Nuclear Physics - Where elements come from and go to

[Yora]

I love physics, but never really got into it because I suck at math and can't calculate anything. But all the models of how stuff works and interacts are often not that difficult to understand, even if you're unable to calculate how much, how fast, how long, or how far of something you'd get in practice.

Currently I am quite interested in Uranium and Plutonium. And I came on this curious paragraph at wikipedia: "Plutonium-238 was the first isotope2 of plutonium to be discovered. It was synthesized by Glenn Seaborg and associates in 1941 by bombarding uranium-238 with deuterons [hydrogen-2], creating neptunium-238, which then decays3 to form plutonium-238. Plutonium-238 decays to uranium-234 and then further along the radium series to lead-206."

Is that correct? Shouldn't uranium-238 plus hydrogen-2 lead to neptunium-240?

Every element is defined by its number of protons. 1 proton is hydrogen, 2 protons is helium, 3 protons is lithium, and so on. The number of protons is the atomic number.
All elements (except hydrogen) always also have a number of neutrons in adition to the protons. The number of neutrons can be different or changed, but as long as the number of protons are the same, it's always the same element. The combined number of all protons and neutrons is the mass number. Two atoms of the same element (same number of protons) but a different number of neutrons are called different isotopes of that element. Uranium-236 is an isotope of 236 particles (92 protons + 124 neutrons) and uranium-238 an isotope of 238 particles (92 protons + 126 neutrons).
A neutron can be thought of as a proton that is fused together with an electron. Since the electron has almost no mass, the mass of a proton and a neutron is still almost the same. A neutron can also fall apart again and turns into a proton again, shoting the electron away. Since electrons radiated from an atomic core are called beta radiation, the process of a neutron turning into a proton is called beta decay.

[IthilanorStPete]

I love physics, but never really got into it because I suck at math and can't calculate anything. But all the models of how stuff works and interacts are often not that difficult to understand, even if you're unable to calculate how much, how fast, how long, or how far of something you'd get in practice.

Currently I am quite interested in Uranium and Plutonium. And I came on this curious paragraph at wikipedia: "Plutonium-238 was the first isotope2 of plutonium to be discovered. It was synthesized by Glenn Seaborg and associates in 1941 by bombarding uranium-238 with deuterons [hydrogen-2], creating neptunium-238, which then decays3 to form plutonium-238. Plutonium-238 decays to uranium-234 and then further along the radium series to lead-206."

Is that correct? Shouldn't uranium-238 plus hydrogen-2 lead to neptunium-240?

Every element is defined by its number of protons. 1 proton is hydrogen, 2 protons is helium, 3 protons is lithium, and so on. The number of protons is the atomic number.
All elements (except hydrogen) always also have a number of neutrons in adition to the protons. The number of neutrons can be different or changed, but as long as the number of protons are the same, it's always the same element. The combined number of all protons and neutrons is the mass number. Two atoms of the same element (same number of protons) but a different number of neutrons are called different isotopes of that element. Uranium-236 is an isotope of 236 particles (92 protons + 124 neutrons) and uranium-238 an isotope of 238 particles (92 protons + 126 neutrons).
A neutron can be thought of as a proton that is fused together with an electron. Since the electron has almost no mass, the mass of a proton and a neutron is still almost the same. A neutron can also fall apart again and turns into a proton again, shoting the electron away. Since electrons radiated from an atomic core are called beta radiation, the process of a neutron turning into a proton is called beta decay.

Seaborg's summary of the work (http://www.osti.gov/scitech/servlets/purl/5808140) mentions that the bombardment of U-238 with deuterium also produced two neutrons in addition to Np-238. The neptunium then decayed to Pu-238 by beta decay.

Incidentally, characterizing neutrons as "a proton fused with an electron" is incorrect; beta decay occurs due to a down quark within the neutron changing to an up quark, releasing a W- boson, which then decays to an electron and electron antineutrino.

[Yora]

Okay, that adds up.

But that makes me wonder: Do all elements beta decay all the tame? Why don't all elements change everyday?

