  Nearly a week went by. The lead capsule containing the stolen radioisotope had not been found. In fact, as far as Eddie knew, there had been no worthwhile clues on which to base a search. Curious as he was, Eddie still managed to keep from asking his father a lot of questions. Around home, Mr. Taylor had been thoughtfully silent. Eddie knew that his father must be very worried. Eddie gathered enough from the conversations between his parents to know that the search for the stolen isotope was still going on. In fact, it was pretty well known that FBI agents had arrived in Oceanview to lend a hand. Eddie hadn’t seen them, but several of his friends had. It was hard to keep secrets in a college town like Oceanview. The newspapers had temporarily dropped the story. After all, when the radioisotope had been stolen it had made a big story, but nothing more had happened, so there was nothing more to write about. There were still articles in the newspapers about the Acme Aircraft Company problem of the missing blueprints. Actually, it seemed to Eddie that the newspapers were making more of a mystery out of the missing blueprints than of the stolen radioisotopes. Perhaps that was because it had not yet been decided whether the blueprints had been stolen, destroyed by accident, or simply lost. In an aircraft plant, where thousands and thousands of plans are being used at all times, some carelessness is apt to occur. Eddie found it hard to believe that anyone could get careless with top-secret blueprints, yet such things did happen. Maybe the reason people remained curious about the missing blueprints was that everyone knew what a blueprint was. Even the word “radioisotope” meant very little to most readers. What they were and what they did were even less well known. Friday morning Teena came whistling up to the back door at Eddie’s house to see if he wanted to do anything. “Mom’s gone shopping,” Eddie said. “She’ll be back in a few minutes. Then maybe we could take the Geiger counter and—” His words were interrupted by the telephone ringing inside. “Be right back,” he said, hurrying into the house. His father was on the other end of the line. “Eddie,” he said, “there’s a dark-green notebook on my desk in the study. I forgot it this morning. Can’t get away from here, and I need it.” “I’ll bring it over, Dad,” Eddie volunteered quickly. “Good. I’ll be outside the botany building. Know where that is?” “Botany? Where they raise all the plants and stuff?” Eddie asked. “That’s right.” “I know where it is,” Eddie said. “Be there in five minutes.” He went into the study, got the notebook off the desk, and went back outside. “I’ve got to tear over to school with this notebook,” he explained to Teena. “That was my dad.” “I’ll go with you,” Teena said. “O.K.” It was only a few blocks to the college campus. Reaching the grounds, they took a short cut past the men’s gymnasium, crossed the athletic field, and arrived at the Botany Building. “I see Dad over there,” Eddie said, pointing. There were several men standing in a group in the small cultivated field which the botany department used to grow test plants of various kinds. Eddie and Teena picked their way carefully between the rows. “You made good time, Eddie,” his father said, taking the notebook. “Morning, Teena. Hope I didn’t interrupt any big plans.” “Oh, no, Mr. Taylor,” Teena said. “We weren’t doing anything special.” Eddie was about to turn and leave, when he noticed that several of the young men—students, no doubt—were wearing strange-looking, long, heavy gloves. “Why the gloves, Dad?” he asked. Mr. Taylor glanced up from the notebook. “We’re experimenting with radioactive tracers,” he said. “They’re weak—certainly not dangerous—but there’s no harm in taking a little extra precaution. The gloves are lead-lined and absorb any of the rays which might possibly be picked up from handling the plants.” “What are tracers, Mr. Taylor?” Teena asked. Eddie shot her a quick scowl. He doubted that his father wanted to be bothered with questions at the moment. Then Eddie noticed one of the students holding the wandlike probe—or diode—of a Geiger counter down close to the leaves of one plant. It seemed a strange thing to be doing. Who would prospect for uranium in plants. “That’s a good question, Teena,” Mr. Taylor said. “Glad to see you’re interested.” He turned and spoke to the student with the Geiger counter. “Jim, you want to explain to this young lady, and my son here, what tracers are?” Eddie smiled to himself. His father was the kind of a professor who believed his students should have the chance to use their knowledge whenever possible. “Maybe we should all listen to this,” Eddie’s father said to the others. They gathered around as the dark-haired student switched off the Geiger counter, swallowed a bit uncomfortably, and turned to face the outdoor classroom which Teena’s question had formed on the spot. “Well, er—” Jim began, addressing Teena, “a tracer is a radioactive isotope which we—well, send out on a journey, then