nuclear fission

[bwanaaa]

How did physicists actualy come up with the idea of nuclear fission.? Einstein was doing relativiyty stuff. Nothing in that suggests a mechanism for achieving fission as a means for converting matter to energy. Furthermore, there is no natural example in our daily lives that would lead to the idea that a 'neutron cascade' could promote fission. who was doing what? and who actually came up with the idea that an a=bomb was possible?

 

[RossGr]

Einstein's work in relativity is completly seperate from the work that was done in Quantum Mechanics in the first half of the 20th century. Einstein did get the ball rolling with his Nobel Prize winning paper on the Photoelectic effect. While that was pretty much the birth of QM, it was concieved some years earlier by Plank. But it was not till after A.E.s paper (Photoelectric Effect) that QM really got started. Many Physicists contributed to this work. Born, Heisenberg, Schrodinger, Chadwick, Dirac, Pauli to name a few.

While most of this work was being done, A.E. was working on General Relativity and attempting to find the Theory which unified GR and QM. He was unsucessfull, and we continue to search for the GUT.

 

[bwanaaa]

You must be thinking in a higher dimension because your reply is a nonsequitur to my question of 'who specifically thought of building an a bomb using a neutron cascade'.. .Babbling the names of physicists is reassurring but it is their work that interests me. What did Fermi do his thesis in?

 

[capybara]

deleted

 

[KenGr]

This is where physics gets much more involved that E=MC2. Once Einstein established that mass could be converted to (huge amounts of) energy, the question was how to do it. Studies of atomic structure lead to two conclusions. First that heavy atoms contained more mass than would exist in two lighter elements with the same quantities of protons and neutrons. Therefore, if the heavy atoms could be split into two or more lighter atoms, there would be a net release of energy. (This is related to a quantity called binding energy which is a continuous curve from light to heavy elements. A graph of binding energy vs atomic weight lets you see immediately that both fission of heavy elements and fusion of light elements results in a net release of energy.) Second, studies of radioactive elements had determined that these decayed due to instability in the nuclear structure. Also, the half life varied depending on how unstable the elements were. Therefore, if an unstable form could be created that decayed by fission, not just kicking out a single particle or ray, energy could be produced.

It was really the application of relativity to huge amounts of work on atomic structure by Curie, Bohr and many others that allowed Fermi (and others) to conclude that controlled and uncontrolled fission was possible.

 

[RossGr]

I am puzzled about what you want. If the list of names that I gave you is of no interest, then what is of interest? Perhaps you could do a bit of reseach on your own, I would recomend a web search on Chadwick, He was head of the group that first found a neutron experimentally, and also was a part of the group you created and controlled the first sustained chain reaction. Much of the history of this development is in the men who did the work, read their words or at least works about them and you will have the story of the devleopment of nuclear power.

You tell me, what did Fermi do his thesis on, I do not know.

 

[unclebabar]

If I had to guess I would say the Curies or maybe on a more basic level, Mendelev's periodic table in conjunction with Dalton's (?) theory on the structure of the atom. If you look at the periodic table all elements get less 'dense' in terms of energy units until you get to iron, whereafter they become more dense. Now I say the Curies because they are known for their study of radioactivity. Afterwards any astute scientist making an empirical observations could see that as a heavier element undergoes alpha decay it becomes a lighter element and releases energy. It is perhaps a short walk to imagine the energy available when an atom is forcibly split in two.

Now I'm just an old fart with a Computer Science degree, not a physicist or anything close, so don't take the above as gospel.

 

[zhena]

i think what he is asking is what was the reason that created the initial "push" so to say for scientists to look at fission and fusion.

as far as i know a lot of it had to do with the invention of x-rays or more to the point the discovery of radio active material.
once radio active elements were studied fusion and fission was the natural progression of logical uses for such material.

 

[capybara]

well, according to my uncle who worked on the Manhattan Project, Fermi was the
man who made it happen. But i dont think he claimed credit for the original "idea".
Several designes were tried before the successful geometry was achieved.

