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Sat, Aug. 18th, 2007, 05:19 pm
Nuclear Power

I've been reading the book Nature's Building Blocks, which I highly recommend, and a few things have stood out thus far. One of the more notable ones is the discussion of nuclear physics. Related to that, I have a few questions for anyone who might know the answer.

How come with all the journalist fearmongering about 'dirty bombs' they never mention simply dropping off radium-beryllium neutron sources in populated areas? For those who don't know, radium releases alpha particles, which when they hit beryllium causes it to release a neutron. Some shielding could easily prevent such objects from giving off conventional radiation, and sources of large quantities of nearly undetectable nasty radiation would obviously be a Bad Thing. It could be that neutrons so produced move too slow to get very far, especially since the beryllium itself slows them down, although some tradeoffs could be made there by having specks of radium in small quantities of beryllium instead of a block of radium in a block of beryllium. The materials might also be prohibitively expensive, although that appears to not be the case, or the yield in terms of number of neutrons might be low. If anyone has any real information I'd be curious to hear it.

Relatedly, would a parallelogram-shaped lens of beryllium be effective at getting neutrons from a source at the focus to all go in the same direction, or do neutrons get bounced in random directions whenever they hit a beryllium atom?

A bit more seriously (I never ask any question about why the nearly nonexistent terrorist menace doesn't do something seriously) what's wrong with using radium-beryllium (or polonium-beryllium) neutron sources as a way of getting lithium deuteride to give off lots of heat? If you embedded lots of little neutron sources in a block of lithium deuteride, there would be chained reactions giving off neutrons, without criticality because each reaction absorbs one neutron and gives off another, but if it's a big enough block those chains get long and the amount of heat could be substantial because it's all fusion. Such a block would make a great heat source to be used in the same way as the heat sources in standard nuclear reactors are used.

Speaking of which, can someone explain to me why thermoelectic generators (also described in Nature's Building Blocks) aren't standard? They have obvious reliability advantages, and their simplicity is appealing. I assume that either their efficiency or cost of materials is bad?
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(Deleted comment)

Mon, Aug. 20th, 2007 11:38 pm (UTC)

I am guessing that by "leaky crack" he meant diarrhea.

Sat, Sep. 8th, 2007 11:29 pm (UTC)

I'm thinking she had female-issues with her other crack; thus the implication of impaired fertility...

Sun, Aug. 19th, 2007 08:41 am (UTC)

Radium is 'hard to come by' in the sense that you can't buy it at your local corner store any more, but it's still well within reach of a podunk small country's resources to generate a whole bunch of it. From the descriptions it sounds like a polonium-beryllium neutron source is a force to be reckoned with, but non-nuclear powers don't have any reasonable way of getting their hands on some polonium.

My question about lenses was really whether when a neutron gets reflected by some beryllium, does the beryllium act like a sheet or a large collection of marbles? It isn't obvious to me whether the neutron should interact with the surface as a whole or just whichever atom it happens to bump into.

I can believe that the yield would basically be low. From descriptions of nuclear weapons design, it sounds like anything you could possibly come up with in terms of basic nuclear engineering was already considered in the 1950s, and presumably anything which makes decent yield has already long since been considered both for weaponry and electricity generation. It also appears that neutron bomb programs were abandoned not due to high-minded protests but simply because there are explosives which get you a lot more bang for the buck.

It's really annoying how much people fear nuclear power. If you just speak to the general public about it, you'll get the impression that three mile island had serious local environmental problems, when in fact the whole thing was contained within the reactor. It might help if people started to call the first retaining wall the 'fuse wall', since that's what the damn thing is. Even fission reactions are largely self-containing - if the interior wall melts and the reagents get spread around, they become sub-critical and the problems simply stop.

