Do we understand the laws governing the energy configuration of the nucleas yet?

[sao123]

Ok so we know that electrons fill the shells to allow the atom to exist in its lowest energy (ground) state. We believe that protons and neutrons do also...

do we have any clue how this happens so far?
Do we have any clue as to the shape and size of the nuclear shells?



How does adding 3 neutrons to U 235 to make U 238, make it more stable and less useful for making a bomb? Also, does this theory explain why a certain isotope of an element follows a specific radioactive decay path and can we use it to predict other radiodecay paths?

 

[NucEm]

After you add the first neutron to U-235 you may want to step way way way back because you're about to be nuc'd.

 

[Fox5]

Eh, maybe gravity holds the atom together, and when there's more mass there's a strongest effect on the electrons! Pseudo-science rawks.

 

[KingofCamelot]

Originally posted by: Fox5
Eh, maybe gravity holds the atom together, and when there's more mass there's a strongest effect on the electrons! Pseudo-science rawks.

Actually it is the electrical force caused by the attraction of electrons and protons that holds the electrons to the atom.

 

[CycloWizard]

I'm pretty sure there are well-developed theories surrounding this, involving strong and weak forces. I can't remember really anything about them (even what the forces are called, for shame!), but I'm sure someone that can will stop by before too long.

 

[Calin]

More protons in the nucleus make it less stable. However, more neutrons in the nucleus stabilize it. Of all elements with the same number of protons, the izotopes with the biggest number of neutrons are the most stable.

 

[cquark]

Originally posted by: sao123
Ok so we know that electrons fill the shells to allow the atom to exist in its lowest energy (ground) state. We believe that protons and neutrons do also...

do we have any clue how this happens so far?
Do we have any clue as to the shape and size of the nuclear shells?

How does adding 3 neutrons to U 235 to make U 238, make it more stable and less useful for making a bomb? Also, does this theory explain why a certain isotope of an element follows a specific radioactive decay path and can we use it to predict other radiodecay paths?

Unfortunately, the nuclear shell model doesn't work nearly as well as the electron shell model. Nuclei are held together by a secondary effect of the strong nuclear force (the primary effect is binding quarks to form neutrons and protons.) The strong nuclear force is highly nonlinear, as unlike the electromagnetic force, which is transmitted through chargeless photons, the strong force is transmitted through gluons which do have "strong charge." In order to keep the nucleus stable, the strong nuclear force must resist the repulsive effect of the electromagnetic force on the protons.

Each nucleon (neutron or proton) added to the nucleus contributes to the binding nuclear force, but each proton added contributes to electromagnetic repulsion attempting to tear the nucleus apart. Elements later in the period table (which have higher Z=number of protons) require more neutrons to contribute to their strong binding force to maintain stability. You can find a graph of binding energy/nucleon at
http://cwx.prenhall.com/bookbind/pubboo...portfolio/text_images/CH19/FG19_06.JPG

While the strong force is stronger than the electromagnetic force, it has a very short range and the electromagnetic force has infinite range. Once the nucleus grows to a certain size, adding more neutrons doesn't increase the binding force sufficiently to maintain stability due to the short range of the strong force. Shell configurations help determine the size of the nucleus, as they reflect the Pauli Exclusion Principle preventing you from placing all of the nucleons as close together as would otherwise be possible. You can find a plot of the "belt of stability" (the region where you have enough neutrons to keep the nucleus stable) at
http://cwx.prenhall.com/bookbind/pubboo...portfolio/text_images/CH19/FG19_04.JPG

 

[DrPizza]

Related topics, and possible this topic are explained fairly well at www.particleadventure.org

edit: no, it doesn't go into as much detail as the OP's question needs. However, it's an excellent starting ground for anyone who even suspects gravity holds the particles together. (I'm hoping it was a joke)

 

[f95toli]

Just to answer the OP:

Yes, we understand it very well. It is extremely complicated but AFAIK it is possible to calculate just about any property of an isotope with almost arbitrary accuracy (using a computer).

 

[Zolty]

Originally posted by: NucEm
After you add the first neutron to U-235 you may want to step way way way back because you're about to be nuc'd.

only if there are a bunch more U-235's around

 

[iwantanewcomputer]

Originally posted by: cquark

Originally posted by: sao123
Ok so we know that electrons fill the shells to allow the atom to exist in its lowest energy (ground) state. We believe that protons and neutrons do also...

do we have any clue how this happens so far?
Do we have any clue as to the shape and size of the nuclear shells?

