They Can't Be So Stupid... Can They?

[Collimatrix]

This article had made the rounds earlier on the Sturgeon's House Teamspeak and elsewhere, and was roundly and soundly mocked.  Weaponsman had some fun with it as well.  The authors have, bless their hearts, stuck to their guns and kept the article up, albeit edited for "greater technical clarity."

The mistake the authors are making; a mistake obvious to anyone with a high school understanding of physics, is that re-arranging subatomic particles is quite qualitatively different than re-arranging atoms and molecules.  The authors cite, with breathless anxiety, the fact that 3D printers are able to manipulate smaller and smaller chunks of matter.  Surely the ability to arbitrarily re-arrange matter is just around the corner!

 

Back in the real world, we know that "atoms" are well-named.  While they are not exactly un-cuttable, as the Greek etymology of the word suggests, the forces that bind the nucleons of an atom together are several orders of magnitude greater than the forces that bind the electron shells of atoms together to make molecules and metals.  Any mucking around with the arrangement of the nuclei of atoms is going to either take or produce an enormous amount of energy.  This is what makes nuclear weapons so scary in the first place.

 

So, any civilization that could casually re-arrange matter on the subatomic level would regard our fission weapons with approximately the same consternation as they would a sharpened flake of obsidian.  They would be capable of much scarier things than silly little toys like nukes.

 

The writers go on, incoherently, to point out that 3D printing could conceivably be used with fissile materials.  This is technically true, I suppose, although fissile materials have somewhat tricky physical properties such as multiple phase changes, and pyrophoricity.  Also, bomb cores need to be manufactured to such extreme tolerances that it's unclear what 3D printing would gain you.  And all of this of course begs the question of where said fissile material would come from in the first place.  Which the article never answers.  Because its authors know nothing about nuclear physics.  Because they are poly sci majors, and poly sci doesn't teach you anything useful about anything.  Sorry poly sci majors; you just wasted years and untold kilobucks on a completely useless education.  Better luck next time, and don't burn yourself on the deep fryer racks; that smarts like a motherfucker.

 

This isn't even getting into the fact that the 3D printing revolution is not just around the corner; it's already here.  Additive manufacturing techniques are already used in the manufacture of important things like turbine blades and aerospace fasteners.  Typically, hand-wringing about some great advance in technology that has social implications works better when the great advance is still in the future.  That way you can make wild and absurd predictions and they're basically unfalsifiable if you word them correctly.

 

But that's enough making fun of the poor, dumb bastards who wrote this thoroughly idiotic article.  They're just victims of the education system.  Nobody seriously believes that the technology to manipulate smaller and smaller amounts of electrical bonded matter presages the ability to manipulate subatomic matter arbitrarily, right?

Sadly, wrong.  There is an entire field of study devoted to misunderstanding the implications of micro-manufacture.  It's called nanotechnology.  The entire field is, so far as I can discern, either outlandish claims based on bad analogies, or mundane discussion of what is already routine.  Scott Locklin provides an excellent general fisking here, while specific problems with some of claims made by nanotechnology proponents are tackled at LessWrong here.

 

The derp is everywhere.  Sometimes it will appear wearing the uniform of someone knowledgeable.  Trust... but verify.

[Toxn]

I saw this as well and kind just shrugged my shoulders.

 

I mean, how do you respond to something so clearly wrong beyond pointing out the fact that the writer is an idiot?

 

As for nanotech, the researchers I've talked to are mostly pissed off that their rather fiddly materials science work keeps getting hijacked by people who think that magic anything-machines are just around the corner. Of course, hype about magic anything-machines does a lot to assure them of future funding, so...

[Donward]

ChickenNuclear Weapons... Good.

 

[Priory_of_Sion]

[Sturgeon]

rawrhgeblargerhaaahahwhrhrabbaaaaaad

 

Nanotech is one of those things I've always felt was pretty dumb (though Prey is a great book), and didn't take very seriously, but I admit that is a far, far worse situation than I thought. I had always assumed it was like those stupid people who "make nuclear reactors in their basement" who get featured in PopSci and Wired, not a serious pseudoscientific money hole.

[Tied]

hahaahaha, colli trying to foster intellegent discussion just gave me a exuse to rewatch The Star Wars hahahahaha

[LostCosmonaut]

So exactly how does this Washington Post nuclear printer work? Does it just fuse larger and larger nuclei together until you get U-235? In that case, in less you input a shitload of energy (and also magically handwave away all the other issues), all you'll end up with is the world's most expensive and inefficient iron mine (with slight bit of nickel contaminating the ore).

[Toxn]

I think it's supposed to lay on uranium until your print bed explodes.

[Walter_Sobchak]

It seems that they have confused 3D printing with the replicators from Star Trek.  

[Donward]

Knowing how my normal printer works, there'd be some sort of jam.

 

[Sturgeon]

[Toxn]

Serious question: even assuming pure U-235 and sufficient mass (~60kg); wouldn't you just get a fizzle?

At arm-propelled speeds, I'd think you'd just end up with a self-disassembled 'reactor' which consists of heavily burned/irradiated human bits and sub-critical chunks of uranium.

[Collimatrix]

Serious question: even assuming pure U-235 and sufficient mass (~60kg); wouldn't you just get a fizzle?

At arm-propelled speeds, I'd think you'd just end up with a self-disassembled 'reactor' which consists of heavily burned/irradiated human bits and sub-critical chunks of uranium.

