[LeeE]

Umm... that should be U-238 Joe, not 258, and only a very small percentage of the mass in a simple fission bomb (which actually needs U-235 or Pu-239) is actually converted into energy.  It still amounts to a very large amount of bang for a very small amount of matter through.

In fact, U-238 can only be used as fuel in a fission-fusion-fission type bomb, where the U-238 is fissioned by the high-speed neutrons produced by the secondary fusion stage.  The secondary fusion stage needs to be ignited by a fission primary though, and as mentioned, this must be either U-235 or more commonly Pu-239 (which can be produced from the more common U-238).

[Joe L. Ogan (OP)]

OK, Thanks for the information.  My memory may be a little off on the actual number.  Thanks for comments.  Joe L. Ogan

[Farsight]

You say that energy consists of both energy ("hot body") and mass ("weighs more"), and that relativity never seems to be explained properly.  I know E = mc² regarding the creation/annihilation/conversion of mass and energy.  So you seem to be saying that the real input/increase of energy into a hot(ter) body is:

ΔEnergy = ΔEnergy_heat + Δm_ΔEnergyheatc²

Sorry Dave, I've been tied up. No, I didn't mean the above. The delta energy is due to the heat alone. If you look closely at say a container of gas, when you heat it the individual molecules move faster, temperature being a measure if their average motion. Whilst no one molecule has a greater mass, the overall mass of the container of gas is increased.   

[lightarrow]

It is incorrect to say that:

A system's mass is nothing else that the energy contained inside that system (divided by the constant c2)

for they are clearly different; if they were not, we would all be living in radiation and not matter.  However, matter and energy may be inter-converted and so may be considered equivalent in the same sense that a tank full of heating oil is equivalent to a warm home in winter.  You only need to try living in a tank full of heating oil to spot the difference between them though.

1. "Matter" is not "mass". The first means "particles with non zero rest mass", the second means E/c².
2. As I explained a lot of times, the system have to be still, or you cannot use E = mc². A photon cannot be still, so you can never use E = mc² so you cannot say that for a photon the mass is E/c². Infact it's massless...
3. Suppose you havea box with two holes and a laser light pulse enter one hole and exit the other. During the little interval of time in which the light pulse can be localized (or part of it) inside the box, the box acquires a mass m = E/c² if E is the light pulse's energy.

Sigh...  more nonsense.

The reason that E=mc² cannot be applied to photons is because [the photon], as you eventually point out...

Infact it's massless...

...so of course if you tried to apply E=mc² to a photon you'd end up with a big fat 0.  It's got nothing to do with whether the photon is 'still' or not.

So, all of my explanations and you still haven't understood... []
Please, read again what E = mc² really means (I've explained clearly).

I'll also just remind you that there is no absolute frame of reference, so the notion that anything is 'still' is purely relative.

Another meaningless phrase...
For you, a bullet which is still in your frame of reference or that is moving towards you at 900 m/s is the same thing?  []
In the first case you write E = mc², in the second you have to write E² = (mc²)² + (cp)². Is it so difficult?

About photons: if one day we'll be able to find an extremely little but non zero mass of the photon, then, authomatically, we'll have discovered the existence of a frame of reference where they are not moving. Think about neutrinos, they were believed to be with zero mass for decades and now recent, very sensitive measures seems to indicate they have a non zero mass (= you can stop them).

[Farsight]

Do you honestly really think that an electron is just a photon that's orbiting an atomic nucleus?

Not at all. I think you've misread something there. A photon "going round and round" is an electron or a positron depending on the chirality. Do read http://arxiv.org/abs/physics/0512265. It might be unfamiliar to you, but it's a bona-fide peer-reviewed paper.  

Electrons are not only made as a consequence of combining two photons but also as a result of free neutron decay.

Yes, Beta-minus decay. It's very informative.

Also, you can't employ pair production to 'split' a photon; that's rather like putting the cart before the horse. What happens is that a high-energy photon interacts with other matter (usually an atomic nucleus) and the electron-positron pair are produced as a result.

And if there's not enough energy they annihilate, and the result is (usually) two 511keV photons. The original photon is definitely split.

The electron in the pair is very unlikely to end up being 'adopted' by the atom that produced it, and end up going round and round instead of laterally.

As above. The photon going round and round is the electron. Another paper offering what is essentially the same model is "Is the electron a photon with a toroidal topology?" Williamson and van der Mark, Annales de la Fondation Louis de Broglie, Volume 22, no.2, 133 (1997). You can access it and a draft new paper at http://www.cybsoc.org/cybcon2008prog.htm#jw.
  

Incidentally, what do you think happens to the positron that's also produced? You fail to mention its fate.

Typically the electron and the positron fly off with some considerable velocity. The positron is likely to meet an electron and annihilate.  

[Farsight]

Sigh...  more nonsense. The reason that E=mc² cannot be applied to photons is because [the photon], as you eventually point out, [is massless], so of course if you tried to apply E=mc² to a photon you'd end up with a big fat 0.  It's got nothing to do with whether the photon is 'still' or not.

I'm afraid this really is how it works Lee. It lies at the heart of relativity, is the very basis of E=mc², and dates back to 1905. It certainly isn't nonsense. If a body emits radiation, it loses mass. That body can be a mirrored box containing photons.

Run the scenario in reverse and trap a photon in a mirrored box, and the mass of the system is increased. Think about the expression E² = (mc²)² + (cp)², and consider the initial photon in pair production. It has no mass, so E² = (cp)². After pair production, examine the electron, considering it to have zero velocity with respect to you. Then E² = (mc²)². Annihilate the electron and you've flip-flopped back to E² = (cp)². Pair production and annihilation demonstrate the symmetry between momentum and inertia by creating and destroying a system called an electron, along with another system called a positron. In such a system, the photon is still moving at c, but it is no longer moving in aggregate with respect to you. Hence its energy/momentum is exhibited as inertia. Mass.         

[LeeE]

Sigh...   a little knowledge...

[Farsight]

It really is like this Lee. Please refer to a trusted expert on relativity, who will confirm that the mass of a system is a measure of energy content, and a trapped photon increases the mass of the system that traps it.

[Joe L. Ogan (OP)]

I ain't gonna argue with either one of you guys, you are too damn smart for me.  Regards, Joe L. Ogan