Rick explained on the way back to the farm. "There are four main kinds of radioactivity. They're called alpha, beta, gamma, and neutrons. Our sample has alpha and gamma. That means it doesn't come from either bomb debris or from a reactor, because fission takes place in both, and there is almost always beta activity as well as gamma in the products of fission. But some isotopes of uranium and thorium have little beta, with some alpha and gamma, so Baxter concluded we had powdered uranium ore. There are many kinds of ore. Pitchblende is the best, but carnotite, which is a gray rock with yellowish streaks, is also good ore. Got it now?"
Jan Miller asked, "How do you know all this, Rick?"
The boy chuckled. "From associating with your father and mine, not to mention Weiss, Zircon, and the other scientists. They talk and Scotty and I listen. Also, Dad has a lot of books on atomic energy, and some of them are simple enough for me to read."
The Sky Wagon was over the Miller farm in a very short time, but before landing Rick made a swing of the area. The young people readily identified the mine and picnic grounds, and Rick pointed out the quarry into which he had tumbled.
Scotty said, "Something's been bothering me. If the Frostola man is new in this area, how could he have known the terrain well enough to lead us on that wild-goose chase?"
"He's new, but not that new," Rick pointed out. "He's had weeks in which to study the lay of the land. Besides, he does his haunting at night—if he's the one—and he roams the fields near the mine. He must know his way around."
"You're right," Scotty assented. "Now tell me this: why did he take the cement bags?"
"To keep us from finding out that they didn't contain cement," Rick said. "It has to be the reason. That means he knew about the bags, and maybe he even buried them. He didn't bury them deep, because who would think anything of a bunch of cement bags, except a pair like us? Then, when he saw they had turned up, he collected them and took them somewhere else. The bags we found this morning may even be the same ones, although I think they're a second set. He'd hide the first set better than he did at first."
"Your language is confused, but I get your meaning." Scotty grinned. "Okay, detective. Set us down. It's suppertime."
Rick swung into his landing pattern. "Anyway, we've made progress," he commented with satisfaction. "We started with just a ghost. Now look what we've got!"