Equipment Focus: Radiation Detectors

Radiation detectors are a necessity for scrap processors and consumers. This review examines the state of this technology and how to get the best results from your system.

By Jim Fowler

A few years ago, when the U.S. steel and scrap markets were suffering, some manufacturers of radiation detection equipment wondered if they should be looking for something different to do—their business was awful. Most of the mills and major scrap processors had systems, no radioactive sources had caused serious incidents, and discretionary funds weren’t available to either expand or upgrade existing radiation detection systems. 
   Then a series of unrelated events changed those bad times for detector manufacturers.
   First, there was dramatic improvement in the demand for steel and scrap. Next, some undetected radioactive sources resulted in expensive mill cleanups. These factors led to a sharp increase in the demand for detection equipment—principally new systems with improved technology to replace older, less-effective units. The stronger business conditions enabled scrap consumers to make the investment to protect themselves even more from radioactive contamination.
   Consumers also insisted that their scrap suppliers upgrade their equipment in “a lockstep movement of the steel and scrap industries to be radiation-free,” as one detector producer puts it.
   Beyond the scrap industry, 9/11 prompted the United States to increase protection of military installations, nuclear power plants, and ports from unauthorized entry of radioactive sources. One way to do that was to install radiation detection equipment. For detector vendors, the drought was over.
   Today, gate or portal monitors are an essential part of homeland and industrial security, with the number of installations growing daily. Though the steel and scrap industries are a fraction of the overall market for radiation detection equipment—now dominated by security demands and ports in particular—manufacturers haven’t forgotten their beginnings. They view the steel and scrap industries as an attractive replacement market for upgraded and expanded equipment. 
   Manufacturers interviewed for this article estimate that 75 to 80 percent of U.S. scrap processors have radiation detection equipment. Of that group, about 80 percent have gate monitors and handheld units, while the other 20 percent have only handhelds.
   The 20 to 25 percent who have no detection equipment are living dangerously, manufacturers assert. If you’re the only scrap dealer in town without a detector, they note, you’re vulnerable to suppliers seeking to get rid of a radioactive source by burying it in a load of scrap.
   That’s why detector vendors assert that even the smallest scrap operation should have at least a handheld radiation detector.

Technological Transformations
Gate or portal radiation detectors are by far the most popular units in the scrap industry. The industry standard for size is probably 4,000 cubic inches of detector material to securely scan a truckload of dense scrap, says a manufacturer, though some systems are as large as 20,000 cubic inches. The cost of these units can range from $18,000 to $90,000. For a mill installation, the numbers can go even higher.
   “It all depends on the level of confidence you want,” says one detector expert.
While early systems used sodium iodide (a fragile, organic crystal that is grown and considered more sensitive and more expensive), newer units are the large, manmade plastic scintillators. These units feature polyvinyl toluene (PVT), which looks like Plexiglas. This detection material has the advantages of not being immediately affected by exposure to the elements, plus it can be shaped to a desired size.
   “It’s durable, reliable, and can take the wear-and-tear associated with a scrapyard or steel mill,” a vendor notes.
When radiation hits a plastic scintillator, a material in the PVT excites the electrons. After being excited, the electrons return to their normal state, giving off the excess energy as light. This light is transferred through the PVT into a photo multiplier tube (pmt). The system’s computer monitors the information it receives from the pmt, signaling an alarm when the counts exceed a specified level.
   While the life of PVT depends on its environment, one detector maker says it eventually develops cracks and gets cloudy, losing its transparency and its ability to transmit light to the pmt.
   “It’s a slow degradation process,” he says, “but they do have a finite life” —about eight to 10 years, on average, though the development of a new PVT formula is expected to extend the product’s life. 
   How do you know if your PVT system is wearing out? Do a daily operational check, with one manufacturer recommending a check in the morning before you begin operations and a check at the end of the workday.
How you accomplish this check depends on your detection system. Some systems require you to use a small quantity of radioactive material that you expose to the detector at a given geometry.
   For example, let’s say you always hold the radioactive test source X number of feet from the unit’s detector to make the alarm sound. If the alarm doesn’t sound at X feet—if you have to move the source closer to the detector to make the alarm go off—then there is obvious degradation in the system. That doesn’t necessarily mean the detector is failing. The problem could be a circuitboard or in the cables since electronics are a key part of modern radiation detection systems.
   One major innovation, says one manufacturer, has been an internal test source. The operator simply pushes a button on the console to test the system, eliminating the need for an external test source.
   Another innovation has been the greater sensitivity of modern detection systems. While big radioactive sources are easy to detect, the problem has always been detecting low-level sources. To address this problem, manufacturers ratcheted up the sensitivity of their systems to detect such weak sources.
   “With high-speed computers, advanced algorithms, larger detectors, and more pmts, detectors are at least 80 percent more sensitive than they were 10 years ago, and probably more,” states one vendor.
   Greater sensitivity, however, created another problem—frequent false alarms.
   “Previously,” a vendor explains, “sensitivity was the entire name of the game. In the last three or four years, we’ve reached a point where sensitivity is approaching the maximum end. With that achievement, you also have to make a system that doesn’t cause people a lot of grief by giving them false alarms.”
   Manufacturers examined what was causing the problem so their software and electronics could recognize a false positive before the alarm went off. Their testing showed that the false positives could be traced to several issues related to detection sensitivity. They found that voids in the load, load density, and load characteristics—such as whether it was in a truck or a railcar—would change the number of counts per second their detectors received. They then developed a number of mathematical algorithms that would differentiate the load characteristics, thus reducing the number of false positives.
   “This is where computers come in handy—to determine what the count increases really represent,” one detection expert notes. “At first we used some pretty simple electronics, then microprocessors, and now we’re using powerful computers that can quickly analyze these graphs to determine more accurately if the spike is caused by a pocket or a radioactive source.” One manufacturer claims that false positives are down to one per 1,000 loads inspected.
   As another explains, “the detectors and the science behind radiation measurement haven’t changed in 15 years. It’s the electronics, the algorithms, interfaces, software codes—all the new technology used for consumer electronics and computers—that are being integrated into the system’s console. As a result, the systems are more robust, more sophisticated, and able to crunch and process data and scientific algorithms in microseconds. Our instruments will follow the advances in electronics.”
   Another detector maker concurs, noting that what has changed is the application of digital signal processors, electronics, and computer software.
   “We test our detectors to see just how small a source we can detect,” he says. “Through this testing, we’ve developed very sophisticated mathematical algorithms that allow us to have high sensitivity levels and fewer false positives. So, even though the detectors haven’t changed, everything associated with the electronics has changed to the point where we have much more sensitive units today.”
   Today’s detection technology also enables users to choose what they see when a load of material passes through the detector. In short, the information that appears on the system’s computer screen can be as simple or as complicated as the customer wants, says one vendor.
   The monitor, for instance, can have a green light (pass) and red light (fail), or it can have a screen that tells the operator that the offending material is four feet back in the load, on the right-hand side of the truck, and is X counts above background, he notes.
   The configuration of your system becomes a function of your requirements as well as price. If you’re a large scrap processor and you’re pushing through a lot of trucks and/or railcars, you’ll probably want high sensitivity levels, which means a more sophisticated system. “This issue is not just simplicity,” the vendor says, “it’s how sensitive your system needs to be in order to detect low-level radioactive sources.”
   Aside from gate or portal detection systems, portable, handheld detectors are critical for every yard because they allow processors to sweep material once it is in smaller piles, when radioactive sources become more obvious.
   One manufacturer reports that a growing trend is for scrap processors to take a portable unit to do a preliminary scan of material they plan to buy. “They want to check it out before they get it into their yards,” he explains.
   Handheld detectors are made with either sodium iodide or geiger tubes, with sodium iodide units being more sensitive and more expensive. These detectors can range in price from $800 to $10,000, so take a close look at what you need to accomplish.