How does adding 3 neutrons to U 235 to make U 238, make it more stable and less useful for making a bomb? Also, does this theory explain why a certain isotope of an element follows a specific radioactive decay path and can we use it to predict other radiodecay paths?

Unfortunately, the nuclear shell model doesn't work nearly as well as the electron shell model. Nuclei are held together by a secondary effect of the strong nuclear force (the primary effect is binding quarks to form neutrons and protons.) The strong nuclear force is highly nonlinear, as unlike the electromagnetic force, which is transmitted through chargeless photons, the strong force is transmitted through gluons which do have "strong charge." In order to keep the nucleus stable, the strong nuclear force must resist the repulsive effect of the electromagnetic force on the protons.

Each nucleon (neutron or proton) added to the nucleus contributes to the binding nuclear force, but each proton added contributes to electromagnetic repulsion attempting to tear the nucleus apart. Elements later in the period table (which have higher Z=number of protons) require more neutrons to contribute to their strong binding force to maintain stability. You can find a graph of binding energy/nucleon at
http://cwx.prenhall.com/bookbind/pubboo...portfolio/text_images/CH19/FG19_06.JPG

While the strong force is stronger than the electromagnetic force, it has a very short range and the electromagnetic force has infinite range. Once the nucleus grows to a certain size, adding more neutrons doesn't increase the binding force sufficiently to maintain stability due to the short range of the strong force. Shell configurations help determine the size of the nucleus, as they reflect the Pauli Exclusion Principle preventing you from placing all of the nucleons as close together as would otherwise be possible. You can find a plot of the "belt of stability" (the region where you have enough neutrons to keep the nucleus stable) at
http://cwx.prenhall.com/bookbind/pubboo...portfolio/text_images/CH19/FG19_04.JPG

these graphs explain it all, just where the nuclear force (Strong/weak/both...i don't have a clue) holding it together overpowers the electromagnetic force of a bunch of + charges repelling each other

 

[cquark]

The strong force holds the nucleus (and the nucleons) together, while the weak force induces fundamental radioactive decays (n -> p + e + v(bar), etc.)

 

[sao123]

Interesting read Static Nuclear Structure and Atomic Physics

 

[MobiusPizza]

Originally posted by: Calin
More protons in the nucleus make it less stable. However, more neutrons in the nucleus stabilize it. Of all elements with the same number of protons, the izotopes with the biggest number of neutrons are the most stable.

Only partially correct. All nucleons, protons or neutrons wise, would bind together stronger if more nucleons are present. However, when coulomb effect come into place (the electrostatic forces) it offset the balance.

Since protons have charge, more of it inside a nucleus would mean more coulomb replusion. However if there's more neutrons to "glue" the nuclues together it would be more stable. BUT, too many neutrons are undesirable since if a neuclues have too many neutrons they tend to undergo beta decay to give protons. Hence potentially giving a unstable isotope.

A note is that even though some nucleus have alarmingly high numer of proton; But the neuclues does not blast off. It just decay by beta plus decay into a neutron. THE REASON for this instability is NOT because the nuclear binding force is too weak compared to coulombic replusion, as the nucles did not blast off. It's still sufficient to glue the atoms together. It is natural for binded protons and neutrons to decay into each other. This cannot be explained though. Nevertheless it is more rare to find beta plus decay isotopes simply because this structure stable (not blasting off) atom structure is harder to maintain than neutron rich cases

The most stable nucleus is Iron having an atomic number of 53?? If you plot a graph of binding energy against atomic number, you get anegatively skewed odd graph. It shoots up from hydrogen then levels off at iron, then drops graduately. The more binding energy there are, the more stable the nucleus.

Initally up to Iron the for stable isotopes ratio between no. of protons and neutrons is approx. 1:1. But for heavier elements the ratio is about 1:1.5 (More neutrons needed for coulomb offsetting)

 

[Fox5]

Originally posted by: KingofCamelot

Originally posted by: Fox5
Eh, maybe gravity holds the atom together, and when there's more mass there's a strongest effect on the electrons! Pseudo-science rawks.

Actually it is the electrical force caused by the attraction of electrons and protons that holds the electrons to the atom.

Yes, but there's a much weaker gravitional force involved as well, which may or may not have an effect. Though like I said, I just made that up. Thankfully, there are other people here who seem to know what they're talking about.

