Atomic Weapons 101

[KarlMarx]

I was watching a series of YouTube videos on nuclear weapons. As far as the Iranians are concerned... this is what is relevant

The bombs that the Iranians are trying to develop are fission bombs that use Uranium-235.

Fission is the process by which the nucleus of a Uranium atom absorbs a neutron, becomes unstable then splits into two lighter nuclei (Barium and Krypton) and emits several neutrons. These neutrons then go on to split other Uranium atoms, which go on to split others, etc. This is called a "chain reaction"

U-235... what is that. There are several types of Uranium, called "isotopes". The difference between these types of Uranium is the number of neutrons in their nuclei. The most common form of Uranium is U-238,which is not good for atomic weapons, but can be used to make Plutonium. Uranium 238 makes up about 99.3% of all Uranium. Uranium-235 is about 0.7% of all Uranium, that is the "weapons grade" stuff.

How do you separate U-235 from U-238? U-238 is slightly heavier than U-235, so if you make a gas that contains Uranium (Uranium Hexaflouride) and put it in a centrifuge, the molecules of the gas with U-235 will separate slightly from the gas with U-238. If you pass that gas through thousands and thousands of centrifuges, you will get a gas that contains a high percentage of U-235. That is why the Iranians have a lot of centrifuges. BTW... centrifuges are easy to conceal... you can have a building the size of a school that has thousands of centrifuges and it would be hard to find.

Making a Uranium bomb (see below)... You need a bomb that has a "critical mass" of Uranium. That is the amount of Uranium you need to sustain a nuclear detonation. On one end of the bomb, you have a ring of a sub-critical mass of Uranium (shaped like a Life Saver candy). On the other end, you have a sub-critical mass that is plug of Uranium on the other end. To trigger a detonation, you use a high explosive to send the plug into the hole of the Life Saver. This will create a critical mass of Uranium, and voila, a nuclear detonation. This type of weapon is a "Uranium gun weapon" and, while it is inefficient (less than 1% of the atoms undergo fission), it is very easy to make. In fact, the Manhattan project did not bother testing Uranium gun weapons because they were very certain the design would work (they were right).

http://myth.greyfalcon.us/pictures/gun20.jpg

[NightTrain]

I fear for Israel's safety with those nutjobs getting ever closer to making a nuke.

Smuggle that in to Gaza, recruit a couple of palestinians, and deny everything.

I'm sure Israel is constantly scanning and sniffing for radiation signatures with high tech surveillance, but wrap enough lead around the bomb's shipping crate and it'll be invisible.

[Gunny]

I fear for Israel's safety with those nutjobs getting ever closer to making a nuke.

Smuggle that in to Gaza, recruit a couple of palestinians, and deny everything.

I'm sure Israel is constantly scanning and sniffing for radiation signatures with high tech surveillance, but wrap enough lead around the bomb's shipping crate and it'll be invisible.

The dumbest thing Iran will ever do is attack Israel with any kind of nukes. It'll be on like Donkey Kong.

[gabosaurus]

I fear for everyone's safety if anyone explodes a nuke. Because any exchange of nuclear weapons destroys civilization. Difficult to believe that any country or leader still thinks a nuclear war in winnable. If you believe otherwise, go watch the movie "Threads." If you can find it. The movie is so realistic and frightened so many people, it's not allowed to be publicly shown anymore.

[Gunny]

I fear for everyone's safety if anyone explodes a nuke. Because any exchange of nuclear weapons destroys civilization. Difficult to believe that any country or leader still thinks a nuclear war in winnable. If you believe otherwise, go watch the movie "Threads." If you can find it. The movie is so realistic and frightened so many people, it's not allowed to be publicly shown anymore.

I don't need a movie. Want to watch a movie? Try Tears of the Sun. THAT is real life that you ignore in favor of your politics.

[Little-Acorn]

Difficult to believe that any country or leader still thinks a nuclear war in winnable.
Well, I'll be damned.

Here we have proof positive of the existence of one person in this world who actually believes some "country or leader" thinks a nuclear war is winnable, and isn't just using their own nukes' existence to deter others.

I thought all these "someone thinks nuclear war is winnable" loonytoons had gone the way of the dodo. But here we have one right in our own forum.

How she managed to evade reality all these years is a mystery.

[Little-Acorn]

KM, not plutonium? It's easier to produce, and Iran is known to have at least one breeder reactor of the type that is designed to produce it. But it's trickier to handle and detonate. In WWII, US scientists found that due to inevitable impurities, slug guns couldn't accelerate it fast enough. They had to come up with a completely new design (implosion method) in WWII to get it to go boom. They made a hollow sphere (I think) of plutonium, then packed several tons of high explosive blocks around it, timing their ignitions to explode simultaneously from outside to inside, crushing the hollow sphere and actually compressing the plutonium metal to a fraction of its original volume. That was enough to get the chain reaction.

When the time came to use them, the US had managed to produce just enough uranium for one slug-gun bomb. The dropped that one on Hiroshima, as you said without needing a test. But they had enough plutonium for two implosion bombs. They had to test that one because they were a lot less sure it would work, so they shot off the first on in the New Mexico desert in July 1945. It worked. They dropped the other on Nagasaki.

