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Natural Science Forum / Physics / Particle Physics / October 2004Nuclear decay post-detonation
I'd like to know what options there are for ensuring that a nuclear missile doesn't leave the site where it's detonated radioactive after the blast. I think with conventional ICBMs the ground where they impact will be left radioactive for decades (if not longer), due to the long half lives of the the nuclear materials. So is it possible to build a nuclear warhead with a shorter half-life so that it doesn't leave too much radioactivity in its aftermath, but without compromising its destructive force? PS: This is a just a *scientific*, educational, exploratory research question... don't think too much of my plans with this please! Thanks AAI that was the idea behind the neutron bomb. kill people but not contaminate the area. > I'd like to know what options there are for ensuring that a nuclear > missile doesn't leave the site where it's detonated radioactive after [quoted text clipped - 12 lines] > Thanks > AAI > that was the idea behind the neutron bomb. kill people but not contaminate > the area. A neutron bomb wont work for the *space* applications I have in mind... I'd like to hollow out an asteroid by detonating nuclear missiles into it to carve out some living space inside it, as depicted here: http://uk.geocities.com/aa_spaceagent/restricted/interstellar-propulsion.html I don't want that excavation to become radioactive, as I'd like to turn it into a living habitat for people, plants and animals functioning as a miniature biosphere. Is there another kind of heavy duty blast mechanism that could be used instead of outright *nuclear*? > > that was the idea behind the neutron bomb. kill people but not contaminate > > the area. [quoted text clipped - 12 lines] > Is there another kind of heavy duty blast mechanism that could be used > instead of outright *nuclear*? Ah, and in that case I have to disillusion you some more. A blast does not make matter disappear. It may heat it to a gas and send it in all directions at enormous speeds, but the matter is still there -- all over the countryside in fact. So if you set off a bomb inside a small hole to make a bigger hole, you have to ask, "Where is all this STUFF going to go?" Unless you have a good way to channel the explosive debris out to the outside, chances are you are only going to split the rock, or at the very least open a big channel from the outside to the inside. To get a feel for what's involved, look up the engineering requirements for underground mine blasting and where all that "stuff" goes. You stand a better chance of landing on the rock and digging, as in a mine. PD >Ah, and in that case I have to disillusion you some more. A blast does >not make matter disappear. It may heat it to a gas and send it in all >directions at enormous speeds, but the matter is still there -- all >over the countryside in fact. >So if you set off a bomb inside a small hole to make a bigger hole, >you have to ask, "Where is all this STUFF going to go?" Unless you >have a good way to channel the explosive debris out to the outside, >chances are you are only going to split the rock, or at the very least >open a big channel from the outside to the inside. I have seen photos of a cave created by an underground nuclear explosion. The ceiling was hemispherical so apparently a spherical "bubble" was created. The bottom of the cave was filled to about the halfway point (maybe somewhat more) with rock/rubble so about half the volume was left. I don't know what happened to the rest of the rock, but I'll guess that the density of the rock in the walls was increased by compression.  Signature-Mike > So if you set off a bomb inside a small hole to make a bigger hole, > you have to ask, "Where is all this STUFF going to go?" Unless you > have a good way to channel the explosive debris out to the outside, > chances are you are only going to split the rock, or at the very least > open a big channel from the outside to the inside. I would assume the material exploding *outwards* from the detonation simply finds any open spaces to get out... which would be the direction where the missile goes in! If the hole is engineered to be kept nearly as *wide* as it is deep, then surely material would just find its way out, much like the stuff coming out of a meteorite crater after impact. > You stand a better chance of landing on the rock and digging, as in a > mine. Asteroid mining is set to become HOT business in the future, so some digging would be involved any way. So what other *non-nuclear*, highly destructive blast options are available do you think? Abdul > > So if you set off a bomb inside a small hole to make a bigger hole, > > you have to ask, "Where is all this STUFF going to go?" Unless you [quoted text clipped - 8 