>Carbon-14 and carbon-12 are different isotopes of carbon ... right?

Yes.

Yes, that's right.

They're often used interchangeably, but that's not technically correct.

A nuclide is a collection of nucleons defined by its number of protons (Z) and number of neutrons (N).

Isotopes are nuclides that have the same Z. So they are the same element, but they can have different numbers of neutrons.

The single photon is emitted in a superposition of all directions, with the angular distribution defined by the angular momentum it carries. However when you detect the photon, you entangle the state of your detector with the state of the photon such that the state of the photon decoheres to a single direction. So it looks like the photon traveled in a single, random direction, as opposed to a superposition of all directions.

If the atom is not initially polarized before it emits the photon, then the angular distribution of the emitted photon is isotropic in space.

If the atom is initially polarized, then there will be some non-uniform angular distribution based on the angular momentum change of the transition.

>A single photon strikes an atom, raising its energy level. How many photons are then re-emitted, isotropically?

There's not enough information to determine that; it depends on the level scheme of the atom. If the atom is excited to its first excited state, there can only be one photon emitted. But if it's in a higher excited state, it's possible that multiple photons will be emitted in a cascade.

>To me, wave energy propagation in all directions would no longer have a discrete direction, so how can I conceptualize the "number" of photons re-emitted?

I'm not sure what you mean here, or why you're relating the angular distribution of emitted radiation to the number of photons.

Tunneling is when the wavefunction of a quantum system is nonzero in a region of space that would be classically forbidden.

In other words, it's when there's a possibility to find a particle in a region of space that would be impossible in classical mechanics.

Free neutrons decay with a half-life of about 15 minutes. But that doesn't apply to neutrons bound inside of nuclei.

Yes.

It can, yes.

It depends on the nuclide, and the energy regime. Here are some examples.

Yes.

When uranium-235 interacts with a neutron, sometimes you get fission, and sometimes you get other processes, like radiative capture. When uranium-235 captures the neutron and de-excites via gamma emission, what's left over is uranium-236.

Time is not discrete, as far as we know.

I don't know what you think those statements have to do with my comment. The question was whether the tritium-breeding reactions can cause a chain reaction, and the answer to that is no.

RBMK fission reactors are completely different things than what we're talking about here. There's plenty of information available on what caused the Chernobyl accident, none of which is relevant to this conversation.

There will be activation of reactor components, of course. But that will not result in nearly the amount of radioactivity per unit mass as the fission products in spent fission fuel.

If you can breed fuel for a reactor, you can inherently breed fuel for a weapon too. Any spent fission fuel can in theory be reprocessed, and have material diverted for weapons purposes.

But that's why organizations like the IAEA closely monitor fuel cycles for proliferation concerns.

No, these are not like the fission chain reactions used in fission reactors. There's no way for that kind of thing to happen in this situation.

They're not all endothermic, for example ^(6)Li + n -> a + t has a positive Q-value.

The buoyancy of an object in a fluid depends on the average density of the object and the density of the fluid.

In the situations you're describing, the mass is constant and the volume is changing. So the average density is decreasing as the volume increases, and indeed, if the average density falls below the density of the surrounding fluid, the object will become buoyant.

The speed of sound is when shock waves start to form, so that's when sonic booms start.

>How much lower is this temperature?

Here is the reactivity as a function of temperature for a few candidate reactions.

>Is the main motivation of using Tritium the lower temperature or actually the breeding reaction?

The main motivation is the temperature. Obtaining fuel for DD is not an issue, because there's plentiful deuterium in nature (seawater, for example). It's a nice benefit, and quite important for tritium, which is not found naturally in large amounts. We have to produce tritium somehow, and having the reactor breed its own fuel is a nice way to do that.

>How far apart is the fusion temperature from the fusion ignition temperature and how is each one defined?

Not sure what you mean here.

The speed of sound is the speed at which infinitesimal oscillations in the density and pressure propagate through the fluid.

If an object moving through the fluid at or above the speed of sound, there's no way for any of the fluid upstream of the object to "know" that the supersonic object is coming.

And as a result, in order for conservation of mass, momentum, and energy to be upheld, you find that there must be discontinuities in the density, pressure, etc. at some point between the fluid upstream of the object and the fluid downstream of the object. These discontinuities are called shocks, and they first start to form specifically as the object reaches the local speed of sound.

Yes. Degeneracy pressure is common to all fermions.