It might be worth noting that a Hydrogen bomb is also an atomic bomb. That is, in order for a Hydrogen bomb to detonate they wrap an Atomic bomb around the outside. The fusion process in a Hydrogen bomb is difficult to start and requires the intense pressure and temperatures created by the Atomic bomb explosion to kickstart it into action. This is why you still get radioactive fallout from a Hydrogen bomb. If you could detonate the Hydrogen bomb sans the Atomic bomb there would be no radioactive fallout (since hydrogen is not radioactive in the same sense that Plutonium/Uranium is).
If we could get a fusion reaction going using hydrogen, would that produce energy without radioactivity or radioactive waste?
I realize that nuclear reactors are not using fusion, but if we can invent a practical fusion power plant, a lot of our problems as a species could be addressed.
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What’s the difference between a hydrogen bomb and an atom bomb? (12-Jan-1996)
moderator, Comments on Cecil’s Columns
Shodan, the following information from Scientific American’s “Ask The Expert” column may interest you:
The authors of the replies are, as one might expect from such a forum, sanguine about the benefits of a commercial fusion power plant, but do not foresee one in the near future.
I think that fusion bombs/reactors use deuterium and tritium, two (heavier) isotopes of hydrogen. Hydrogen has one proton in its nucleus; deuterium, one proton, one neutron; tritium, one proton and (yes, you guessed it) two neutrons.
When these two atoms undergo fusion, two protons and two neutrons form the nucleus of one atom of helium, which is not radioactive. The third/extra neutron is converted into energy.
So I don’t think fusion produces radioactive atoms, but tritium itself is radioactive. However, I’m not sure how “dangerous” tritium is; it’s used in luminescent clock and watch faces (because it will last a long time) which leads me to believe that, in small quantities, its radioactive effects are negligible. Assuming this is true, fusion is definitely cleaner and “greener” than fission.
Actually, they use lithium deuteride of varying concentrations of Li-6 and Li-7 isotopes for the reasons that lithium deuteride has more hydrogen per volume than even liquid hydrogen, and because through various reactions, the lithium gets involved, producing tritium, which is the preferred fusion fuel.
That’s why the Castle Bravo test(first lithium deuteride fueled) overshot the predicted maximum yield by a factor of 2. The scientists didn’t account for the Li-7(natural)fusion in their calculations.
From http://www.fas.org/nuke/hew/ :
(THE page for info on nuclear weapons)
**
The most important fusion reactions for thermonuclear weapons are
given below:
- D + T -> He-4 + n + 17.588 MeV
- D + D -> He-3 + n + 3.268 MeV
- D + D -> T + p + 4.03 MeV
- He-3 + D -> He-4 + p + 18.34 MeV
- Li-6 + n -> T + He-4 + 4.78 MeV
- Li-7 + n -> T + He-4 + n - 2.47 MeV
[D and T stand for deuteron or deuterium (H-2), and triton or tritium
(H-3) respectively.]
**
But… generally speaking, around 50-90% of the yield of a thermonuclear weapon is due to the fast-fission of the uranium tamper of the fusion stage by fusion neutrons.
All those neutrons zinging around in a fusion reaction do induce some radioactivity in things around them, and do some damage on their own, but the byproducts of the reaction aren’t hazardous, unlike fission by-products.
Tritium has a half-life of about 12 years, and is a very weak beta particle emitter, so thin layers of almost anything can shield from its radiation, hence its use in watch faces, etc…
Arnold
Sorry about the slip. Thanks for catching and rectifying the situation.
Shodan
I believe MJH2 is partly right although I thought deuterium is the preferred fuel for a fusion reactor on not Tritium. I certainly could be wrong on this though (I haven’t had a chance to read the Sci Am article Arnold linked).
That said Fusion reactors to produce electricity are the Holy Grail of energy production. The fuel, basically found in seawater, is VERY abundant and easy to get at (no drilling holes in the ground and what not). The byproduct of a fusion reactor is helium, an inert gas and about as harmless as you can get (although we might all talk funny if they spew the helium in the atmosphere).
The best part…NO radioactive waste. The fusion reaction itself sends off all sorts of things nasty to humans (gamma rays, alpha and beta particle emissions, etc.) but none of that should ever make it out of the reactor’s containment vessle.
So…we have a clean, abundant form of energy here. So what’s the problem?
