mentioned. Know what a nuclear reactor is, Rick?"
Rick nodded. "It's what the newspapers usually call an 'atomic pile.' We have quite a few in this country, I think. The Atomic Energy Commission said quite a while ago that they used a nuclear reactor with uranium as a fuel to make plutonium, which is the artificial element that can be used in atomic bombs. Besides uranium itself, that is."
"That's right. What I'm interested in is the fact that heavy water can be used as a neutron moderator in a reactor."
Rick looked blank. Steve was talking way over his head. Hartson Brant saw his son's bewilderment and explained: "You've probably heard that the uranium in a reactor is encased in blocks of graphite, which is simply carbon, Rick. It prevents the neutrons from the uranium from simply running wild. Well, heavy water can be used for the same purpose."
"Exactly," Steve said. "So you see, I'm not afraid of the possibility of hydrogen bombs as much as I am of the possibility that somewhere in Asia is a nuclear reactor. Until we get international agreement on atomic weapons, we simply have to keep track of atomic developments everywhere for our own protection. If there's a new country going in for atomic research, and it can build a reactor, it might also be able to build an atomic bomb. Now, don't forget I said heavy water is a legitimate industrial product. We certainly can't object to a nation's manufacturing it. We wouldn't want to. But when it turns up in an odd corner of the world, I think we'd better find out why. If it's a peaceful reason, we'll mark it down and then forget it. If not, we'll make a report to the United Nations."