Heh. Badly paraphrased from memory…
Outsider “For another million stars, we’ll tell you the exact nature of the anomaly.”
Elephant “Won’t we discover it for ourselves?”
Outsider “It is likely.”
Johnny L.A. You’re probably thinking of these…
The U.S. Army used to have an 8-inch nuclear artillery shell that was produced in large numbers and produced multi-kiloton yields. I believe it used U235 and gun assembly.
Heh again. And later on, also paraphrased:
Elephant: “I want to register a complaint about my General Products hull! <description of bizarre inexplicable accident>”
Puppeteer (logically deducing the problem in a heartbeat): “Our apologies are inadequate, of course, but… we had no idea that antimatter was available in this galaxy.”
Elephant and Shaeffer (likewise having had no idea): “Gah!” :eek: :smack:
That’s it. Thanks.
Okay… I’ve gotta ask - what is this from?? On a google-guess, is it by any chance ‘flatlander’?? 
You’re thinking of the Davy Crockett. (There was also the SDAM, which was a “backpack” version of this device.) This is the smallest openly acknowledged device in the American nuclear arsenal. However, physicist Ted Taylor, who was the principle researcher on advanced fission and boosted fission-type, suggested to John McPhee (see The Curve of Binding Energy) among others that he’d at least conceptually designed a device that could fit in the palm of one’s hand–say, the size of a softball. Whether such a device was ever fabricated or tested he was close-mouthed about, but it is concievably possible to do so, even without resorting to unstable exotic transuranics like californiam and americium. Note that these are likely to be boosted designs; in other words, the initial pulse of neutrons, after explosive compression, generates a side-reaction with lithium deutride or some other substance that creates a huge mass of neutrons, making the overall reaction more efficient in terms of total fissions before the core blows itself apart.
Turner became interested in such small munitions as part of the Project ORION. The problem with ORION is that using “bomblets” the size of conventional munitions mandated a ship of massive minimum size and produced a lot of radioactive waste. A more compact bomblet translated into a smaller vessel, less robust two-stage shock absorber, and generally easier handling. ORION, of course, never got off the ground, and Turner became an advocate for nuclear disarmerment and alternative energy later in his career.
Others have addressed this, but I don’t think it has been made adequately clear; the notion that fission is some kind of kinetic reaction in which a neutron “splits” the nucleus of an atom is conceptually incorrect, despite the nomenclature. What happens is that a nucleus “captures” a neutron, becomes unstable (for reasons that are too complex to go into here…basically, the math doesn’t add up), and fissions into two smaller nuclei and various products, like neutrons and ionizing radiation depending on the composition of the original nucleus. This capture event is a statistical occurance based upon the something called the neutron capture cross-section (basically, the likelyhood that the neutron will intersect the nucleus–think of it as an analog to diameter, hence “cross-section”) and the energy of the neutron; counterintuitively, the lower the energy of the neutrons, the more likely it to fission, which is why moderators (water, graphite, et cetera) are used.
With small cores the neutron flux is small, because there are fewer neutron sources to begin with. In order to make a small core work you have to compress it dramatically (to increase flux) and reflect escaping neutrons back toward it; and you have to do all of this very quickly, in a couple of shakes. This is a tricky, tricky problem and only fine control of the containment explosion and the most tightly controlled manufacturing tolerances will permit a controlled compression. This is developed by extensive testing in combination with advanced hydrodynamic (elasto-fluid) modeling simulations. It’s unlikely some up-and-coming nuclear power with limited resources could build, say, a grapefruit-sized package, but it’s virtually certain that the US, and probably the former Soviet Union, could if not did build weapons of such size or smaller.
Golf-ball sized would be tricky and likely inefficient, but plausible with sufficient resources and testing. Bullet-sized packages are unlikely without resorting to exotic actinoids produced in miniscule quantities at enormous effort and cost.
Stranger
Yes. Shaeffer and his tycoon buddy Elephant discover a planet made of the only thing that can disrupt a macromolecular GP hull. Though you’d think that a disruptor–which suppresses the electric charge on the proton or electron–would tear a GP hull apart too. Oh well, yet another inconsistancy[sup]*[/sup] in the Known Space universe.
Stranger
*The Ringworld is unstable.
OK, perhaps my understanding of nuclear physics is very poor, but Hydrogen has one proton and Helium has two. The element is defined by the number of protons. Therefore, two hHydrogen atoms make one Helium atom, not four.