follow it with a Geiger counter.” “I’m afraid that’s not too clear, Jim,” Mr. Taylor said. “Teena’s not an atomic scientist. Can you simplify it for her?” “Oh, I know what a radioactive isotope is, Mr. Taylor,” Teena said proudly. “You do?” Eddie’s father said in surprise. “It’s something—I think you call it an element—which they put in an atomic reactor, and—and cook it until it becomes radioactive. Kind of like a sponge soaking up water.” “Very good,” Mr. Taylor nodded, obviously impressed. “Eddie explained it to me,” Teena said, smiling, “but he didn’t say anything about tracers.” She turned her attention back to Jim, the student. “All right,” Jim said, seeming more at ease, “let’s look at it this way. Any radioisotope keeps shooting out rays. Of course, you can’t see the rays with your eyes. They’re almost too small to think about. But you can follow them with a Geiger counter.” He indicated the black metal instrument which he still held in his hand. “Well,” Jim went on, “say, for instance, that you wanted to know how fast a stream of water flows. You might toss in a rubber ball and time how long it takes to float a mile downstream. That would give you its speed. Or say you wanted to know which way its currents twist and turn. You might dump in a gallon of ink and watch it follow the currents. In a way, the ball and the ink are tracers. Not radioactive tracers, of course, but by watching how they act, you learn what you want to know.” “Let’s talk about radioactive tracers,” Eddie said eagerly. “You’re crowding me, bub,” Jim said, smiling. Everyone laughed. “How are we using tracers here, Jim?” Mr. Taylor prompted. “We’re testing the use of phosphate in plant growth,” the student explained. “We want to know what the plant does with it. Does a phosphate fertilizer merely feed the plant’s roots, or is it pulled up into the stems and leaves? And we want to know how quickly the plant absorbs it, if at all. Of course, we can’t see it, but if we make the phosphate slightly radioactive, then we have what we call a tracer. By using a Geiger counter, we can follow or trace its movement.” “Can you explain our method, Jim?” Mr. Taylor said. “Well, we spread a little of the radioactive phosphate around the plant,” the student said. “Soon the roots start taking it in.” “How do you know that, Jim?” Mr. Taylor asked. “We hold the Geiger counter to the root. If it starts clicking faster than usual, we know the root has absorbed some of the phosphate tracer. We also hold the Geiger counter over the stems and leaves. As the tracer works upward into the plant, the Geiger counter reacts to it. Here, let me show you how it works on this cotton plant.” Eddie and Teena moved over closer to the two-foot-high plant. Jim switched on the Geiger counter. Eddie saw the needle on the gauge flutter slightly, indicating the normal cosmic-ray background count. “Teena,” Jim said, handing her the earphones which were attached by a long wire to the Geiger counter, “you take these earphones. Now, I’ll pass the probe down close to the base of the cotton bush.” “What does the stick do?” Teena asked. Although Eddie had explained it to her, she seemed to feel that, as a pupil, she should ask some questions to help Jim out. “Stick? Oh, you mean the probe. Actually, it’s called a diode, but probe’s easier to remember. Anyway, the probe is a vacuum tube filled with a special kind of gas. Whenever invisible radioactive particles shoot through the probe and into the gas, the Geiger counter clicks, and the needle on the dial moves forward. The more rays shooting through the probe, the more clicks; the more clicks, the more radioactivity. That’s why Geiger counters are so useful in hunting for uranium. Uranium is very, very radioactive. If you happen onto some uranium ore, the Geiger counter really goes wild.” “We have a Geiger counter at home,” Eddie said eagerly. “Teena and I have gone uranium prospecting several times.” “Haven’t found any uranium,” Teena said, “but we’ve had fun trying. Whoops. There’s some clicking!” She put her hands up to the earphones. Jim had moved the probe down close to the stem of the cotton plant. “Good,” he said. “We mixed a little radioactive phosphate into the ground around the roots this morning. See, the Geiger counter shows that the phosphate tracer has already started moving up into the plant. Helps show how important phosphate is to plant growth, and how eagerly the plants absorb it.” “The plant sure looks healthy enough, all right,” Eddie said. “Right,” Jim said. “Now let’s see how far up into the plant the tracer has gone.” He moved the probe upward over the smaller twigs and leaves. On the lower leaves the Geiger counter kept clicking rapidly. Eddie watched the needle stay forward on the gauge. “See, the leaves have taken a lot of it in already,” Jim explained. Then, as he moved the probe farther up toward the top of the plant, the clicking diminished until only the familiar slow background count remained. “It quit,” Teena said. “Shows that the