Andy Karam, Homeland Security Scientific Advisor, Mirion Technologies, USA
In the Spring of 2014, the NYC Department of Sanitation (DSNY) was cleaning out a vacant lot in the Borough of Queens when they found a metal cylinder that was about 25 cm in diameter and about 40 cm long that weighed about 30 kg. It had a cavity in one end, and the word “Uranium” was stamped in the metal on one side. There were also some projections at the top that could be used to carry the cylinder.
As DSNY inspected the site further, they found other items that appeared to be plastic buckets, medical tubing and needles of some sort – three or four sets in all – but these seemed to have nothing to do with the metal cylinder.
What instruments told us
Since the Department of Sanitation finds radioactive materials in the trash fairly frequently (usually radium watch dials, radioactive rocks, or medical radioactivity) they are proficient in the use of radio-isotope identifiers (RIIDs) so they brought their instrument to the site and were surprised that the cylinder was identified as being highly enriched uranium (HEU). Radiation measurements obtained on contact with the cylinder indicated a dose rate of about 10 µSv/hr – about 20 times as high as normal background radiation dose rates in that part of New York. At this point, DSNY contacted the NYPD and asked for assistance with identifying and resolving the matter.
Investigating and resolving the matter
When I arrived at the scene with the NYPD Counterterrorism Division, I confirmed the DSNY radiation dose rate and nuclide identification. At the same time, it seemed unlikely that a nuclear weapon had appeared in a vacant lot in Queens. In particular, the shape of the object was wrong, and to the best of my knowledge, we do not stamp “Uranium” into the actual fuel for such devices. However, the cylinder was the shape of a depleted uranium (DU) shield frequently used for medical radioactivity, and the tubing and bucket that were found were consistent with a device used to produce Tc-99m for medical use. On the other hand, the nuclide identifications that I was obtaining with the RIID simply did not make any sense – it insisted that the metal was weapons-grade uranium and that the tubing contained an isotope of cesium (specifically Cs-134, which is produced in nuclear reactors in relatively small quantities).
When I took a closer look at the cylinder itself, I noticed the name of an American radiopharmaceutical company and a serial number stamped into the metal. One of the detectives demonstrated his investigative talents by locating the company’s radiation safety officer and placing a call, then turned the phone over to me. When I read the serial number the RSO replied “Yep – that’s one of ours. We lost 8 of those from a customer on Long Island about 6 months ago and we were wondering what had happened to them.”
I decided not to reply with what first occurred to me to say and, instead, simply thanked him for this information and informed him that his company would, of course, be responsible for shipping the cylinder and other materials back to his facility, which he agreed to do. With that out of the way, we realized that we still had another 2-3 sets of tubing, plastic buckets, and other internal materials – but we had no corresponding DU shields. So we spent the next hour or so searching the vacant lot and surrounding areas to see if those would turn up. Unfortunately, we were never able to find any additional shields.
How radiopharmaceutical generators work
One of the most commonly used radiopharmaceuticals is Tc-99m – a radionuclide with a half-life of only about 6 hours. Tc-99m is produced from the radioactive decay of its parent, Mo-99; this is, in turn, produced from the fission of U-235 (the uranium isotope used to make nuclear weapons and reactor fuel). Although Tc-99m has a very short half-life, the Mo-99 parent, with a half-life ten times as long, will last long enough to ship anywhere in the world and to serve as a source of Tc-99m for at least 3-4 weeks. So the Mo-99 will be produced at a reactor facility, the Mo-99 is chemically separated from the rest of the radioactive material, and it is adsorbed onto an ion exchange column similar to the one shown here. This, in turn, is placed inside the DU shield, connected to the various tubes, and shipped to the final user.
When the Mo-99 decays, it forms Tc-99m. At the nuclear pharmacy, the Tc-99m (which is a different chemical element from Mo-99) can be removed from the ion exchange column by injecting saline solution into the tubing – the amount of radioactivity in the liquid is adjusted to what the pharmacist ordered and is injected into the patient. When enough time has passed (usually 3-4 weeks) that the Mo-99 is exhausted and no longer producing Tc-99m, the generator is exchanged for a new one and is returned to the vendor. This is usually done by a courier company – in this particular case, the courier seems to have made a number of mistakes that culminated in all of this ending up in a vacant lot in Queens.
Final Disposition
Once we got all of this sorted out, we still needed to find a place to store the DU shield until it could be returned to the radiopharmacy. So I called a friend and colleague of mine who was in charge of radiation safety at a Manhattan hospital. He agreed to store all of this temporarily, until the vendor could arrange for its return. So my friendly detective called the NYPD Highway Bureau to arrange for an escort into Manhattan. In all honesty, I felt that this was a bit excessive – depleted uranium just is not very radioactive. But the detective insisted he had already placed the call, and our escort showed up about a half hour later.
I have to admit that the ride into Manhattan was exhilarating, if not necessarily warranted. It was close to rush hour and the highways were already filling up. But the motorcycles, lights and sirens going, cleared a path for our black SUV (which also had its lights and sirens turned on), and the detective was enjoying himself greatly, so I just did not want to interfere with his fun. And at speeds from 100-150 km/hr, we made the trip much more quickly than is normal at rush hour! We pulled into the hospital and transferred the DU shield and assorted tubing to my friend, then returned to our command. Oh – and interestingly, the vehicle we transported the cylinder in also happened to have four very large radiation detectors inside (this vehicle was also used for our radioactive materials interdiction missions). With some huge detectors and plenty of time (while we zipped across New York), the cylinder was finally correctly identified as depleted uranium!
Once back at the office, I also had some work to do. First was to notify our regulators (city and state) about what we had found; they, in turn, notified the Federal government, who had some pointed questions for the radiopharmacy. I also had to report on this event to my chain of command – both uniformed and civilian. We also had to find out if this was a widespread problem or a one-off event. And, lastly, we needed to notify other jurisdictions in our area what had happened so that they would know to be on the lookout for DU cylinders and how to respond if they were found.
Why DU was identified as HEU
Finally, we have the question as to how depleted uranium could be mis-identified as highly enriched uranium since these are so very different. I have to admit that I am still not exactly certain about this, but here is my best guess.
As DU decays, it goes through a whole series of radionuclides before it finally ends up as stable lead (Pb-206, to be precise). One of these intermediate nuclides is radium – Ra-226 – and this radionuclide has a “fingerprint” that is very close to that of U-235 (the uranium isotope that blows up nicely). It is very difficult for the type of RIID that we were using to tell the difference between U-235 and Ra-226 since their “fingerprints” are so very close together. So I suspect that the RIID, seeing the Ra-226 as well as the U-238 (which is what DU is) thought that it was seeing U-235 plus a little DU, and mis-identified the whole thing as a nuclear weapon. That is just a guess, but it makes sense, given the type of detector we were using. In any event, a larger and smarter detector was able to (finally) understand what was going on!
About the Author
Andrew Karam has over 35 years of experience in radiation safety and nuclear power, beginning with his time in the US Navy. For the last 10 years he has been working on issues related to radiological and nuclear emergency response and counterterrorism, including several years as a scientist with the New York City Police Department. He currently works for Mirion Technologies as a Homeland Security Scientific Advisor.