Not quite. Neutronium is only stable in a neutron star. If you somehow managed to remove a lump of neutronium from a neutron star, the neutronium itself would explode, probably significantly more powerfully than the nuke you’re trying to trigger.
flight, a (normal) helium nucleus only has two protons, but it also has two neutrons, which have to come from somewhere. You can start with two deuterium nuclei (deuterium being an isotope of hydrogen with one proton and one neutron) to get a helium, or a normal hydrogen and a tritium (hydrogen with a proton and two neutrons). Or you can start with four hydrogens, and through various nuclear reactions, end up turning two of them into neutrons (strictly speaking, each of the two turns into a neutron, a positron, and a neutrino, but the positron and neutrino are much lighter, and not significant for our purposes). Since normal hydrogen is much more common than deuterium or tritium, it’s this latter reaction which primarily powers stars. Man-made bombs usually use deuterium and/or tritium, however, since it’s much easier to get them to fuse.
This was the reaction I was familiar with. I was not aware of the different nature of nuclear fusion within a star though, interesting.
Note that there are a number of different reactions that occur within a star, falling into two “chains”: the proton-proton chain (D+D -> D+T -> He+He) and the C-N-O cycle which creates heavier products. Fusion reactions can occur all the way up to Fe (iron), although with significantly reduced energy output. Technically speaking, fusion even occurs in elements heavier than iron, although it requires special conditions (the high neutrino flux within an active supernova that permits conversion of neutrons to protons, thus stabilizing neutron-heavy isotops to “heavier” stable elements) and astrophysicists differentiate this by referring to it as synthesis rather than fusion.
As a practical matter (for bombs) the only reactions of concern are the D-D and D-T reactions. Helium fusion makes up only a very small and inefficient portion of the total energy budget, and in fact too high a proportion of helium in the fuel will result in a drastically reduced energy budget as the helium atoms trap free neutrons.
Stranger
(Bolding mine)
Unless, that is, you live in Dan Brown’s universe. Just have CERN whip you up a few grams and deliver it to you with their supersonic biz-jet. (“Angels and Demons”)
Gahhhhh! :rolleyes:
I don’t know about that, but they had a nuclear hand grenade in Voyage to the Bottom of the Sea.
FWIW, I met some of the physicists who worked on the Manhattan Project and saw one of the gold foil separators that were made to be placed between the plutonium hemispheres that formed the core of the implosion device tested at Trinity and later named Fat Man. (The gold foil was needed because the flat surfaces of the two hemispheres were so precisely machined that if you put them together for any length of time, they would essentially “weld” together and become impossible to separate. At least, that’s my recollection of the explanation I got more than 20 years ago.)
My reading up to that point had led me to believe that the core was about the size of a grapefruit, i.e. about 5 or 6 inches in diameter. I was a little surprised to see that it was actually about half that. So a hollowed sphere of PU 239 just under 3 inches is a subcritical mass capable of a yield of 20 KT.
As the picture in the link above shows, the actual gadget was about seven feet in diameter and weighed a couple of tons. All of that was to contain the shaped explosive charges needed to compress the core to a supercritical mass, as well as the uranium damper, firing circuitry, etc.
Although advances in explosives and electronic technology would undoubtedly permit some miniaturization, you would probably still have to start with a core larger than a golf ball, even if you used neptunium or californium, which have smaller critical masses than plutonium.
The term “critical mass” is something of a misnomer; you can, and in fact, modern weapons do use subcritical masses by imploding them to high density and using neutron reflectors to enhance neutron flux. Also, boosted designs (that is, those that use incomplete fusion to produce neutrons to enhance fission) can increase the yield over the same mass of a pure fission bomb by several times.
A nuclear hand grenade would still be a very silly idea, though.
Stranger
A suicide bomber might find one useful. :eek:
Uhh, yep, to take this to the basics…
Even if such could be accomplished, you ain’t getting Mrs. LiveOnAPlane’s little boy to toss one of those!
I can’t throw anything 10 or 20 miles, sorry.
I understand that, but there must be a lower limit to the amount of fissile material needed to obtain a fission reaction, even assuming ideal conditions. For instance, a golf ball has a diameter of 1.68 inches (4.27 cm), so if I’ve done the math right, a sphere of PU-239 that size would have a mass of about 616 grams, about 1/16th the amount needed for a critical mass sphere. Could that small a mass be pushed into even a little fission explosion?
I paersonally always wondered if for a more conventionally launched munition you could make a shell that the impact of the projectile crushed a hollow charge of some kind of weapon grade radioactive material into a tight enough ball to go critical. If this was the case you could literally make a hollow bullet of the stuff or jacket it with lead, copper, whatever as needed.
Nuclear rifle bullets, or maybe something akin to a heavy anti tank rifle. People would probably be losy for triggering the charge when hit, but hard surfaces would probably get some pretty hefty divots taken out of them by tiny nuclear blasts.
Could something like that work or is more force than a rifle bullet impact against a hard surface needed?