Points to Ponder  
To figure out what’s best for your processing operation, you need to consider several issues.
   The first is to find out what detection levels are required by your consumers—that is, how sensitive are their own detection units set? “A scrap dealer is going to have to at least match those levels,” one detector maker states.
   You should also describe the types of trucks and/or railcars that enter your plant as well as the grades of scrap you handle. This information will help the vendor recommend the right system for your operation.
The number of bells and whistles you want will also have a bearing on the system’s cost. For example, do you want a touchscreen? A printer? A modem so the manufacturer can check your system remotely if you have a problem?
   Service is certainly one issue you’ll want to discuss with manufacturers as well as scrap dealers using their systems. One vendor boasts that by using a phone modem, a customer can have a detector problem analyzed almost immediately without having to wait for a service representative. He adds that when his company upgrades the software for its detectors, it will be able to provide system updates to customers, by modem, without charge.
   In short, you need to “look and learn before you buy,” says one vendor. Talk with other processors as well as consumers to see what equipment they’re using. Request technical information from various manufacturers. You can also check with NASCO-OP—the purchasing cooperative for the scrap industry—about potential deals on detection products. (NASCO-OP can be reached at 800/321-3396 or www.nascoop.com.)

Detecting Trouble
As for how to get the best results from your detection system, don’t forget that trucks or railcars must pass by the detector at a slow enough speed so the detector can do its job.
   “A load of scrap flying through a monitor makes it difficult for detectors to spot a radioactive source,” states one detection expert. “Controlling the speed of trucks and railcars passing through gate monitors is critical, and this has been a huge industry change.” Today, this expert notes, processors and consumers are more conscientious about monitoring the speed of trucks and railcars, something that “wasn’t happening five years ago.”
   Even at the correct speed, it’s possible for a low-level radioactive source to slip by virtually any detector. That’s why it’s prudent to monitor not only inbound loads but also outbound shipments. As one vendor explains, “a load could contain slightly contaminated material that doesn’t set off the alarm. If that material is somehow grouped together in an outbound load, collectively it could produce enough counts that it’s picked up by the detector. It can happen.”
   Some processors even have radiation detectors at their processing machinery—such as on the infeed conveyor to a shredder—to prevent previously undetected sources from being processed.
   There are also radiation detectors mounted to the base plate of a grapple and installed on the boom of hydraulic material handlers. “You want to be able to protect your processing equipment from contamination and be sure that the material you’re shipping out is radiation-free,” a manufacturer says.
   One vendor claims to have successfully installed radiation detectors in lifting magnets, something that others say is impossible because of the heat generated by such magnets. Because of the claims and counterclaims associated with grapple and magnet detectors, you should consult manufacturers as well as processors who are using this equipment.
Looking to the future, one manufacturer believes that “industry pressure—from scrap consumers and larger processors—will cause more and more smaller yards that don’t have detection systems to add them.” He also sees the larger yards continually upgrading their systems to stay in sync with their consumers. 

The Radiation Detectors
ANTECH Corp., 303/430-8184, www.antech-inc.com 

Berkeley Nucleonics Corp. , 800/234-7858, www.berkeleynucleonics.com 

Exploranium G.S. Ltd. , 905/670-7071, www.exploranium.com 

Ludlum Measurements Inc. , 325/235-5494, www.ludlums.com 

Rad/Comm Systems Corp., 905/678-6503, www.radcommsystems.com 

Thermo Electron Corp. , 505/428-3534, www.thermo.com/rmp 

Veridt L.L.C. , 608/833-1823, www.veridt.com

Jim Fowler is retired publisher and editorial director of Scrap.