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splitting the atom


the guy
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The answer can be very short, or very long, as samtheflash82 already said.

 

The famous E=mc^2 formula is the one you need to know here.

 

E = energy

m = mass

c = speed of light

 

So, this energy is indeed "stored". It's stored in the form of mass. When an atom splits, the products are a bit lighter than the original, and mass in fact disappears, and (lots of) energy is created.

 

I probably use words which are too simplistic, but something tells me that you're not interested (yet) in the very long answer.

I also advise you to click around a bit on wikipedia.

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So, this energy is indeed "stored". It's stored in the form of mass. When an atom splits, the products are a bit lighter than the original, and mass in fact disappears, and (lots of) energy is created.

 

Another way of viewing this is that the products are more tightly bound than the parent. In order to form a more tightly bound system, you have to give up energy, and that's why the mass decreases.

 

And the energy released is essentially all due to the decrease in the electrostatic force.

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I always thought that it was the 'Strong force' that held the atom together. How does the electrostatic force play into it?

 

The strong force is saturable, the EM isn't. The nucleus is full of closely packed positively charged protons.

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the most stable atoms nuclearly, with the most binding force, are iron-56 and nickel-58. atoms with lower masses often fuse or such to try to get to about 56. atoms with higher masses are often unstable and split up to get down to around 56. Helium is pretty stable also. Atoms that have too few or too many neutrons are also unstable (between 1 and 1.5 is the best ration for protons/neutrons.)

 

This is because, as somebody mentioned, the protons are all ppositively charged and repel each other, but at close enough distance gravity between the protons and neutrons is higher than the repulsive forse... in large atoms this force comes into play...

 

here's a graph of the binding energy of the elements

 

that also explains why iron is the most abundant element in the earth (earth's core is molten/solid iron) and many stars ... the center of most stars is iron (although our sun works exclusively on [math]^{2}_{1}[/math]H + [math]^{2}_{1}[/math]H > [math]^{4}_{2}[/math]He)

Edited by coke
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Er...wait, what's saturating the strong force? I'm a little confused.

 

The strong force has a finite range, so the nucleons inly interact with a finite number of particles; essentially only the nearest-neighbors are attracted. So a proton or neutron on one side of a large nucleus does not attract any of the particles on the other side — adding more does not increase the attraction (unlike gravity or electrostatics, where adding more mass/charge does increase the force) Splitting it in half changes this very little. But you've dropped the electrostatic repulsion of all the protons, which is the product of the two charges, i.e. it's a quadratic term.

 

The energy it takes to bring a ~40e and ~50e nucleus to ~ 10^-14m apart is a few hundred MeV. Fission of U-235 releases ~200 MeV.


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This is because, as somebody mentioned, the protons are all ppositively charged and repel each other, but at close enough distance gravity between the protons and neutrons is higher than the repulsive forse... in large atoms this force comes into play...

 

Strong force. Not gravity.


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how do they actually split it? thats whats puzzeled me, do they slam a particle into a uranium atom to split it?

 

Excitation of a nucleus deforms it — it behaves like a liquid drop. When the nucleus deforms, you can get a situation where the nuclear force is has decreased (in the "neck" of a dumbbell-shaped vibration) to the point where the electrostatic repulsion tears it apart. For some nuclei, just absorbing a neutron is sufficient to give this excitation, while for others the neutron must have some kinetic energy.

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Strong force. Not gravity.

 

right, thanks...

 

When I wrote that, I thought there were only two forces- electromagnetic and gravity.

 

But of course there are two more- strong force, and another one, weak force or something?

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right, thanks...

 

When I wrote that, I thought there were only two forces- electromagnetic and gravity.

 

But of course there are two more- strong force, and another one, weak force or something?

 

That's right. The strong force acts between nucleons (protons and neutrons) but not leptons (e.g. electrons). The weak force acts between leptons and quarks, but has a very short range.

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