Bombs or Bananas?

It seemed like a reasonable enough idea. Responding to fears of a terrorist attack by ‘dirty bomb‘ or nuclear weapon, US Customs and Border Protection installed hundreds of radiation portal monitors at seaports, land border ports of entry and crossings across the United States. But unfortunately, the devices have had trouble telling the difference between bomb-making materials and ordinary consumer products like bananas, kitty litter and toilet bowls. Worse still, they may be unable to detect a shipments which do contain bomb-making materials like highly enriched uranium.

The problem is that some of the commonest materials used in nuclear bombs — uranium-235 and plutonium-239 — don’t give off a lot of radiation. So, as Daniel Engber explains in Slate, " To suss out these materials, a detector must be set to a very high sensitivity. If the sensitivity of the screening device is high enough, then naturally occurring radioactive materials can set off a false alarm." A surprisingly large number of products contain levels of radiation capable of setting off the detectors.

In a 2007 speech Nuclear Regulatory Commission Chairman Dale E. Klein said:

Last year, I visited the Port of Seattle and toured the radiation detectors operated by U.S. Customs and Border Patrol at the Port. Their primary mission is to examine cargo entering the U.S. that may contain nuclear materials that could be used in weapons or dirty bombs. They have excellent equipment and well-trained and motivated agents. Part of that training is to understand what is a real threat versus a naturally occurring source. They need to make decisions—at this one facility, they average 1600 hits per month. In fact, while I was there one cargo container triggered the alarms. It was a shipment of Chinese fireworks and isotopic analysis showed the culprit was potassium 40.

The Customs agents told me about one particular port that receives nothing but bananas – and virtually every shipment sets off the detectors.

Mistaking bananas for bomb making materials isn’t the most serious problem. A 2006 report by the Government Accountability Office (GAO) reported the results of tests showing that the detectors frequently either missed or failed to correctly identify potentially dangerous materials. According to the report, "the incidence of false negatives among the three vendors who received contracts ranged from about 45 percent to slightly more that 80 percent."

In an article for the Scientific American, Thomas Cochran and Matthew McKinzie argued that while it might be difficult to obtain uranium, "smuggling it into the U.S. can be a straightforward matter". How do they know this?

In the summer of 2002 an ABC News unit successfully slipped a lead-lined steel pipe containing a 6.8-kilogram (15-pound) cylinder of depleted uranium (DU) past U.S. Customs and Border Protection by placing it inside a standard cargo container.

According to Cochran and McKinzie, depleted uranium can’t be used to produce a weapon but creates a radiation signature similar to highly enriched uranium. "If the source is wrapped in a one-millimeter-thick layer of lead, the radiation dose rate from HEU with no uranium 232 is less than the dose rate of similarly shielded DU." They argue that radiation portal monitors would be unable to detect a shipment of highly enriched uranium if it was shielded and packed near the centre of a shipping container.

Critics like California Congressman Henry Waxman, claim that the radiation portal monitors are just another example of the Bush administration’s waste and mismanagement.

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Lucky Alphonse
Lucky Alphonse
16 years ago

uranium 232


Don Arthur
Don Arthur
16 years ago

Lucky A – I’m not an expert on this but my understanding is that ‘232’ is the mass number. Elements like uranium can take different forms depending on the number of neutrons they have. These forms are called isotopes.

But you probably already know that already. I didn’t pay much attention in science class when I was at school so I had to look it up.

From what I’ve read, weapons grade uranium would typically be around 90% uranium-235 with some uranium-238 and uranium-234. If the uranium feedstock used in the enrichment process is contaminated with uranium from reprocessed reactor fuel then you’ll also get some uranium-232 and -236.

The presence of absence of uranium-232 matters because it’s is very radioactive. That means that it’s easier to smuggle uranium if it’s not contaminated with uranium-232 (or so I’m told).

I found this article helpful.

If anyone thinks I’m confused about this, the comments box is all yours.

Graham Bell
Graham Bell
16 years ago

Don Arthur:

Interesting and very relevant topic; one that needs to be discussed robustly here in Australia. Every time I hear someone poo-hooing the idea that the components of nuclear or radiological weapons could be smuggled into Australia – or New Zealand, for that matter – I think of that intelligence expert who, in Singapore in late 1941, said that the Imperial Japanese were nothing to worry about because their all troops were puny, short-sighted, hissed when they spoke and were equipped with shoddy out-of-date weapons. Yeah. Right.

Not impressed by that ill-behaved link though; does that mean I’ll get Christmas cards from NSA? :-)

Don Arthur
Don Arthur
16 years ago

There’s an article in this month’s Atlantic Monthly about uranium smuggling.

Lawrence Scott Sheets tells how radiation detectors in Georgia (the ex-soviet republic not the US state) foiled at least one attempt at smuggling:

Dadayan made only feeble efforts to conceal his stash of HEU, hiding it in a cellophane bag tucked inside a metal tea box. But several specialists I spoke to speculated that because his HEU, according to U.S. analyses, also contained the chemical compounds UO2 and U3O8 (which emit more radiation than U-235), it set off the radiation detectors the Georgians had at the border. The guards say that when the sensors sounded, Dadayan tossed the satchel containing the tea box filled with bomb-grade uranium onto the ground. He said hed never seen the substance in the box before and that the cellophane bag had only been for food scraps. So sloppy were his smuggling efforts that, according to Armenian court records, his notebook contained scribblings mentioning U308 and the amount of moneybelieved by Georgian officials to be $15,000that he was to receive for acting as a nuclear mule. Dadayan was handed over to the Armenian government, tried, and sentenced in 2004 to two and a half years in prison.