Ask any question you want about Physics

a reply to: Bedlam

Oh, the 65, the 48 or the 33?

a reply to: pfishy

The w-48 comes to mind. It was the sort of design that was eliminated due to a number of problems. But it's simple.

a reply to: Bedlam

I always liked the artillery round devices. They are close to pushing the limits of being able to attain a critical mass, from what I understand. At least for Plutonium or Uranium. Californium, on the other hand, whew. Anyone order nuclear bullets?

Could quantum tunneling be exploited to allow for nuclear fusion with little power input, yielding a great amount of output?

originally posted by: IAmTheRumble
Could quantum tunneling be exploited to allow for nuclear fusion with little power input, yielding a great amount of output?

Can't think of any way. A particle tunnel lung through something would be the exact opposite of why you want.

a reply to: dragonridr

Unless you could somehow stop the tunneling particle directly in the nucleus of the particle you are trying to cause it to fuse with. But quantum tunneling doesn't follow directions very well, I don't think.

a reply to: pfishy

If we can replicate tunneling, maybe it can be done. But I don't think we know how to do that.

originally posted by: IAmTheRumble
Could quantum tunneling be exploited to allow for nuclear fusion with little power input, yielding a great amount of output?

I'm not sure I understand the question, maybe you can clarify. Quantum tunneling refers to tunneling past some kind of barrier. What was the barrier you had in mind?

In the Oklo natural nuclear reactor, the average length of neutron travel through solid rock was estimated to be 2/3 meter, which provides one of the conditions for a natural nuclear reactor:

The Workings of an Ancient Nuclear Reactor

the size of the uranium deposit should exceed the average length that fission-inducing neutrons travel, about two thirds of a meter. This requirement helps to ensure that the neutrons given off by one fissioning nucleus are absorbed by another before escaping from the uranium vein.

Scientists studying the phenomenon surmised that the natural reactor operated in cycles. When the temperature reached a certain level the groundwater boiled away and the reaction stopped. When the reaction stopped it started cooling and eventually the groundwater flowed back in, and allowed the reaction to start again.

The reason for this is what dragonridr said: tunneling is the opposite of what you want. Tunneling allows the particles to go further, but to get the natural nuclear reaction to proceed, the opposite was needed; groundwater was needed to slow down the neutrons.

a reply to: Arbitrageur

I was hoping the tunneling concept could somehow be used to allow for fusion, with a lower amount of energy. Similar to "cold fusion" but in principle, it would be like the sun. Helping the particles pass the coulomb barrier, to form a larger nucleus and thus, fusion occurs releasing tons of energy.

Hope that makes sense.

a reply to: IAmTheRumble
Thanks for the clarification, so you're talking about the coulomb barrier. Sorry I misread your original question, but now I understand.

You'd need something like 10,000,000,000 degrees for fusion to occur without quantum tunneling, but it occurs at much lower temperatures such as those found in the sun's core (though they are still very high temperatures to us) because of tunneling, as explained here:

Overcoming the Coulomb Barrier

So, quantum tunneling is already taking place in fusion reactions in the sun's core which is "only" 27,000,000 degrees, far lower than the ~10,000,000,000 degrees it would need without quantum tunneling.

There's enough information in that link to show what range of particle energies can overcome the coulomb barrier using quantum tunneling, but as you can see there is still a lower limit which would not seem to permit cold fusion, unless something else is going on besides quantum tunneling.

a reply to: Arbitrageur

Thanks, i'll have a go at the link.

What holds two of the same element together? Making, for example: a piece of paper. How is each individual atom held together to create such a large structure of the same thing? Specifically, what holds an atom to the left and an atom to the right together? If that makes sense!

a reply to: IAmTheRumble

It is basically chemical bonding, which comes in several forms,

-Ionic crystals form by elements wanting to creating a lower energy state. One will loose electrons and end up in a nice happy low energy state, and the other will accept those electrons. You then get a natural coulomb attraction of these two elements and thus you may form an ionic crystal.

-Others form macroscopic chemical bonds with each other by which outer electrons are shared by two elements (in effect, its not quite like that but at the basic level its the same principle as above, you make a stable electron configuration by having electrons shared than not. while these may only form small molecules, these molecules still have regions that have higher and lower electron densities, and thus you can get these molecules to stick together and form larger structures based on something like van der walls attraction or coulomb attraction.

- Something like a metal seems to grow in crystals in which the outer valence electrons are very weakly bound to the nucleus and may jump between neighbouring atoms, this configuration of de-localised electrons allows electromagnetic attraction between each atom of the metal. it can be considered a single crystal molecule theoretically


The shape of a solid or a molecule is defined by the minimum stress and highest stability of the bonding. Example is water. One oxygen and two hydrogens.

