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This one probably has some cross-over with Skeptics SE, but I thought it fits here a little better.

The concept comes from the TV show NCIS:LA second season episode "Empty Quiver"

Here, the villains steal some nuclear material from a hospital's radiology department (in itself dubious). Then in order to transport it across the country without detection, they surround it in a truck full of bananas, as if it's nothing more than a produce delivery to a grocery store.

Ok, so let's accept that bananas contain potassium, that there exists an isotope of potassium that is radioactive and found normally in nature (including bananas) and other things as indicated here.

Is this collectively, i.e. an entire truck load, enough to fool a trained inspector?

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So your question is whether the decay of potassium-40 bananas can mask the radiation from nuclear material typically found in radiology departments? – dj_mummy Sep 20 '13 at 12:30
@dj_mummy While that was the story line of the episode, I'd like to hear a more general explanation (positive or negative) of whether bananas can disguise any material that could be used to build a "dirty nuke." – cobaltduck Sep 20 '13 at 13:10
In the past the NCIS shows have been one of my guilty pleasures, but come on. Do you really think you should take any entertainment produced for mass consumption at all seriously when it comes to how sciencey stuff works? The LA spin-off is worse than the original that way. There are many foods with higher K-40 levels than bananas. Places the idea fails: energy of the lines; geometry of the source; and a whole truckload of banana is not a strong source---NRC and OSHA would freak out if it was. – dmckee Sep 20 '13 at 14:44
@dmckee Agree! It happens too often that I try to to enjoy some movie or TV show, and some event has me mumbling "Oh, bull$&!+." and ruins my 'suspension of disbelief.' I suspected it was unlikely, but this one left me scratcing my head. I guess I hadn't made the mental leap between this quote from the link in my question: "the radioactivity from a truckload of bananas is capable of causing a false alarm when passed through ... " and the much stronger statement "if said truck contained a Goiania-like device, the authorities would just assume it was due to the bananas and wave it through." – cobaltduck Sep 23 '13 at 16:34
up vote 6 down vote accepted

This doesn't seem likely for several reasons. Most hospital waste is considered low level waste (LLW) and not very hazardous and would make for a anticlimactic dirty bomb. In fact LLW is usually just incinerated or buried with only minimum precaution. Let's assume they got a hold of something that was not LLW waste and was a high level waste (HLW) item, like in Goiania.

Something that would actually work in dirty bomb would have to be stored in a shielded container, thus you wouldn't need bananas anyway as bananas radiate very little in comparison to almost everything else (see below). But if the crooks were as ignorant about radiation as the scrap metal recyclers in Goiania who spread the glowing powder and dust around and even let a kid rub it on her skin for effect, then perhaps they took it out of the container to transport it.

At this point the exposure levels would be so high that bananas wouldn't even compare. So other than providing a snack in between bouts of vomiting from radiation sickness I don't see what bananas would do to mask it. Banana radiation does make a nice little plot trivia that helps the story seem more realistic.

Let's compare some numbers in banana terms (BED banana equivalent dose):

80 million BED = Fatal dose even with treatment

20 million BED = Severe radiation poisoning, fatal in some cases

500,000 BED = Maximum legal yearly dose for a US radiation worker

40,000 BED = Ten years of normal background dose, 85% of which is from natural sources

4000 BED = 1 Mammogram

1000 BED = Approximate total dose received at Fukushima Town Hall in two weeks following accident

400 BED = 1 Flight from London to New York

300 BED = Yearly release target for a nuclear power plant

200 BED = Chest X-ray

50 BED = Dental X-ray

1 BED = Eating a banana ( 0.1 μSv = 0.0001 mSv dosage)

That's a lot of bananas to get close to a dosage that would be fatal, so it would take a lot to cover up an unshielded radiation source. In fact our bodies carry around more BED doses than a banana.

We surrounded by naturally-radioactive materials, and are constantly bathed in radiation originating in the rocks and soil, building materials, the sky (space), food and one another. A typical background level of exposure is 2-3 millisieverts per year (mSv/y) or 20000 to 30000 BED / year.

Bananas probably wouldn't provide a lot of cover. After all don't they scan a lot of organic products and know how much to expect? So anything additional would be suspect and HLW would stand out unless it was so well shielded that there would be no point for bananas anyway.

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It's not entirely impossible, but very unlikely IMO. There's not enough information to know.

First, what type of inspection were they were trying to evade? For example, if someone drives a small truck from the east coast of the USA to the west coast, they normally would not be inspected at all. For those who have not been to the USA: There are not routine inspection of vehicles at USA state borders, like there are at many national borders. You just drive right through from one state to the next, all the way across the country.

OK, let's assume that for some reason somebody is checking the radioactivity of all passing trucks. (Maybe the FBI has been tipped that a dirty bomb will be on a certain highway?) There are ridiculously sophistocated nuclei-detection systems out there that would have no problem finding a weird isotope in a truck of bananas. But maybe the FBI doesn't have such fancy equipment, or can't transport it to the inspection stop very fast, so you just have inspectors holding off-the-shelf geiger counters near and inside the truck. I guess it could happen, why not?

Different radioactive isotopes decay in different ways (e.g. alpha, beta, gamma radiation). We don't know what they stole from the hospital. If it was an alpha or beta emitter, the radiation can be blocked by a thin shield, like a suitcase, so the bananas would be pointless. Maybe they have a gamma emitter? But bananas are beta emitters, so the sides of the truck would block the banana radiation but not the gamma. If the inspector saw a signal outside the truck of bananas, it would prove that there was something besides bananas inside the truck. On the other hand, maybe the inspectors are not very well trained! They could reach the wrong conclusion.

So if there was an inspection, and the inspectors had bad equipment and bad training, the bananas could be helpful in confusing the inspectors. But in most plausible circumstances, filling the truck with anything else would be equally effective as filling it with bananas. (That said, there's nothing wrong with bananas, and you can grab one for a nice snack during the long journey!)

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would there be any danger eating the the banana if it was in very close proximity to the gamma emitter for the duration of the trip from e.g. NY to SF? – horatio Sep 20 '13 at 15:23
Gamma radiation can do nothing to a nearby banana except make it slightly warmer and kill mold or pests, as far as I know. It's possible in principle (although I doubt it's likely) that a medical isotope could emit tons of neutrons, in which case nearby objects could become more radioactive (this is called neutron transmutation). – Steve B Sep 20 '13 at 16:15

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