phosphate has only reached about half of the plant so far,” Jim said. “You see, with the tracer and the Geiger counter we can tell just how far it has gone and how long it has taken. We can even tell how much has been absorbed by comparing the amount of radioactivity in the leaves and stems of the plant to what we know was contained in the original tracer.” “Boy, that’s something!” Eddie exclaimed. “By adding tracers to some fertilizers,” Jim went on, “we found that the plant made no use of the fertilizer. The Geiger counter didn’t pick up any radioactivity in the plant. Meant wasted money to any farmer or gardener who used it. Now do you see what we mean by a tracer? See how radioactive tracers can be helpful?” “Oh, yes,” Teena said. “I do.” “I’ll bet if I had some of that tracer I wouldn’t lose so many things,” Eddie said. “I could paint a little on my marbles or sling-shot. Then I could always find them with a Geiger counter.” “You could, at that,” his father said. “And I wouldn’t be stepping on the marbles in my bare feet. But, of course, great care must be taken in handling radioisotopes, which is what tracers are.” Jim had warmed up to the subject, and wasn’t quite ready to drop it. “Tracers are used in many ways,” he went on. “They are used in medicine to locate diseased tissue which attracts and absorbs certain isotopes. A radiation-sensitive instrument, similar to a super Geiger counter, sniffs out the isotope and locates the damaged tissue. Then the doctor knows what to treat, or where to operate. Radioisotopes are used in various food tests. By watching the tracer with electronic gadgets, they can tell whether the food is a muscle builder, a bone builder, or what.” “You can make machine parts radioactive,” Mr. Taylor said. “Then by seeing how many radioactive particles are in the oil after the machine has been run, you can tell how much wear the machine has taken. Oh, there are hundreds of ways to use radioactive tracers. You might call them atomic signposts. Using a Geiger counter to read the signs, you are directed along the paths that lead to the answers of nature’s mysteries.” “Wow!” Eddie exclaimed. “Pretty flowery, at that, I guess,” his father said, smiling. “Well, anyway, Jim, you did a nice job of explaining it. Now, I think we’d better get back to our work. Thanks for bringing the notebook over, Eddie—and Teena.” The two young people turned and started back toward Eddie’s house. “Let’s go across the mall,” Teena suggested. “I haven’t been over here for a long time.” The mall, as it was always called, was a broad ribbon of lawn which stretched for more than a block down the center of the college campus. It was bordered on both sides by the many buildings which made up Oceanview College. Sidewalks laced back and forth across the mall. During class changes, the area swarmed with students. Now, as Eddie and Teena walked along the mall, only a few students sauntered around or sat loafing in front of the buildings waiting for their next class. Teena and Eddie walked past the library, the assembly hall, and the nuclear-science building. They were starting past the chemistry building, when Eddie tugged at Teena’s sleeve. “Look,” he said, pointing to the back of a man walking about fifty yards ahead of them. “Who’s that?” “Who’s who?” Teena asked. “You mean that man? Am I supposed to know him?” “I think I do,” Eddie said. “He sure looks familiar.” “How can you tell? All we can see is his back. Lots of backs look alike. He’s tall. Maybe he’s a basketball player. He looks older than most students, though. Why, his hair’s even a little gray, and—” “I’ve got it now,” Eddie interrupted. “The tall and kind of gray part. You know who? Simms. That fellow we ran into down at the cove last week.” “Well-ll, maybe,” Teena admitted thoughtfully. “We could tell for sure if he’d turn around. Anyway, I don’t see what difference it makes. Maybe he’s a student here. There are a lot of older students. Maybe he’s even a teacher. Lots of teachers fish on week ends. No reason to get excited.” “Who’s excited?” Eddie challenged. “Can’t a fellow ask—” “O.K., O.K.,” Teena said. “Anyway, there he goes into the chemistry building, so we’ll never know just who it was. And that’s the end of your mystery.” Eddie didn’t say anything. He walked along, busy with his own thoughts. Probably Teena was right. Why make a mystery of it? Even if the man were Simms, what difference would it make? Yet, why had Simms acted so strange and unfriendly that day. And for no reason Eddie could think of. There was also the memory of the strange metal tube which had been in the rowboat when the two men went fishing, and wasn’t there when they returned. There was no point in even mentioning it to Teena, but Eddie had a strangely uncomfortable feeling on seeing the man right there on the campus from which the secret radioisotope had been stolen recently. No, it really couldn’t mean a thing, Eddie told himself. Then, again, maybe it could. |
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