The two hydrogens want to be as far away as possible from each other, so they are, they sit at either ends of the oxygen... but they are offset? why? Well the oxygen still has 4 more electrons in its outer shell and thus the most stable configuration is an equal repulsion between electrons. Thus you form a molecule that is roughly described by a triangle.


Very VERY basic, someone else should chime in, but thats the general gist of it

originally posted by: IAmTheRumble
What holds two of the same element together? Making, for example: a piece of paper.

Eros gave an excellent answer of how this can happen in metals.

With paper two of the same element aren't joined together, it's made of cellulose composed of strings of sugar molecules maybe thousands of molecules long depending on the type of cellulose. Each molecule has 6 carbon, 10 hydrogen and 5 oxygen joined together in a specific way. It's an amazing natural substance with long molecular chains that allow trees to grow to the amazing heights they do.

How is each individual atom held together to create such a large structure of the same thing? Specifically, what holds an atom to the left and an atom to the right together? If that makes sense!

As Eros said it's called a chemical bond which is an expression for a specific type of electromagnetic interaction, one of the four fundamental interactions, so it's the positive and negative charges in atoms interacting in certain ways which create chemical bonds. Our early ideas of electric attraction/repulsion couldn't explain what was going on very well but it made a lot more sense after we discovered quantum mechanics.

The interesting part of this story to me is how our observations led to grouping of certain elements in the "periodic table" based on their properties including their chemical bonding properties, before we understood the reasons why they should be grouped that way.

originally posted by: pfishy
a reply to: Bedlam

I always liked the artillery round devices. They are close to pushing the limits of being able to attain a critical mass, from what I understand. At least for Plutonium or Uranium. Californium, on the other hand, whew. Anyone order nuclear bullets?

miniaturized nukes with uranium and plutonium require additional neutron sources be diffused through the pit material. typically tritium which has to be replaced every 12 years or so due to tritium's halflife.

originally posted by: pfishy
a reply to: dragonridr

Luckily for all of us, certain components and fuels are extremely difficult to obtain, and require a very high level of precision to assemble properly.

you think so?

harpers.org...

unfortunately not.

if that stuff in there is true a high school student figured out a way to do nuclear enrichment without centrifuges and nation state level or even corporate level infrastructure. slow neutron bombardment.

originally posted by: stormbringer1701
you think so?

harpers.org...

unfortunately not.

if that stuff in there is true a high school student figured out a way to do nuclear enrichment without centrifuges and nation state level or even corporate level infrastructure. slow neutron bombardment.

I read that story. The kid bought:

-100 smoke detectors for the americium-241
-2000 lantern mantles for Thorium-232
-An antique clock which happened to have a vial of radium-226 paint in it, either left there by the clock painter by accident, or so the clock owner could re-paint the dial as needed.

He purified the radium which was dangerous to him. He had a little luck finding that vial of radium paint but the story doesn't say how big it was, it didn't have to be very big to touch up the clock face. Anyway I'm not sure how much luck you'd have trying to get more radium paint. You can still buy lantern mantles and smoke detectors but nothing in that story gives me any concerns that people are going to make bombs out of those.

He mixed his radioactive stuff together and got some reaction but I don't think we were ever in any danger of him making any kind of bomb. The biggest danger in the whole thing was of him increasing his chances of getting cancer or some other negative effect from the materials he worked with. It seems like he had very little idea about safety and otherwise only had a vague idea of what he was doing.

Everything he had was disposed of in a low-level waste site so apparently he never got very high concentrations of anything. He spent a couple thousand on his materials but taxpayers had to spend $60,000 to clean up his mess so I'm not impressed.

ah but neutron activity increased over time in his home brew. his little slow neutron gun worked.

a reply to: stormbringer1701

He never created fissile material. But that's not to say it's impossible. Also, to continue in that experiment to the point of actually obtaining enough material to create a bomb with would have both been extremely costly, and probably killed him before completion.
I wouldn't exactly call that easy.

originally posted by: pfishy
a reply to: stormbringer1701

He never created fissile material. But that's not to say it's impossible. Also, to continue in that experiment to the point of actually obtaining enough material to create a bomb with would have both been extremely costly, and probably killed him before completion.
I wouldn't exactly call that easy.

just because he didn't have a clue about safety precautions does not mean his neutron gun didn't work as he had hoped. the radioactivity level increased over time. what he was doing was slowing the neutrons down enough from a already nearly slow enough source to get the regular "safe" isotopes he had to take on extra neutrons. that's what he thought he was doing and the rising radioactivity seems to indicate that as well plus (and i could be completely wrong) I think i remember reading papers or articles on enrichment by slow neutron exposure. not sure if i remember right or not.