lines] > find its way out, much like the stuff coming out of a meteorite crater > after impact. Ah, perhaps I misunderstood. I thought you wanted a hole in the INTERIOR of the asteroid (that is, completely surrounded by rock, except perhaps for a pluggable access tunnel), as opposed to a hole on the SURFACE of the asteroid. Here's another way to think of it. Hand grenade dropped on the ground makes a big hole in the ground. Hand grenade buried deep in ground makes a tiny hole under ground. PD pdraper@yahoo.com (Paul Draper) wrote in message > Ah, perhaps I misunderstood. I thought you wanted a hole in the > INTERIOR of the asteroid (that is, completely surrounded by rock, [quoted text clipped - 4 lines] > Hand grenade dropped on the ground makes a big hole in the ground. > Hand grenade buried deep in ground makes a tiny hole under ground. This might help: http://uk.geocities.com/aa_spaceagent/restricted/earth-ring.html Here I show a dark hole already in the making after a few initial blasts. AAi > I'd like to know what options there are for ensuring that a nuclear > missile doesn't leave the site where it's detonated radioactive after [quoted text clipped - 12 lines] > Thanks > AAI No, it's not possible. Nuclear warheads use fissile material because, well, that's how a nuclear bomb works (both fusion and fission). All fissile materials suitable for chain reactions have long-lifetime radioactive products, not to mention the material scattered that did not ... did not... (what's the verb for fission?) ... fiss. Think of it this way. If all the radioactive material were short-lived, then it would decay in the missile silo before you had a chance to launch it. PD > > I'd like to know what options there are for ensuring that a nuclear > > missile doesn't leave the site where it's detonated radioactive after [quoted text clipped - 6 lines] > short-lived, then it would decay in the missile silo before you had a > chance to launch it. I'm not sure I understand what you mean. From what little I *think* I know about the workings of these bombs, the pre-fission material stays intact inside the missile until it reaches its point of detonation. The detonation and the fission process are triggered at the point of impact. What I am then saying is that the by-product post detonation (post-fission) is radioactive with an extended half life, and I'd like to have that half life shortened so that the unwanted radioactivity doesn't linger. With so many radioactive isotopes to pick and choose from, is it not possible to find one that "fissions" with a residue of a desirably shorter half life? Thanks AAI <snip> > With so many radioactive isotopes to pick and choose from, is it not > possible to find one that "fissions" with a residue of a desirably > shorter half life? > > Thanks > AAI My point was, I don't think so. Certainly not every radioactive isotope "fissions" at all. Fission is a special process available only to high mass nuclei. (Alpha and beta decay are much more common processes.) Secondly, not every isotope that can be "fissioned" will sustain a chain reaction. A chain reaction requires a detailed balance between neutron emission from the fission, neutron moderation, and neutron recapture cross-sections. Among other things, that's why a mine full of uranium ore doesn't detonate on its own. There are in fact only a handful of isotopes that are capable of a fission chain reaction, and only a few of them have long enough lifetimes themselves to not decay spontaneously in a missile warhead, and I don't know of any that don't have long-lifetime post-fission products. >>>I'd like to know what options there are for ensuring that a nuclear >>>missile doesn't leave the site where it's detonated radioactive after [quoted text clipped - 15 lines] > to have that half life shortened so that the unwanted radioactivity > doesn't linger. N.B. Don't forget that *shorter* half-life means *higher* radiation. > With so many radioactive isotopes to pick and choose from, is it not > possible to find one that "fissions" with a residue of a desirably > shorter half life? You don't really get to pick and choose fissile material. It takes very specific properties to allow for a chain reaction fast enough to lead to an explosion. Basically, all fission bombs are based on one of two reactions U235 + n -> (fission products) + neutrons + energy OR Pu239 + n -> (fission products) + neutrons + energy In both cases, the extra neutrons trigger more fissions, but the fission products are determined by nature, not by the designer. -E > Thanks > AAI >> With so many radioactive isotopes to pick and choose from, is it not >> possible to find one that "fissions" with a residue of a desirably >> shorter half life? >You don't really get to pick and choose fissile material. It takes >very specific properties to allow for a chain reaction