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." "Why not report it right now?" Barby asked. "Good question. The answer is, we're not sure. Remember Carl Bradley was unsure enough to ask for help. If we got up before the UN and started hollering and it turned out to be plain water, we'd look pretty foolish." "I don't even know how we'd begin," Scotty muttered. "How do you start on a job like this?" "You'll start by being innocent tourists," Steve said. "You and Rick are students on a holiday, with Zircon, your uncle, as guide and tutor. You'll be interested in a number of things, including hunting. That will give you a good excuse for barging around the country if you have to. But you won't be able to decide what you want to hunt." Steve grinned. "You'll decide after you find out where you have to go. And you'd better learn about Asiatic game animals. For instance, if the trail takes you to Indonesia, you may want to hunt the hairy Sumatran rhinoceros. In the Philippines, you'll hunt timarau, which are a special breed of wild water buffalo. In China, around the coast, you can hunt tigers. In Malaya, if the trail does take you down to Singapore, you can hunt tapir. Same for Siam. In Indo-China you can hunt tigers. Inland in China, toward the Tibetan border, you'd better be hunting bharals." "That's a wonderful name," Barby said quickly. "What are they?"