[BannedInSchool]

But that makes me wonder: Do all elements beta decay all the tame? Why don't all elements change everyday?
From Wikipedia on beta decay (http://en.wikipedia.org/wiki/Beta_decay):

Most naturally occurring isotopes on Earth are beta stable. Those that are not have half-lives ranging from under a second to periods of time significantly greater than the age of the universe.

[Yora]

But why?

Do the neutrons "know" in any way that they "have" to decay to reach some optimal state in the nucleus?

[Spiryt]

But why?

Do the neutrons "know" in any way that they "have" to decay to reach some optimal state in the nucleus?

http://en.wikipedia.org/wiki/Neutron–proton_ratio


I think that this would anwer it?

[Sith_Happens]

Seaborg's summary of the work (http://www.osti.gov/scitech/servlets/purl/5808140) mentions that the bombardment of U-238 with deuterium also produced two neutrons in addition to Np-238. The neptunium then decayed to Pu-238 by beta decay.

Yeah, letting off neutrons when it gets hit by stuff is kind of uranium's defining feature.

[BannedInSchool]

But why?

Do the neutrons "know" in any way that they "have" to decay to reach some optimal state in the nucleus?

Uh, is saying that the stable isotopes are the lower energy states, radioactive decay is a nucleus spontaneous falling from higher to lower energy, similar to the way atoms emit photons or dominos on a narrow edge fall over, and that nuclei with a stable ratio of protons to neutrons isn't going to spontaneous fall further and release more energy enough of a "why"? Or do you need why too many protons or too many neutrons is higher energy than the stable number?

[Yora]

Just looking at the single neutron (if that makes sense, quantum physics can be weird), is it affected by the protons and other neutrons around it?
If I understand it correctly, a single neutron does not spontaneously beta-decay, only when it's in a nucleus with other neutrons and protons. So, I would guess, the presence of the other particles must have some effect on the neutron. Is that the Weak Force? I never understood what that one does.

[BannedInSchool]

Just looking at the single neutron (if that makes sense, quantum physics can be weird), is it affected by the protons and other neutrons around it?
If I understand it correctly, a single neutron does not spontaneously beta-decay, only when it's in a nucleus with other neutrons and protons. So, I would guess, the presence of the other particles must have some effect on the neutron. Is that the Weak Force? I never understood what that one does.
Until someone who knows what they're talking about answers :smallsmile: it's the strong force holding protons and neutrons together and in a way they're all quarks interacting quarkily with each other. However, it's the weak force/interaction that's responsible for neutrons decaying and they'll do it as free neutrons too. Friend Wikipedia (http://en.wikipedia.org/wiki/Neutron) says on average in 15 minutes, and that page has a lot of stuff that's basically this thread, heh.

[Max™]

Basically what was said about the energy states is really the easiest way to look at these processes.

If it takes more energy to liberate a particle than it does to sit in a given state then it will remain in that state for a period of time related to the likelihood of random fluctuations bumping it into a high enough state to decay.

Certain configurations of particles fall into those stable states readily, certain configurations can be encouraged to move towards a given state or another by following a path which they wouldn't normally, and certain configurations have multiple routes which they can follow to a lower energy state.

The domino metaphor isn't bad, but it's more 2-D, while decays occur through a phase space with, lets just say "many" degrees of freedom.

So a big multi-dimensional arrangement of dominos, there are lots of ways to set them up that won't last long, there are a few ways which can last a short period, and there are even fewer ways which have arbitrarily long periods of stability. More dominos have more ways to fall over quickly than stable ones so heavier and heavier elements decay ever more rapidly.

[Sith_Happens]

Basically what was said about the energy states is really the easiest way to look at these processes.

If you remember the concept of atomic orbitals, the nucleus can also be modeled as a set of orbitals, the math is just orders of magnitude more complicated because the particles are interacting to a significant degree (in three different ways, no less).


If it takes more energy to liberate a particle than it does to sit in a given state then it will remain in that state for a period of time related to the likelihood of random fluctuations bumping it into a high enough state to decay.

Mostly correct. Radioactive decay is usually due to tunneling rather than excitation.

...Or are the "fluctuations" here just a different way of saying that?