fast >enough to lead to an explosion. Are there other isotopes that could theoretically be used in a bomb? We all know of U-235 and Pu-239, and I know U-233 also fissions. Are there others? I suspect any others are of the type that would "decay before the missile was launched". Signature-Mike >>>With so many radioactive isotopes to pick and choose from, is it not >>>possible to find one that "fissions" with a residue of a desirably [quoted text clipped - 6 lines] > Are there other isotopes that could theoretically be used in a bomb? > We all know of U-235 and Pu-239, and I know U-233 also fissions. Lots of things fission. The essential property you're looking for is something that's pretty stable until it captures a neutron, and then becomes very unstable. I believe the U233 could also work, but it has essentially zero occurence in nature. When they were building the original A-bomb, they focused on Plutonium and Uranium because - - U235 occurs naturally at about .75% of Uranium ore, BUT must be separated by a mass spectrometer - Pu239 is copiously produced in nuclear reactions, and can be *chemically* separated from Uranium, which is much easier than isolating U235. At the time, they also considered Protoactinium and Thorium, but the former is very rare and Thorium had no real advantage over Uranium. In recent years, Thorium has been investigated as an energy source, and I know that India at least has a major R&D program: http://www.world-nuclear.org/info/inf62.htm I don't know about it's potential as a weapon. It's extremely unlikely that any fission bomb would yield particularly safe fission products. -E > Are > there others? I suspect any others are of the type that would "decay > before the missile was launched". > >>>With so many radioactive isotopes to pick and choose from, is it not > >>>possible to find one that "fissions" with a residue of a desirably [quoted text clipped - 11 lines] > and then becomes very unstable. I believe the U233 could also > work, but it has essentially zero occurence in nature. one more thing necessary to sustain a reaction... when it fissions it must produce more neutrons than it captures... and preferably in the right energy range, not all isotopes absorb 'fast' neutrons to fission, but they do create them... if the neutrons are too fast from the fission they must be slowed down by some other material or the reaction won't continue. >> Are there other isotopes that could theoretically be used in a bomb? >> We all know of U-235 and Pu-239, and I know U-233 also fissions. >Lots of things fission. The essential property you're looking >for is something that's pretty stable until it captures a neutron, >and then becomes very unstable. I believe the U233 could also >work, but it has essentially zero occurence in nature. >When they were building the original A-bomb, they focused on >Plutonium and Uranium because - [quoted text clipped - 3 lines] > can be *chemically* separated from Uranium, which is > much easier than isolating U235. >At the time, they also considered Protoactinium and Thorium, but >the former is very rare and Thorium had no real advantage over >Uranium. >In recent years, Thorium has been investigated as an energy >source, and I know that India at least has a major R&D >program: >http://www.world-nuclear.org/info/inf62.htm >I don't know about it's potential as a weapon. As I understand it, thorium won't fission by itself but if loaded into a nuclear reactor, thorium captures neutrons and decays into U-233, which will fission, and can be separated chemically. Exactly like U-238/Pu-239. The U-233 could be put back into a reactor as fuel. But supposedly a U-233 bomb is very difficult to do. I've read only one has ever been set off, and pretty much only to see if it could be done. I was wondering if isotopes of some heavier elements like americium or curium would work in a bomb even if it was very difficult to do due to short half-lives. Signature-Mike > >>>I'd like to know what options there are for ensuring that a nuclear > >>>missile doesn't leave the site where it's detonated radioactive after [quoted text clipped - 17 lines] > > N.B. Don't forget that *shorter* half-life means *higher* radiation. One final question. Suppose the missile (or several missiles - compounding the destructive effect incrementally) are exploded on a hard, granite type of bedrock strata several square miles in area. Post-detonation, the area is left with a large hole whose interior rock surface is radioactive due to the post-fission debris. If now you wanted to make the hole safe for building a habitat shelter within it suitable for people to live in, how much rock (to what depth) would you need to excavate out of it to get rid of the lingering radioactiveness? This is to make it *completely* safe? Thanks AAI |
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