Hey Dr. Zoomie – I know we’ve never had a dirty bomb and most of what I read is about how unlikely an attack with one is. But then I hear about this guy in Florida who said he built one and seems he was going to set it off. How worried should we be?
Wow – thanks for bringing this up; I hadn’t heard about it. And what an intriguing incident, too! So let’s start with what we can tell from the photos….
One of the photos shows something I know all too well – a yellow plastic box with a radioactive materials label stuck to it and the word “Troxler” molded into the plastic – I’ve used these things in the past, been trained on them, and did a couple of consulting projects dealing with various aspects of them. Anyhow, dissecting the photos and the story, we can tell:
- Troxler is a company that makes “nuclear” gauges that are used to measure the density and sometimes the moisture content of soil (to see if it has the strength to support a building, roadway, etc.)
- Density is measured using a Cs-137 source with maybe 10 mCi of activity
- Moisture content is measured using an Am-241 source (mixed with beryllium to produce neutrons) with about 40 mCi of activity
- The amount of activity in this gauge isn’t nearly high enough to cause dangerous levels of radiation, nor to contaminate a huge area.
- Oh – and you need to have a radioactive materials license in order to legally buy and possess one of these gauges.
That’s the gauge, and then we’ve got a photo of a guy who gives off distinct homeless vibes and, when the cops who pulled him over asked about the assorted guns and stuff they found, he told them he also had a “dirty bomb” (although the story does not tell us if he had explosives in addition to the Troxler gauge, one of the charges is for “false report of a bomb or explosive,” suggesting that all he had was the gauge). Along similar lines, he was also in possession of radioactive materials, almost certainly without having an appropriate radioactive materials license…although I’m not sure that’s a criminal offense.
It does make one wonder, however, how this guy got his hands on the gauge. If Troxler was following regulatory requirements (and they’re pretty good about that) they wouldn’t sell and ship a source to a person without first seeing a copy of their radioactive materials license, nor could a licensed company sell one of these gauges to a person who lacks a license. It’s possible the gauge was stolen, although there is a regulatory requirement to secure sources and devices from unauthorized removal and theft. More likely, though, is that the source simply fell from or was bounced out of the bed of a pickup truck lurching across a construction site, which happens from time to time. A company I used to work for lost a Troxler gauge that way; it reappeared a few years later and a few states away from where it disappeared.
So – could this have been made into a “dirty bomb” by our terrorist wanna-be? I’m going to hazard a guess of probably not. But, what with all the guns, claiming to have explosives, and claiming to have what is characterized as a weapon of mass destruction, the Florida man has so many pending charges as it is, let’s not saddle him with theft as well…not without proof, anyhow.
Here’s the thing – the radioactive materials themselves are sealed inside of welded stainless steel or titanium capsules that are rated to withstand the sorts of damage that can occur on a construction site. The sources are within shields, and the shields are contained within the body of the gauge itself, which is also designed to protect the sources from the rigors of a construction site accident. So for the guy to have made a dirty bomb he’d have had to find a way to remove the radioactivity sealed inside a source buried inside the gauge…and all to be able to contaminate an area the size of, say, the lobby of a large building. All in all, no matter what the guy’s motivations and plans happened to be, it doesn’t seem as though he was in a position to make and use a dirty bomb.
Having said that, the guy sure seems as though he was up to something, what with the guns, knives, battering ram, and night vision goggles, and thermal imager for his scope. And the presence of the Troxler gauge is a big unknown but, whatever his intentions, the threat of him actually setting one off seems pretty low.
With all that, there’s one more thing I want to mention. A few of the stories I found say that the gauge “contained less radioactivity than a medical x-ray” and this sentence is just wrong. Radiation is energy that’s transferred from one place to another. This energy might be given off by unstable atoms – that’s radioactivity. But it can also be produced and given off by a machine…like an x-ray machine. Or, to put it another way – a chunk of uranium is radioactive; a Cs-137 source is radioactive, my stainless steel soap dispenser that’s contaminated with Co-60 is radioactive. For that matter, when I was injected with F-18 for a PET scan I was radioactive. But even when it’s emitting radiation, an x-ray machine is simply an incandescent light bulb that’s emitting very high-energy photons (x-rays) instead of visible light. An x-ray machine is not radioactive and it does not contain radioactivity. What I suspect the media was trying (badly) to say is that the amount of radiation one might receive from being around the gauge is less than what one would receive from an x-ray. And that is actually the case – I’ve measured Troxler gauges and I’ve measured dose from x-rays, so I can vouch for that one!
And that’s about all I can think of to say about this particular story.