 

[blahblah99]

There's this book called "The Making of the Atomic Bomb" and its about 1000 pages in length. It describes the history of the atomic bomb and how it came about.

Its not one person that came up with the idea. Its a culmination of ideas a few people, and one thought lead to another. Szilard, Curie, Bohr, Einstein, Fermi, and Oppenheimer were a few of the people.

 

[woolmilk]

There is natural fission of radioactive materials. Of course not in our daily lives. Henri Becquerel discovered radioactivity in 1896. The chemist Otto Hahn had been working a lot with radioactive materials and discribed the natural fission of Uran first in 1939. The experiment showed a loss of mass, which could be explained by Einsteins famous equotion.

Einstein published his first paper on special relativity in 1905. The formular e=mc2 simply pops out of the equotions. Of course no one did believe him or understand what his paper did contain or if matter can be transformed anyhow into energy. It took until 1939 when Einstein was informed by the physicians Szilard an Wigner about the possible use in military using a chain reaction of Hahns discovery. His reaction: "I never thought of that". But he used his grown popularity to promote further research signing a letter to the american goverment.

 

[SinfulWeeper]

I dunno know who came up with the idea of how to build the bomb. What I do know is this, when all the atoms split. The entire chain reaction is done in less than 20 billionths (or was is trillionths?) of a second. Done... nada... no more...
The explosion you see is the 'waste' of that fraction of a second.

The person who figures out to keep that waste contained and stored will be shot and killed by the oil companies because of the threat it poses to them. Think of that one for a while.

 

[Walleye]

um, nuclear power inside a power plant and nuclear power inside a bomb are completely different.

a bomb works on making uranium go above critical mass. that means compressing it.

one way to compress it was to slam it together. Little Boy was an example of this. it was a piece of Uranium at 1 end of a cannon barrel, and another piece of uranium, shot from the other end of the barrel at the first piece of uranium.

Later, (by a few days) we developed a better method, a sphere implosion technique. you surround a sphere of uranium with plastique, and detonate that, compressing the inner uranium. that's the other way to reach supercritical mass.

when that happens, it becomes extremely unstable, and releases a huge amount of energy in a split second, blowing apart the casing, and sending out a shockwave, along with some radiation, destroying stuff in it's path.

that's the simple version of a very complex process.



Oh, and in the event of a nuclear blast, hope your bomb shelter is directly underneath the blast, and shielded from radiation, cause that way the buildings overhead wont come down and wreck your shelter.


Oh, and the making of the Atomic Bomb by Richard Rhodes is a very good book. I also Reccommend Dark Sun, the making of the Hydrogen Bomb. They are really very historically informative.

 

[KenGr]

Originally posted by: SinfulWeeper
I dunno know who came up with the idea of how to build the bomb. What I do know is this, when all the atoms split. The entire chain reaction is done in less than 20 billionths (or was is trillionths?) of a second. Done... nada... no more...
The explosion you see is the 'waste' of that fraction of a second.

The person who figures out to keep that waste contained and stored will be shot and killed by the oil companies because of the threat it poses to them. Think of that one for a while.

Fission is fission, whether it's a reactor or a bomb. The difference in geometry just means that the reactor, in the worst case, can slightly supercritical (this is how power is increased - with a small supercritical transient) while the bomb can go massively supercritical. If the fissile material is the same, the reaction is the same.

Actually, the concept of using a "bomb" for power production was fairly well developed some years ago. Essentially you would develop a large underground compartment and set off, at regular intervals, small bomb blasts. This would create high pressure and temperature which could be tapped at a steady rate for power production. There's no reason it can't work but it holds no real economic advantage over power reactors. Also, it's completely unacceptable from a proliferation viewpoint, so don't expect to see this one proposed.

 

[f95toli]

Leo Szilard came up with the idea of using a a chain reaction, but he did not have any idea about what kind of mechanism to use (he came up with the idea before the neutron was discovered by Chadwick) but he did get the patent (in England).
A few years later Lisa Meitner and Otto Frisch showed that certain reactions that occur in nature can be explained by assuming that an incoming netutron hits the nucleus and splits it into two pieces, the motivation for this work were some experiments by Otto Hahn.

