A little confusion about nuclear fission discovery and theory

[DAgent]

So this has me scratching my head a bit and I'm looking for a clearer answer, if possible, please.

I've been reading the splitting of the atom was first performed in 1932, however, the theory of splitting the atom wasn't done until 1938.

Now I'm not thinking time travel played any role in this, but trying to read up and sort out the timeline on how it could be discovered before the theory was crafted is leaving me with a splitting headache, pun intended. It's also been a busy day in general and I'm worn out for other reasons, so I've effectively gone word-blind right now.

I'm assuming there was some earlier versions of the theory before the atom was split, and that the theory was revised until they felt that got it right. Is this the way it happened or am I way off? Which is more like to be true to be utterly frank.

Thanks.

 

[BAYLOR]

So this has me scratching my head a bit and I'm looking for a clearer answer, if possible, please.

I've been reading the splitting of the atom was first performed in 1932, however, the theory of splitting the atom wasn't done until 1938.

Now I'm not thinking time travel played any role in this, but trying to read up and sort out the timeline on how it could be discovered before the theory was crafted is leaving me with a splitting headache, pun intended. It's also been a busy day in general and I'm worn out for other reasons, so I've effectively gone word-blind right now.

I'm assuming there was some earlier versions of the theory before the atom was split, and that the theory was revised until they felt that got it right. Is this the way it happened or am I way off? Which is more like to be true to be utterly frank.

Thanks.

Im no physicist , but a common sense standpoint , before atom splitting was possible and happened , certain key steps and discoveries to have taken place prior.

 

[Venusian Broon]

Cockcraft and Walton 'split the atom' in 1932 by bombarding lithium with a proton beam and showing that when the proton hit the lithium nucleus (and was absorbed via Quantum tunnelling) the nucleus would break apart into two alpha particles.

Hahn and Strassmann in 1938 discovered nuclear fission by bombarding uranium with slow neutrons and finding some barium.

The difference between the two experiments is that Cockcraft and Walton's experiment is not fission - it was not as a result of initiating an internal radioactive decay process. (Just smashing things together!)

So I guess what you read is saying: that a theory of nuclear fission was only developed in 1938 to account for Hahn and Strassman's work.

Probably unhelpfully, 'splitting the atom' could be applied to both, and probably was in popular culture.

Does that help?

 

[Swank]

Apparently splitting a lithium 7 nucleus via alpha wave bombardment was not a "nuclear fission reaction" - the thing discovered in 1938 that releases gobs of energy.

 

[Foxbat]

Nuclear Fission can also occur naturally

Meet Oklo, the Earth’s Two-billion-year-old only Known Natural Nuclear Reactor

Physicist Francis Perrin sat at a nuclearfuel-processing plant down in the south of France, thinking to himself: “This cannot be possible.” It was 1972.

www.iaea.org

 

[DAgent]

Cockcraft and Walton 'split the atom' in 1932 by bombarding lithium with a proton beam and showing that when the proton hit the lithium nucleus (and was absorbed via Quantum tunnelling) the nucleus would break apart into two alpha particles.

Hahn and Strassmann in 1938 discovered nuclear fission by bombarding uranium with slow neutrons and finding some barium.

The difference between the two experiments is that Cockcraft and Walton's experiment is not fission - it was not as a result of initiating an internal radioactive decay process. (Just smashing things together!)

So I guess what you read is saying: that a theory of nuclear fission was only developed in 1938 to account for Hahn and Strassman's work.

Probably unhelpfully, 'splitting the atom' could be applied to both, and probably was in popular culture.

Does that help?

I think it clears it up a fair bit. It's just that when you look up who split the atom first it's Cockcraft and Walton who get the credit for it, and Hahn and Strassman get the credit for discovering nuclear fission, but when I look up whether nuclear fission and splitting the atom is the same thing, everywhere on line says yes.

And then I end up going down a rabbit hole that gives me that headache. It just seems there's too many contradictions flying around out there :/

 

[Robert Zwilling]

Just keep reading, history is usually a partial explanation of what happened and so it takes several attempts to put it all together, which you have to do yourself. The internet is quite helpful once you become adept at sorting out information as to good, bad, or indifferent. In the old days you had to go to a library, or more than one library, and look through/read a lot of books.

 

[Swank]

I think it clears it up a fair bit. It's just that when you look up who split the atom first it's Cockcraft and Walton who get the credit for it, and Hahn and Strassman get the credit for discovering nuclear fission, but when I look up whether nuclear fission and splitting the atom is the same thing, everywhere on line says yes.

And then I end up going down a rabbit hole that gives me that headache. It just seems there's too many contradictions flying around out there :/

Nuclear fission is splitting the atom, so there is no contradiction.

