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Comment by mrbill | Hacker News Reader

A lot of smoke detectors use the radioactive isotope americium-241 in an ionization process to detect smoke. Get enough smoke detectors, and you can have a good amount of radioactive material.

Read up on David Hahn, who hit the news in '94 for trying to build a breeder reactor in his back yard using sources scavenged from among other things, smoke detectors.

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A smoke detector contains about 0.25 μg of americium [0], which is painted on the inside of a chamber. In small quantities, it seems americium dioxide can only be dangerous if inhaled [0].

According to David Hahn's Wikipedia page[1], his reactor used thorium, purified from thorium ash used in lantern mantles, and not americium.

What's more, smoke detectors go straight to landfills in many places. I think it's unresonable to consider them a realistic threat.

[0] http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf

[1] http://en.wikipedia.org/wiki/David_Hahn#Creation_of_the_reac...

He was arrested again in 2007 for collecting smoke detectors to collect americium.

Sounds unlikely, as he seems intelligent enough to know he'd need (at least) millions of smoke detectors.

Thank you. It's depressing how quick people can be to dismiss something as stupid without considering how those rules came about in the first place.

And so what? some guy stabs someone with a screwdriver and the US regulate the export of them between Commonwealth countries, still without regulating the AK-47 in its own country? There is more regulation on CNC machining center than on firearms. It's stupid. The US doesn't refrain from sending hellfires missiles on weddings, which kills more surely than the once in a lifetime freak who assemble some mildly radioactive stuff in his backyard. If it's for the radiations, I see people playing with X-ray on youtube everywhere, there is 0% chance of chain reaction, nobody cares about chemical contamination in the US, so I don't know why they would freak about a mildly radioactive contamination in a foreign country either.

What I begin to see, is an entire world under occupation.

That's because an AK-47 is an AK-47: it's not a game-changer. But a CNC machining system that lets you build silent ship propellers can dramatically change the threats the world faces.

All the advances in CNC machining systems are published on the internet. And there is some degree of self replicating capability in them (basically you can machine the parts yourself, and fine-tune the design by hand to get a machine of better capability than the previous one).

> But a CNC machining system that lets you build silent ship propellers can dramatically change the threats the world faces.

Bullshit. (and yes I know about the Toshiba incident)

I didn't know about it, so I had to look it up

http://en.wikipedia.org/wiki/Toshiba-Kongsberg_scandal

Thank you for elevating our level of discourse a bit :-)

Building a CNC machine with a regular lathe and mill may not be hobbyist level easy, but it's certainly doable by someone as rich in machining tradition as Russia.

Amusingly, the incident would also dispell the (western) myth that it takes very advanced machining technology to build a nuclear bomb. You can't have it both ways.

I suspect the real incident was the software to mill those propellers, but that wasn't on the list of illegal goods. It's one thing to have a fancy but dumb CNC machine, another to come up with a silent prop design.

Incidentally, automatic rifles such as AK-47s are heavily regulated in the US. It's possible to get them, but it requires a lot of paperwork, they're all at least 25 years old, and more cannot be imported.

The More You Know.

they make some in maker fairs in garages in California.

one guy, one time, managed to get his hands on enough smoke detectors to make himself glow in the dark.. yes, seems perfectly reasonable to freak out about.

I do not know what you are referencing, but in general radiation doesn't make you glow.

He's talking about the radioactive boy scout.

Also he was talking in hyperbole.

Whoa - I actually had no idea. I always assumed it was general electronics because I was instructed to do that for every transaction - even when I was just reselling a bunch of resistors.

Yep. A quick summary:

http://www.damninteresting.com/smoke-detectors-and-a-radioac...

Apparently the risk is that someone would use it to create a dirty bomb. It's not dangerous unless ingested or inhaled, and it's not apparently easy to use as any kind of nuclear fuel. I guess this is kinda reasonable.

Radioactive smoke detectors mandatory in houses. Hmm, what's wrong with this picture?

The irrational fear that's thrown around whenever the word 'radiation' is used?

are you talking about the classification of smoke detectors as weapon material?

So much this. It's as bad as when someone is trying to demonize some chemical in food, and lists all the other things it's used in, as if that has any relevance to it's safety...

It's a pretty small amount of radioactive material, about 1 μCi (roughly equal to 2000 bananas). And in normal usage, you probably shouldn't be removing the insides of the smoke detector and eating it or anything, unlike the tasty bananas.

Nonetheless, they're being phased out in a lot of places, mostly due to disposal worries. While one smoke detector is fairly harmless, tens of thousands being dumped in landfills is more of a concern, and properly recycling them is expensive. Optical smoke detectors based on LEDs are now fairly affordable, don't have the disposal issues, and may also perform better.

And the alpha radiation emitted is barely able to penetrate a sheet of paper, let alone the detector housing and ten feet of air to your body.

But then it gets into the water supply and is bombaring your cells from nanometers away . . .

Except that americium dioxide is insoluble[0], so it wouldn't dissolve in the water supply. Even if consumed, it would pass straight through your digestive system and wouldn't accumulate in the body.

[0] http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf

Nothing, because the smoke detector uses an alpha emitter, and alpha radiation is blocked by practically everything, including a sheet of paper, or roughly 4 cm or air.

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