“Those are tiny,” Thornton said. “Small enough to be injected through a syringe. And they’re generally palladium-103 or iodine-125. They’re also very, very weak compared to this. You wouldn’t want your prostate to get cooked like Novak’s gut, would you?” Emert shuddered. “Speaking of medical isotopes, though,” Thornton went on, holding up an index finger to indicate that he found this an interesting sidelight, “one of the uses of iridium-192 is to create medical isotopes like palladium and iodine.” I was losing track of all the isotopes, but Thornton seemed to have no trouble keeping them straight.
“One isotope creating another,” I said. “The atomic ripple effect?”
“More like billiard balls,” Thornton said. “All those protons and neutrons and electrons and photons ricocheting around on the pool table of the universe. I’m amazed everything hangs together as well as it does. One of these days, seems like, the cosmic cue stick will strike, all the balls will scatter, and then they’ll drop, one after another, into the corner pockets and side pockets of oblivion.”
“Why, Agent Thornton,” I said, “you’re a poet.”
He laughed. “Nah, it’s just smoke and mirrors. I’m desperately trying to distract you from the realization that I don’t really understand this stuff.”
Smart, poetic, and self-deprecating, to boot — no wonder Miranda seemed to be taking a shine to him. “So this iridium-192,” I said. “UT Hospital has a pretty big nuclear-medicine department. Is there any chance this iridium-192 might have come from there?”
“Yes they are, but no it couldn’t,” he said. “They do create radioisotopes there. They’ve got a cyclotron right above the morgue that Ernest Lawrence would’ve given his left nut for. But UT doesn’t use iridium-192 sources.”
“Then who does?” Emert and I asked the question at the same time.
“I’m so glad you asked,” he smiled. He tapped the cursor pad on his computer, and a washed-out blue slide appeared on the white wall behind him. Thornton pointed at the fluorescents overhead, and Emert killed the lights. When he did, the FBI logo blazed from a deep blue background.
The intro slide faded to black, and then another image faded up. It was a nuclear power plant, its iconic cooling towers sending billows of steam skyward. “The pressure vessel and the cooling-water pipes in a reactor like this are about six inches thick,” he said. “Those components have to be strong as hell, and so do the welds that hold them together.” He flashed through a series of ghostly images, X-ray-like pictures of fissures and streaks and bubbles in metal tubes; cracks and voids in seams. “These are radiographs of pipes and welds in a nuclear plant,” he said. “And this is the camera that took them.”
The next slide showed a four-wheel dolly loaded with an instrument the size and shape of a footlocker. “This is an industrial radiography camera,” Thornton said. “Think of it as a turbo-charged big brother to a medical X-ray machine. It uses gamma radiation rather than X-rays, because gamma has higher energy and can penetrate steel much better.” He flashed to a close-up view of the box on the cart; enlarged, it looked like a footlocker with dials and cables in one end. “This particular camera uses cobalt-60, not iridium, as the gamma source; this is three hundred curies, which is a good bit hotter than what we’re dealing with.”
I recalled a tour I’d taken once of TVA’s Watts Bar Nuclear Plant, located downstream from Knoxville. “Nuclear plants have pretty tight security,” I said. “Wouldn’t it be pretty tough for Bubba to wheel that cart out the gate and wrestle it into the bed of his pickup?”
“You’re right. So who else uses radiographic cameras?” He flashed up a series of slides showing mammoth industrial complexes — sprawling, three-dimensional mazes of pipes and girders and steel exhaust stacks filled the wall. “Petroleum refineries. Chemical plants. Just like nuclear plants, they’re pumping nasty stuff at high temperatures and pressures, through heavy-gauge pipe. So are these guys.” He flashed rapidly through several slides showing pipelines — the Alaskan oil pipeline, a water pipeline in the West, a natural-gas pipeline. “Every pipeline company in the world worries about weld failure,” he said. “Right now, as we sit here, there are dozens of technicians — maybe hundreds — scurrying around the country taking radiographs of power plants and refineries and chemical plants and pipelines.” He paused to let that sink in. “And a lot of them aren’t using the big rig on the cart. A lot of them are using gadgets like this.” He tapped the cursor again.
I found myself looking at the legs and waist and dangling left arm of a man photographed in mid-stride. Clutched in his hand was a bright yellow gizmo whose size and shape reminded me of a construction worker’s lunch box — the black, barn-shaped kind, with a rectangular base to hold the sandwich and apple and chips and cookies, and a cylindrical top to hold the thermos. A heavy, pipe-fitting-looking extension jutted from one end of the yellow box, though, and the universal warning sign for radiation was emblazoned prominently on the side. “This camera is handheld, obviously,” said Thornton. “Very compact; very portable. The case is rugged enough, with enough shielding, to allow a two-hundred-curie iridium source to be legally transported in any vehicle.”
He flashed to another picture, this one showing a boxier gadget topped by a tubular handle. This picture showed considerably more detail. “Another handheld radiography camera,” said Thornton, “the RadioGraph Elite, made by Field Imaging Equipment Company, in Shreveport, Louisiana.” He pulled a laser pointer from his shirt pocket and traced the instrument’s rectangular outline with the dot of light. “This is fourteen inches long by five inches square — the size and shape of those newspaper boxes people out in the country put underneath their mailbox. The case is stainless steel; inside the case is a shielding block of depleted uranium. It’s small, and you can carry it by that handle, but you wouldn’t want to carry it far, because that sucker weighs fifty pounds. The manufacturer calls it portable; I’d call it luggable.”
He replaced the photograph with a cutaway drawing of the camera. Most of the interior consisted of the block of depleted uranium. A hollow tube or tunnel traced a shallow S-curve through the center of the block, and Thornton ran the laser dot back and forth along a wire nestled within that S. “This cable is called the pigtail,” he said, “and here at the end of the pigtail”—the laser dot jiggled on a small, rounded bead—“is the gamma source: not much bigger than a grain of rice, but it’s two hundred curies of iridium-192.” The bead looked chillingly familiar.
“How does it work?” Emert asked. “There’s a lead shutter at one end? It opens and sends a beam of gamma rays out the tube?”
“This is the strange part, to my way of thinking,” said Thornton. “To take a radiograph, you put the film behind the pipe, you hide behind a shield, and you turn a crank that pushes the pigtail out the end of the box. That lets the gamma rays from the source go through the pipe — and pretty much anything else nearby — and hit the film.”
“Seems kinda primitive,” said Emert.
“Kinda dangerous, too,” I added.
“Yes, it does,” said Thornton. “And yes, it is. Anytime somebody’s using one of these, it’s important to get everybody else out of the area. The people who use these things tend to get the highest annual radiation exposures of any workers in the nation — ten times what somebody at a nuclear power plant gets. And that’s if the thing’s working right. If something goes wrong, it can get real bad, real fast.” He showed a picture of a pigtail — just the wire cable and the bead of the source, detached from the camera. “Occasionally the pigtail comes loose,” he said. “The operator thinks he’s reeled it back into the camera, but instead, it’s lying on the ground, sending out all this gamma at anybody unlucky enough to come close.”