 

[Intelman07]

Perhaps someone can shed light on quantum mechanics, and how to grasp the concept of electrons 'disappearing' from one energy level to 'appear' on another. Where is it inbetween? Does it transport or like how can something just disappear, and reappear?

 

[Fox5]

Maybe the charge just travels through the matter in between until it reaches where it wants to be?

 

[JonB]

How does adding 3 neutrons to U 235 to make U 238, make it more stable and less useful for making a bomb? Also, does this theory explain why a certain isotope of an element follows a specific radioactive decay path and can we use it to predict other radiodecay paths?

Back to the first statement - U238 doesn't exist because of the addition of three neutrons to U235. Mathematically, that works, but in the real world, the first neutron addition will almost always result in a fission of the short lived U236. Naturally occurring deposits of Uranium have a much, much higher ratio (about 99 to 1) of U238 to U235 (the only naturally occurring isotopes worth worrying about) because U235 has a shorter half-life and has decayed or fissioned down to lighter elements like Lead. Mined Uranium must be processed with various isotope concentration methods to get the U235 percentage up to 4 or 5% before it is usable as nuclear fuel in a commercial plant. If this was an easy process, everyone would do it. Since the percentage of U235 must be orders of magnitude higher to make a fission bomb, that is much harder still.

As far as fission goes, U235 only likes to absorb neutrons that are near the same thermal energy. That is actually pretty hard to do, since free neutrons tend to have very high thermal energy. Nuclear reactors do this by using lots and lots of water to slow the neutrons. U238 likes faster, high energy neutrons, but is more likely to just absorb it and then not fission. Sometime later, the U239 will decay and give you a more useful P239 (Plutonium). P239 is very fissionable and therefore adds to the power a commercial nuclear plant produces from its fuel.

 

[DrPizza]

Originally posted by: Fox5

Originally posted by: KingofCamelot

Originally posted by: Fox5
Eh, maybe gravity holds the atom together, and when there's more mass there's a strongest effect on the electrons! Pseudo-science rawks.

Actually it is the electrical force caused by the attraction of electrons and protons that holds the electrons to the atom.

Yes, but there's a much weaker gravitional force involved as well, which may or may not have an effect. Though like I said, I just made that up. Thankfully, there are other people here who seem to know what they're talking about.

given the relative strengths of the forces, the gravitational force is pretty negligible.
Just a rough comparison of forces (just grabbed one from a quick google search)
if the strength of the strong force is 10,
then the strength of the electromagnetic is 10^-2,
weak nuclear 10^-13
gravitational 10^-42

it's like comparing a grain of sand (roughly 1x10-6 kg)
to the mass of the Earth. (roughly 6x10^24 kg)
Or, rather, the mass of a grain of sand to the mass of a few billion earths.
quite insignificant, huh?

 

[sao123]

Back to the first statement - U238 doesn't exist because of the addition of three neutrons to U235. Mathematically, that works, but in the real world, the first neutron addition will almost always result in a fission of the short lived U236. Naturally occurring deposits of Uranium have a much, much higher ratio (about 99 to 1) of U238 to U235 (the only naturally occurring isotopes worth worrying about) because U235 has a shorter half-life and has decayed or fissioned down to lighter elements like Lead. Mined Uranium must be processed with various isotope concentration methods to get the U235 percentage up to 4 or 5% before it is usable as nuclear fuel in a commercial plant. If this was an easy process, everyone would do it. Since the percentage of U235 must be orders of magnitude higher to make a fission bomb, that is much harder still.

As far as fission goes, U235 only likes to absorb neutrons that are near the same thermal energy. That is actually pretty hard to do, since free neutrons tend to have very high thermal energy. Nuclear reactors do this by using lots and lots of water to slow the neutrons. U238 likes faster, high energy neutrons, but is more likely to just absorb it and then not fission. Sometime later, the U239 will decay and give you a more useful P239 (Plutonium). P239 is very fissionable and therefore adds to the power a commercial nuclear plant produces from its fuel.

I didnt mean to imply that you would take U235 and bombard it with neutrons till it captured 3 to become U238 literally... I was asking based on the number of nuclear particles, the shape and bonding energies must have some sort of pattern with some configurations more stable than others. In other words... the position of the 3 neutrons that U238 has that U235 doesnt, must causes the shape of the nucleas to change and that would account for relieving some hidden nuclear strain which makes it a more stable nuclei.