Einstein was never really involved in the construction of the bomb, his main contribution was signíng a letter (written by Szilard) to FDR asking him to fund the bomb-reserach.
The most important people in the Manhattan project were probably Oppenheimer (head of research), Fermi, Teller, Bethe, von Neuman, Niedermayer (came up with the idea of an implosion), Seaborg and Kistakowsky (explosives expert). Szilard was never really involved in the actual research and Meitner was stuck in Europe. Bohr (and his son) was also helping them with some problems.

Almost all the greatest physicists in the world were working on the Manhattan project, the expceptions beeing Heisenberg who was working on the German bomb and the Russians.

 

[themadmonk]

Originally posted by: Walleye
um, nuclear power inside a power plant and nuclear power inside a bomb are completely different.

a bomb works on making uranium go above critical mass. that means compressing it.

one way to compress it was to slam it together. Little Boy was an example of this. it was a piece of Uranium at 1 end of a cannon barrel, and another piece of uranium, shot from the other end of the barrel at the first piece of uranium.

Later, (by a few days) we developed a better method, a sphere implosion technique. you surround a sphere of uranium with plastique, and detonate that, compressing the inner uranium. that's the other way to reach supercritical mass.

when that happens, it becomes extremely unstable, and releases a huge amount of energy in a split second, blowing apart the casing, and sending out a shockwave, along with some radiation, destroying stuff in it's path.

Critical mass is the mass of any radioactive substance that the amount of nuetrons escaping from the surface is less than the amount of nuetrons generated by fission inside the mass in question. The reason they split it, is because once it reaches critical mass, you will have multiple sustainable fissions. It has nothing to do with compression. And what they do, is to split a sphere, because a sphere offers the best ratio of surface area to volume, then using a small explosion, cause the two parts of the sphere to come together and fuse long enough to achieve that sustainable fission.

 

[bwanaaa]

But the idea of using neutrons is peculiar. For a much longer time, people knew about alpha particles (2n+2p) and the much more agile beta particles (1e). Why werent these actors candidates for triggerring a cascade? After all, alpha particles are more massive and larger than a neutron and therefore more likely to produce a 'fruitful'collison. How is it known anyway that it is a neutron cascade that leads to the splitting of an atom? not a proton cascade?

I can see the concept of a chain reaction lead to the birth of an idea of the atom bomb. It's interesting that they thought the event would be so rapid. rather like the idea of gunpowder that fizzles when its not contained, but put it into a confined space and you have an explosion. I can further see how this concept of chain reaction can lead to the prediction of unlikely side effects-like the consumption of the entire atmosphere that worried them before the first test.

I wonder much radioactivity was released by all the nuclear tests over the years?

 

[f95toli]

When Szilard came up with the idea of a chain reaction he had one problem: There was no suitable particle. When Chadwick discovered the neutron (explaining the difference between isotopes) the problem was solved. The neutron does not carry any charge and can therefore penetrate the nucleus. A charged particle like the alpha-particile of a proton is repelled by the nucleus since the nuceleus consists of protons and neutrons. A slow neutron can reach the nucleus and make it unstable which splits it into two.

 

[themadmonk]

I wonder much radioactivity was released by all the nuclear tests over the years?

I am more worried about the ones in the coming years.

 

[silverpig]

I think there have been something like 2700 tests so far in the history of the world... That's a lot.