Today, most nukes are plutonium implosion bombs, due to its ease (relatively) of production. Even the triggers used to set off hydrogen (fusion, not fission) bombs, are plutonium bombs. I believe the small nukes (artillery shells, backpack nukes etc.) are uranium slug-gun bombs.

[KarlMarx]

KM, not plutonium? It's easier to produce, and Iran is known to have at least one breeder reactor of the type that is designed to produce it. But it's trickier to handle and detonate. In WWII, US scientists found that due to inevitable impurities, slug guns couldn't accelerate it fast enough. They had to come up with a completely new design (implosion method) in WWII to get it to go boom. They made a hollow sphere (I think) of plutonium, then packed several tons of high explosive blocks around it, timing their ignitions to explode simultaneously from outside to inside, crushing the hollow sphere and actually compressing the plutonium metal to a fraction of its original volume. That was enough to get the chain reaction.

When the time came to use them, the US had managed to produce just enough uranium for one slug-gun bomb. The dropped that one on Hiroshima, as you said without needing a test. But they had enough plutonium for two implosion bombs. They had to test that one because they were a lot less sure it would work, so they shot off the first on in the New Mexico desert in July 1945. It worked. They dropped the other on Nagasaki.

Today, most nukes are plutonium implosion bombs, due to its ease (relatively) of production. Even the triggers used to set off hydrogen (fusion, not fission) bombs, are plutonium bombs. I believe the small nukes (artillery shells, backpack nukes etc.) are uranium slug-gun bombs.

Yes, I didn't mention Plutonium-239 because I didn't think the Iranians were making those.

Plutonium-239 is created by bombarding U-238 with neutrons. Which then creates Neptunium-239 and beta decays into Plutonium-239. And you're right, it's easier to make.

And you're right, Plutonium suffers from premature detonation (some guys have that problem too :) ). So Plutonium does not work in a gun weapon type bomb.

For Plutonium, as you said, you need an implosion type weapon which is what we detonated at Alamogordo and dropped on Nagasaki. The advantage is that you don't need much Plutonium for such a weapon, only about 5 or 6 pounds. However, the implosion part is very tricky

The problem with this design is that you must detonate each lens within milliseconds or microseconds of each other, or you don't achieve the implosion you want, you get a pancake or another shape.

From what I've read so far, all nuclear weapons in our stockpiles and, for that matter, other countries are implosion weapons. But, I didn't know we still used gun type weapons... I think your comment about the artillery shells makes sense.

There is a problem with Plutonium, however, it decays by emitting alpha particles. Those are the nuclei of Helium atoms. So you will eventually get Plutonium with Helium gas in it. So, from time to time, they have to replace the existing Plutonium with new Plutonium. Uranium does not have this problem since it has a long half life.... Also, Plutonium is very hard to work with. It is very dense, very hard, and very toxic (in addition to being radioactive).

[KarlMarx]

A few references

Nuclear 101: How Nuclear Bombs Work Part 1/2


https://www.youtube.com/watch?v=zVhQOhxb1Mc

Nuclear 101: How Nuclear Bombs Work Part 2/2


https://www.youtube.com/watch?v=MnW7DxsJth0

Plutonium - Periodic Table of Videos



https://www.youtube.com/watch?v=XLufmakbiU0

Trinity and Beyond - An *EXCELLENT* Documentary on the nuclear bomb narrated by William Shatner


https://www.youtube.com/watch?v=Hf6n0MsMBHs

[Little-Acorn]

I was wrong about a few things.

One of the first designs for a plutonium bomb was a slug gun. In theory it would have worked if pure enough plutonium were available. Just in case, the scientists started also planning an implosion bomb. Then when they found impurities in their plutonium, they realized the slug gun wouldn't work, though they were confident it would work with uranium. The plutonium slug guns were code-named "Thin Man" due to their shape, while the implosion bomb which was large and round, was code-named "Fat Man".

Even if they had pure enough plutonium, the plutonium slug guns would have been very long, too long to fit in the bomb bay of any existing or planned-for airplane. The uranium slug guns (code-named "Little Boy") were shorter, and would fit in a British Avro Lancaster or American Boeing B-29 Superfortress.

The hollow plutonium sphere at the center of an implosion bomb, was also an earlier design, but was very tricky to compress evenly. So they finally went with a smaller, solid sphere of plutonium and other metals, the size of a baseball. They relied on the high explosives around it to compress it down smaller than a golf ball, and that worked. The Trinity test in New Mexico, and the bomb dropped on Nagasaki, had that small solid sphere of plutonium. The small sphere tended to get warm when sitting inertly, but wouldn't go bang until it was highly compressed.

[Little-Acorn]

A picture from 1944, showing plutonium slug gun ("Thin Man") cases, soon discarded when impurities were found in the plutonium that make slug guns unworkable. In the background are several implosion ("Fat Man") cases.

https://upload.wikimedia.org/wikipedia/commons/c/ce/Thin_Man_plutonium_gun_bomb_casings.jpg