You're presumably thinking alpha particles if you're thinking of radiation which is stopped by, and therefore concentrates measured exposure at, your skin. I rather strongly doubt this machine uses alpha particles. Considerations which make me doubt this: they would get blocked by insulating materials such as e.g. the side of the surveillance van, the side of your vehicle, 3 cm of open air, etc.

No, X-rays have different penetrating power based on frequency. There using a back-scatter approach as it's just one van which means very low penetrating power. https://en.wikipedia.org/wiki/Backscatter_X-ray

Bananas throw out beta radiation. It's not as penetrating as alpha - attenuation depth in water on the order of centimeters rather than millimeters? - but I think a banana-equivalent dose will be pretty solidly concentrated in your digestive tract.

No, the banana is radioactive from potassium-40, which your absorbing and spreading throughout your body.

However, you also excrete potassium making the Banana equivalent meaningless as it's calculated by assuming you kept that potassium for 50 years which simply does not happen. AKA you would end up with less than 365 Banana equivalent doses by eating 1 banana a day for 1 year. (https://en.wikipedia.org/wiki/Banana_equivalent_dose)

PS: Due to homeostasis you generally get less than 1/500th Banana equivelent dose from eating a Banana.

Right, forgot about that part. Thanks.

Its mostly the fault of one isotope of potassium and many hiker types eat bananas specifically to boost their blood K levels because otherwise they get really annoying muscle cramps. Its a moderately strong beta emitter and the range in water (close to human body) is about 2 cm or so. There are probably no parts of your innards more than 2 cm from the nearest bodily fluid (blood or whatever).

Humans are surprisingly radioactive BTW. We each have about a hundred grams of potassium happily radiating away. An interesting technological challenge for a startup might be using purely passive radiation monitoring to detect humans. For security sensing or something. Maybe in a 100 years automatic supermarket style doors will sense humans radioactively rather than current microwave doppler and infrared systems. Maybe.

> An interesting technological challenge for a startup might be using purely passive radiation monitoring to detect humans.

Beta is super-easily stopped. A piece of cardboard or tinfoil reduces it dramatically, or stops it completely, depending on energy per particle, total flux, etc.

I've a Luminox watch, the dial is visible in darkness all the time, you don't have to "recharge" it. It works by having small amounts of tritium decay within luminescent tubes. The radiation produced is beta - but the levels of radiation outside the watch are essentially zero. The body of the watch is enough to contain it.

Again, and as others pointed out in other contexts here, it depends on the energy. Tritium has 20keV betas AFAIR. Some elements produce multi-MeV beta decay. That is not stopped by thin cardboard.

> beta radiation. It's not as penetrating as alpha

That's the wrong way around. Alpha radiation barely penetrates at all.

Ah, yeah, meant gamma there.

Isn't all x-ray exposure one sided based on the radiation source? Doesn't all radiation exposure start with the skin? X-ray penetrate so not all energy is deposited on the skin's surface.

Backscatter only works because the frequency does not penetrate very well.

https://en.wikipedia.org/wiki/Backscatter_X-ray

PS: Airport scanners are estimated at 1 death per 200 million scans so if used in every airport they would kill ~4 Americans a year. http://www.rita.dot.gov/bts/press_releases/bts016_13

> The radiation doses emitted by the scans are extremely small; the scans deliver an amount of radiation equivalent to 3 to 9 minutes of the radiation received through normal daily living. Furthermore, since flying itself increases exposure to ionizing radiation, the scan will contribute less than 1% of the dose a flyer will receive from exposure to cosmic rays at elevated altitudes.

http://www.ncbi.nlm.nih.gov/pubmed/21444831

Backscatter deposits that radiation disproportionately in areas of the body that are prone to cancer - skin, testes, breast tissue, etc.

So those areas that are particularly sensitive take a disproportional hit with this technology.

This [1] is a letter from a group of prominent scientists and oncologists at UCSF who wrote a letter to the White House about the uncertainties of the technology when it was used by the TSA at airports.

[1] https://www.whitehouse.gov/sites/default/files/microsites/os...

<slightly OT>

I was lucky enough to ride on the Concorde from Heathrow to JFK when I was about 12 (the 747 (seats ~400) we were supposed to take broke down, and they only had a 737 (seats ~300) and a concorde (seats 100) available; my dad, having many tens of thousands of airline miles and super double platinum status on basically every airline, including british airways, was able to get our family of four as part of the hundred that got on the concorde for that flight).

The cruising altitude of the concorde at mach ~2 is between 60 and 65k feet, basically double a normal airplane (wikipedia says 60k, but I distinctly remember the monochrome LCD in the plane that said we were traveling 1350 mph at 64k feet)

I'm curious, now, what my cosmic radiation dosage was at that altitude. Surely, given the nature of atmosphere and radiation, the dosage at twice the normal altitude is considerably more than twice what it is at 30k feet. I wonder what that did to my chances of getting a radiation induced cancer now ;)

As an aside, that happened well before 9/11, so I was actually able (/invited by the flight attendants) to go to the cockpit and talk to the pilots while were cruising along at mach 2. I remember asking the pilot what the actual takeoff speed was (he said about 175 mph, if I recall correctly. Given the glued-to-the-seat acceleration we experienced on take off, sounds about right), and all sorts of other nerdy questions about the technology.

I'm gonna pour one out for the pre 9/11 days when curious kids could visit the cockpit of an airplane and be a nerd with the pilots.

I'll pour another one out for the Concorde.

I still remember it pretty vividly (though memories can of course be deceiving ;), but we made it from heathrow to jfk in 3.5 hours. I believe, also, that with the time change, we landed about 15 minutes before we took off.

</OT>

I've now been living in NYC for ~15 years (moved here about 3 weeks before 9/11), and have watched the NYPD develop it's various anti-terrorism tactics. From the weird aluminum devices I've seen in penn station next to the armed-with-assault-rifles national guard folk on major travel days, to the stickers on the street food carts citing their affiliation with some NYPD anti-terrorism program, I've been concerned for years about the NYPD overstepping reasonable bounds on their behavior.

Where does this end? How do we encourage the police to actually be reasonable? I do have an acquaintance in the NYPD (we went to college together), but conversation on this topic is more or less not possible. The thin blue line is very much a thing, and it appears to be impenetrable for us 'civilians' (the general attitude I got from said acquaintance is "you wouldn't understand").

After reading caf's comment about Concorde's radiation detector, I came across this: "To protect passengers and crew from unnecessary radiation exposure, airworthiness authorities of Britain and France require that civilian aircraft, which fly above 50,000 ft, have a solar cosmic ray warning device. If the radiation level reachs 100 millirem/hr, the pilot is to descend to a lower altitude." - https://www.faa.gov/data_research/research/med_humanfacs/oam...

Guessing there aren't a whole lot of civilian planes affected by this rule :-D

Another benefit of the Concorde is that you were exposed to that radiation for a much shorter time than the passengers flying at 40k feet for hours longer.. I'd like to see the comparison but am too busy to do it myself tonight.

People have fairly safely spent months in outer space so your risks are probably ~1/1000th of a fairly safe level. (Record is 879 days.)