 

[Foxbat]

With @Venusian Broon example (who will no doubt correct me if I get it wrong)

If I recall correctly, Lithium has 3 protons and 4 neutrons. So can’t become 2 Alpha particles (each containing 2 protons and 2 neutrons…same as a Helium nucleus).
The neutron hitting the Lithium nucleus becomes a proton and emits a beta particle (and probably a gamma photon but I’d have to look that bit up). This gives you the 4 protons and 4 neutrons for the two alpha particles but before they are emitted, it is no longer Lithium. The fourth proton changes it into an unstable isotope of Beryllium.

So, as said previously, no contradiction, it is not fission because it did not split as per the definition. The Lithium nucleus had to absorb a neutron (and effectively change) before emitting the alpha particles. Put simply, a nucleus undergoing fission does not have to change into a different element first for this to occur. The Lithium did have to change. If you split Uranium 235 with a proton, you split Uranium 235. If you hit Lithium with a proton, you change it into Beryllium, which then, (through radioactive decay) emits 2 Alpha particles. Two different processes.

 

[hitmouse]

Some really good responses here. If you ditch the imprecise lay term “splitting the atom” it becomes more clear.

 

[Dave]

I had realised before that the term "splitting the atom" could be so widely interpreted, but this all makes sense really. It is similar to the "space race," which had begun long before any finish line for it was set, and did everyone involved sign up to that end goal? They're both attempts to capture the public's attention for science projects in order to win future investment. It is a journalistic invention rather than something with a scientific definition.

 

[Venusian Broon]

With @Venusian Broon example (who will no doubt correct me if I get it wrong)

If I recall correctly, Lithium has 3 protons and 4 neutrons. So can’t become 2 Alpha particles (each containing 2 protons and 2 neutrons…same as a Helium nucleus).
The neutron hitting the Lithium nucleus becomes a proton and emits a beta particle (and probably a gamma photon but I’d have to look that bit up). This gives you the 4 protons and 4 neutrons for the two alpha particles but before they are emitted, it is no longer Lithium. The fourth proton changes it into an unstable isotope of Beryllium.

Sorry @Foxbat

The Cockcroft experiment used a proton beam not a neutron one. From memory the neutron had only just been discovered the same year as the lithium-proton experiment by Chadwick.

Thus no need for a beta decay to get the result.

Alpha and beta particles were well known at the time, so the fact that Beryllium-8 emitted an alpha particle and left an alpha particle was not seen as remarkably new, I think. In fact the experiment was designed to observe alpha particles to show that it had been successful.

I believe the experiment was carried out to show that, using a relatively low energy proton beam, quantum tunnelling was shown to be possible. (I may be wrong, but that was my quick summarisation ) Cockcraft and Walton got the Nobel prize in 1951 for their 'pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles.'

Fission is the breakdown of nuclei into smaller ones through natural radioactive processes - i.e. alpha and beta decay - where, as part of the process, a small portion of the total mass of the original atom is converted into (lots of) energy. Typically we think of very heavy nuclei being involved.

Beryllium-8 emitting an alpha particle is, in fact, a natural process - the isotope can be produced in nature* - it just is incredibly unstable and has a half-life of something like 10^-17 seconds. And so it looks like fission when I say it that way....but as the remnant nuclei was just an alpha particle, not a number of different daughter elements, and at the time they were not aware of the concept of fission as I've stated above, they did not see nor test for any 'fission ramifications'.

(Actually, Be-8 is slightly more massive than two helium atoms, so I assume there is some conversion of mass into energy in the reaction, but I don't know if they were able to measure the mass of Be-8 at the time to the required accuracy.)


=======================

* It's one of the reasons the universe did not produce heavy elements and required stars for heavy elements to be as abundant as they are now, as Be-8 would breakdown faster than it was possible for another helium nuclei to collide with it and go on to produce carbon in the very early universe.

 

[Foxbat]

The Cockcroft experiment used a proton beam not a neutron one. From memory the neutron had only just been discovered the same year as the lithium-proton experiment by Chadwick.

Scotoma.
Because we were discussing fission, I hooked on to neutrons.
We see what we want to see.

 

[Venusian Broon]

In a nicely synchronistic turn of events, (strangely synchronistic if you ask me, I think the cosmic joker is playing about with us), Sabine Hossenfelder just published this vid on a potential anomaly with Be-8 decay in a set up very much like the experiments we were musing over above.

Turns out even working physicists are still a bit confused with what's happening @DAgent . If you're confused, you are in good company

 

[Foxbat]

Quote from the video: If you torture the math long enough, it will confess to anything.
I love it

Another: still extremely confused but now with more expensive equipment