 

Pretty sure you'd get a fizzle.  Core assembly has to be very fast indeed.  How fast?  Quoting from The Nuclear Weapons Archive:

 

 

 

The amount of time taken by each link in the chain reaction is determined by the speed of the neutrons and the distance they travel before being captured. The average distance is called the mean free path. In fissile materials at maximum normal densities the mean free path for fission is roughly 13 cm for 1 MeV neutrons (a typical energy for fission neutrons). These neutrons travel at 1.4x10^9 cm/sec, yielding an average time between fission generations of about 10^-8 sec (10 nanoseconds), a unit of time sometimes called a "shake". 

 

 

and

 

 

We find that both the number of neutrons present in the assembly (and thus the instantaneous rate of the fission reaction), and the number of fissions that have occurred since the reaction began, increase at a rate proportional to e^((k-1)*(t/g)), where e is the natural log base (2.712...), g is the average generation time (time from neutron emission to fission capture), and t is the elapsed time.

If k=2, then a single neutron will multiply to 2x10^24 neutrons (and splitting the same number of atoms) in roughly 56 shakes (560 nanoseconds), yielding 20 kilotons of energy.

 

 

The above "fact" also ignores the fact that proper nuclear weapons don't just sit around and wait for neutrons from spontaneous fission in the fissile core to start the chain reaction; they have devices to get things going crisply.

 

Good god that's bad Sturgeon; where did you find it?

[SuperComrade]

Don't you just end up with something like the Demon Core if you stick those two blocks together?

[Collimatrix]

Except that you might not be able to flop the two pieces apart and make them sub-critical again like the second time they fucked with the demon core.  But yeah, it wouldn't be anything remotely like the core assembly of a proper weapon.

[Toxn]

So, related question: as I understand it the problem with thin man was that the impurities in the reactor-made plutonium would have resulted pre-ignition and fizzle of the device given the assembly speed of 900m/s. Just for interest, what speed would it require to get a gun-type plutonium weapon to work? As a bonus, the resulting weapon (if such were possible) would almost certainly be called Slenderman.

[Khand-e]

Memory serve me, the Thin Man prototype basically proved the concept of a plutonium fueled gun based design is nearly impossible for various reasions, among them relevant to your comment were that the distance required to launch plutonium at a speed great enough to avoid pre detonation (due to it's very high spontaneous fission rate) would require the "barrel" to be so long it wouldn't even be practical to put a weapon the size it would need on any bomber including upcoming designs, even the massive B-36. (Though, I'm not sure the exact speed they calculated it to be.)

[Toxn]

Memory serve me, the Thin Man prototype basically proved the concept of a plutonium fueled gun based design is nearly impossible for various reasions, among then relevant to your comment were that the distance required to launch plutonium at a speed great enough to avoid pre detonation (due to it's very high spontaneous fission rate) would require the "barrel" to be so long it wouldn't even be practical to put a weapon the size it would need on any bomber including upcoming designs, even the massive B-36. (Though, I'm not sure the exact speed they calculated it to be.)

I'm imagining a light gas gun built to last just long enough to fling the critical mass together. It would be huge and stupidly primitive, but very easy to construct.

 

How feasible my imaginings are depends, of course, on just what speed you'd need to achieve assembly.

[Collimatrix]

Memory serve me, the Thin Man prototype basically proved the concept of a plutonium fueled gun based design is nearly impossible for various reasions, among them relevant to your comment were that the distance required to launch plutonium at a speed great enough to avoid pre detonation (due to it's very high spontaneous fission rate) would require the "barrel" to be so long it wouldn't even be practical to put a weapon the size it would need on any bomber including upcoming designs, even the massive B-36. (Though, I'm not sure the exact speed they calculated it to be.)

 

 

Correct.  All fissile materials will, rarely, spontaneously decay via fission and produce neutrons.  This is really obnoxious if you're trying to make a bomb.

 

Per the Nuclear Weapons Archive:

 

 U-235 has a spontaneous fission rate of .16 fission/sec-kg; the lowest of any fissile isotope used in weapons.  U-238 will produce 5.51 fissions/sec-kg, so for a gun-type weapon to work your enrichment facilities had better be up to wringing that stuff out if you want a viable gun-type bomb.

 

Pu-239 has a spontaneous fission rate of about 10 fission/sec-kg, and the contaminant isotope Pu-240 (which is difficult to remove with current enrichment technology because of the extremely close mass ratios) has a whopping 415,000 fission/sec-kg.  Pu-242 has an even higher spontaneous fission rate of 840,000 fission/sec-kg, although this isotope is typically only present in substantial quantities in reprocessed fuel (this is just one reason that the Carter Administration was full of shit when they said that fuel reprocessing posed a proliferation threat).

 

Assembly of the core, and taking the fissile material from a sub-critical state to a super-critical one must occur quickly enough that all these naturally occurring neutrons can't cause trouble.  Implosion-type cores achieve this on the order of a few microseconds, while gun types require about a millisecond.  

 

 

So, yeah, you could totally cause a nuclear explosion by slamming two pieces of U-235 together with your hands... assuming you can slam the metal together hard enough that it fuses and becomes one piece in about a millisecond.  Obviously, doing the nuke party trick would be a last resort for someone that strong, since they could probably just chop tanks in twain with their bare fists.

[Collimatrix]

These idiots never quit.

[Toxn]

These idiots never quit.

In fairness to idiots: the UK shows that, if you cannot absolutely stop criminals from having guns, you can at least force them to have shitty ones. I'm sure their Queen, for one, is pretty happy about the state of gun ownership there - getting shot at with blanks sure beats getting shot at with live rounds.

 

Unfortunately, it seems like the price for forcing crims to use shitty guns is that you have to live on an island and stop absolutely everyone else from having guns too.