Basically starting a fusion reaction takes a HUGE amount of energy (as mentioned in the OP). So far, scientists can start these reactions in the lab (without resorting to atomic bombs) but they end up putting more energy into the system than they can extract (i.e. I put 100 watts in to start the thing but I only get 70 watts out before the reaction stops running).
Of course, the way around this is to keep adding fuel once you’ve started the reaction…like working hard to start a campfire and then doing nothing more than tossing another log on now and then to keep it going. Unfortunately the temperatures that the plasma is at is high enough to melt any earthly material. To keep the whole thing from melting the power plant the reaction is contained in a magnetic bottle so the plasma ‘floats’ without actually touching anything. So far so good but how do you add more fuel? How do you remove the helium waste product? Shut down the magnets for an instant and the extremely high pressurized plasma will burst out…not a pretty scene.
So…scientists keep working on this because the potential is so great if it ever becomes practical. Someone in another thread (in GQ I think) said that scientists have been promising a working fusion reaction in maybe 20 years for the last 50 years.
Who knows…maybe someday.
Well, it sounds like bump is your man with the Goods.
Thanks, bump!
Correct me if I’m wrong, but an atomic bomb doesn’t bust big atoms into little atoms. It busts atoms into subatomic particles. Am I the only one who caught this?
It busts them into both. I don’t remember the specifics, but a U235 nucleus splits into two smaller nuclei (potassium and krypton?), plus three neutrons. The neutrons are what triggers the next uranium atom to split, and keep the chain reaction going. If you split it entirely into its constituent protons and neutrons, you’d have to put in more energy that you could get out.
Chronos is right- fission(a la Fat Man & Little Boy) split U or Pu atoms into smaller ones & neutrons.
Fusion bombs(otherwise called thermonuclear) use a smallish fission bomb to rapidly compress a fusion fuel package & start fusing it. In a “clean” fusion bomb, the majority of the radioactive byproducts are due to the fission primary, not the fusion part fo the reaction. As a notable point, the Tsar Bomba(50mt) was both the largest & cleanest bomb ever detonated, with 95% of that 50mt coming from fusion reactions.
I stand corrected.
There are several pairs of atoms that can result from a fission reaction. Many are quite hot in their own right--that's what the majority of the fallout is.Oddly enough, a slim possibility exists for a direct to fusion weapon. This device would use a very energetic chemical explosive to compress a fusion core to ignition.
Some estimates allow for a bomb the size of a grapefruit. While the direct blast effects should be on the order of a car bomb, immediate lethal radiation effects should extend out 2 to 4km.
BTW, as the weapon emits very low levels of easily screened radiation, it would be very difficult to detect.
Rest assured, dedicated researchers are working on both the weapon and the detection of the weapon.
Not “also”. That’s like saying an atomic bomb is “also” a high-explosive chemical bomb. There’s no also to it–in both situations, the latter is the trigger for the former, and is relatively insignifigant as a part of the total yield.
As for the parenthetical bit at the end–Helium is what’s left over from a thermonuke (H-bomb)…Hydrogen is the starting product, and is fused into Helium.
I know, it’s kind of nitpicky, but I’m a stickler on bombs.
And bump–I’m not complaining, but the fusion reaction formulas would’ve benefitted from the use of [sup]sup-[/sup] and [sub]sub-[/sub] -script tags.
I was under the impression that both deuterium and tritium were important for efficient hydrogen fusion. We were told that that was what made Lithium deuteride so nifty hit lithium with a bunch of high speed neutrons, and bingo brand new tritium since tritium has a half-life far shorter than deuterium it works better to make most of it “on demand” so to speak. deuterium lasts a lot longer and weapons don’t constantly require maintenance of fussionable supplies.
Also Fallout. Fallout is what you get from a ground burst when radioactive bits of dirt and ash settle out after a blast. A fusion bomb can create as much fallout as a fission bomb, probably more since they are generally much more powerful.
The way to avoid creating fallout is to go for an airburst. An airburst is also more efficient since you’re not wasting all that energy tossing dirt into the air, you’re using it to knock down buildings and incinerate people.
Actually, the reason an airburst is more efficient is that an atom bomb is overkill--whatever is hit is hit with far more energy than neccessary to destroy it. An airburst spreads the blast energy out better--the target isn't hit as hard, but more area is hit hard enough to destroy.
It also has the advantage that there isn't that much stuff near the bomb to be transmuted into radioactives. Furthermore, what radioactives that are created stay in the atmosphere longer--more chance to decay before they fall down and are dangerous.