 

[bwanaaa]

AHA! thank you f59toli. An interesting problem that parallels the present difficulty in maintaining a sustainable fusion rxn. But that begs the question of why a neutron add to a nucleus makes it unstable? There are for example stable isotopes that result from neutron bombardment. Was it dum luck that neutrons thrown into U238 result in fission? Probably not, the observation of radioactive decay had been known for a while and certainly catalogued by the various elements. The use of neutrons was an educated guess? or was it because it was the only other ingredient in their kitchen? After all, why not try injecting neutrons into a plasma core? might that not facilitate (or 'catalyze' to use a chemical term) fusion. Would an intermediate inherently unstable compound be more likely to progress to fusion than trying to squeeze 2 hydrogen atoms together? Think of it as lowering the activation energy. That might make the present day "magnetic bottle" approach to fusion not only more easily attainable, buut also more controllable.

As for the2700 tests done so far, I wonder about the effect of of the long lived by products. Would it not be ironic that now, as we approach the dawn of the stem cell era (stem cell age?) where we can renew our body parts indefinitely, that the only impediment might be the toxic soup we live in?

 

[Walleye]

most of those 2700 tests were done underground. a few of them were done in space. a H-bomb in space looks cooler than it does on land. that's for sure.

anyway, the radioactivity of all the tests, minus the ones underground, has pretty much gone down to livable levels. the problem with the ones underground is that the radiation is seeping through the ground, into open air. It'll take probably another 500 or so years before the radiation in those caverns is at a livable level (for short periods), probably 2000 years for long periods of exposure.

in the coming years, we may perfect the neutron bomb, and have no need of nukes at all.

(the neutron bomb is a bomb specifically targeted towards living organisms. you detonate it, it runs it's course, and 5 minutes later you're set to occupy the enemy city, with all their buildings still intact to house your command center, and such. it releases no long lasting radiation. but as it is now, we have fusion bombs which cut the life of the contamination from 2K years to 5 or so years, on the average sized bomb.

 

[RossGr]

in the coming years, we may perfect the neutron bomb, and have no need of nukes at all.

read this The neutron bomb is not a future device, it is real and has been for 30+ years.

 

[Walleye]

oh. i didnt kinow thaty they had been finished. i had thought they were stikll in the testing phase. It seems as things near the end of their development, they get talked about less and less. kinda like the bladeess propulsion system the soviets were working on. Yeas, the propulsion system on trhe Red October in that cool movie/book, was a real system being developed. but it seems as though it is never talked about anymore.

so whens the next asteroid set to hit the planet? i havent heard anything about that.

 

[SinfulWeeper]

Originally posted by: KenGr

Originally posted by: SinfulWeeper
I dunno know who came up with the idea of how to build the bomb. What I do know is this, when all the atoms split. The entire chain reaction is done in less than 20 billionths (or was is trillionths?) of a second. Done... nada... no more...
The explosion you see is the 'waste' of that fraction of a second.

The person who figures out to keep that waste contained and stored will be shot and killed by the oil companies because of the threat it poses to them. Think of that one for a while.

Fission is fission, whether it's a reactor or a bomb. The difference in geometry just means that the reactor, in the worst case, can slightly supercritical (this is how power is increased - with a small supercritical transient) while the bomb can go massively supercritical. If the fissile material is the same, the reaction is the same.

Actually, the concept of using a "bomb" for power production was fairly well developed some years ago. Essentially you would develop a large underground compartment and set off, at regular intervals, small bomb blasts. This would create high pressure and temperature which could be tapped at a steady rate for power production. There's no reason it can't work but it holds no real economic advantage over power reactors. Also, it's completely unacceptable from a proliferation viewpoint, so don't expect to see this one proposed.

Yes, blasting a bomb has been in use for power production for a long time.

However you missed my point. The 'waste' or explosion is the byproduct of wasted energy. The most common type waste is in the form of your every day autombile engine. An explosion is controlled in the cylinder and contained in there.
What I was suggesting on why a person would be assainated by the oil companies is really simple. Either it be nuclear or conventional, would be to make a form of power production that exceeds 75 percent efficency and done cheaply. When the atoms split or join in nuclear weapons, and let off that energy. It is so overwhelming that current techology can not let it be contained and harnessed in its pure form. Sure there are nuclear power plants. But that is a prime example of inefficiency. It does not use the power from the 'core', instead it makes steam to turn a turbine.