“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.