Some available thermoelectric generators are claiming efficiencies of 20%, which is very impressive, but not as good as the astounding 50%+ values.
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Sun, Aug. 19th, 2007 08:24 am (UTC)

Yeah, once in a while reality creeps in. Even the media in the US called foul with the massive fuck-up which was the hurricane Katrina rescue operation. They still haven't called foul on the 1+1=3 supply-side accounting though, so it's a bit of a stretch to say they live on planet reality.

Sun, Aug. 19th, 2007 07:05 pm (UTC)

Back in high school, I had a physics teacher that told every class of students his premise for an action movie. It centered around a terrorist plot to set off a nuclear bomb in some populated area. The intrigue/plot would be based around the way the nuclear fuel material would get from its source to the destination:

Let the critical mass of the fuel be M, and let the mass of a marginally detectable amount of the fuel be N. Now, hire/recruit P+M/N (for some P>0) participants to each bring N units of fuel to the bomb site.

The action would unfold as the FBI or CIA attempt to track down as many of the fuel transports as possible (the middle of the movie centers around catching P of them) and eventually end with a big chase to get the P+1st.

Fri, Aug. 24th, 2007 12:25 am (UTC)

This is a good example of how error correcting codes are a very bad idea when you have a very high loss rate. one-of-two or one-of-three turns out to be the way to go.

Fri, Aug. 24th, 2007 01:17 am (UTC)

Man... messed up the symbol switching there. Shoulda proofread a bit better.

That should have been, "big chase to get the M/N+1st".

Mon, Aug. 20th, 2007 10:30 pm (UTC)
booger_dawson: Spooky

It's pretty spooky to think about the Terrorist stuff. I think they don't dabble into some of it because they may be more into other things. But in time they might. I am surprised every time special forces in Afghanistan raid suspected terrorists homes and find blue prints of airports and other landmarks in the USA. When they check out the computers they have tons of information on how to bypass airport detectors and information on cyberterrorism and attacks. Such as research on how to take down power as well as many other things.

Although media shows footage that would resemble a poor country. They are highly educated than we may think. Things that scare me is Binary when I say Binary im not talking about 0 and 1 i'm talking about a mixture of chemicals that creates binary. One drop can in the words of Chris Rock "Blow Up like the motherfuc*ing God Father"

We could experience Nuclear attacks like you were mentioning, but it may come from a cult or heavily religious individuals like in Tokyo the "sarin" attack. Be careful what to believe in my friends. Sometimes it just better to believe in your Loved ones instead of other things. Believing in something can be the most lethal thing.
- Booger

Bram whats up man? Haven't seen a blog from you in a while. Had my comment post on the poker article hanging for a while. My comment made me look like a Douche... haha jk Take care man! :-)

Fri, Aug. 24th, 2007 12:26 am (UTC)
bramcohen: Re: Spooky

I'm really not interested in bullshit speculation about the capabilities and psychology behind 'terrorists'. There are practically no such people in the united states, and media commentary on them is pure fearmongering.

Tue, Aug. 21st, 2007 02:50 am (UTC)

Something like what you describe is not useful as a terror device-
A terror device needs to create an immediate threat and the constant threat of a restrike-
Low-level neutron radiation would be too scattered and take too long-
Wind-spread plutonium is about as bad as it gets here-

Fri, Aug. 24th, 2007 12:28 am (UTC)

Wind-spread plutonium would not make a particularly effective poison as compared to nerve gas, especially on a price scale.

As for what is the most effective form of terrorism psychologically, it's mostly about media attention, and the US media is quite insistent on giving lots of attention to the current terrorist activity in the US which is, quite simply, a fiction.

Tue, Aug. 21st, 2007 08:40 pm (UTC)

I had a suggestion for a bittorrent/tracker feature. I've noticed a couple of trackers are including hashes for files within the torrents. It would be good to allow the client to search by hash. IE: I have a torrent with 10 files inside. I get 8 downloaded before the tracker goes dead. At that point, it would be good for the client to auto-search for the hashes of the two remaining files and offer to download them from another torrent/tracker if one exists that has the hashes of the incomplete files.

Am I missing something that makes this unrealistic?