Thanks, that’s more in line with what I remembered.
What is the appropriate term if decay isn’t it? Just split?
As in “in an atom bomb Uranium x into this and that”
Fissions.
Well I used to be a physicist, but a terribly bad one, so don’t trust me too much, but decay is generally accepted to be a small change in atomic mass through one of the common forms of decay (alpha, beta (in all its forms) and gamma)
When it is undergoing fission , which is to say splitting into two substantial parts that are not covered by the above decay mechanisms, I beleive it would be correct, if a little clumsy,to say the uranium atom fissioned into x and y, but most of the time people go with ‘split’.
Addendum: There are at least two known processes which can convert matter to energy with 100% efficiency, and one more which can achieve 50% efficiency. All three of them, of course, are far beyond our level of technology, and only the third one has ever been observed in nature.
Well, my apologies for spreading mis-info with post #14. 
For some reason, I failed to consider that the article(s) was discussing natural decay vice chain reaction fission.
Isn’t there a rule against teasing? Tell us what they are.
I also would like to know what the other way of converting 100% to energy is. One of them is fairly obvious.
As to the 50% one, I’m guessing it’s either gravity waves of black holes encircling each other or fusion/x-rays from matter falling into a black hole.
Sorry, I guess I should follow up on that. The first way is to feed the matter into a black hole, and wait for it to come back out as Hawking radiation. Hawking radiation is mostly massless particles (what most folks would consider “energy”), and has no preference for matter vs. antimatter (no matter what was fed in), so anything that wasn’t already massless, you could annihilate to produce energy. Unfortunately, Hawking radiation depends on the size of the black hole, and for any black hole known to exist in the Universe, it’s pathetically weak. You’d need a very small hole to make this practical.
The second method is proton decay: Most current theories predict that the proton will eventually, after a very long time, decay, producing a positron and a bunch of other stuff. Again, anything that isn’t already massless could be annihilated with other reaction products to produce stuff that is. The problem here is that proton decay is phenomenally slow, and would ordinarily take many times the lifespan of the Universe. On the other hand, the same theories which predict it also predict that it should occur much, much faster (fast enough to be practical) in the presence of a magnetic monopole. So the problem is just one of finding or making a monopole.
The third process is to drop things into a black hole, and extract the gravitational potential energy as you do so. Some inevitably gets into the black hole, but you can in principle get an output of up to half of the mass you started dropping in. You can use any size black hole whatsoever for this one. This is basically the process which powers quasars, though there it’s uncontrolled and a lot less efficient.
What about antimatter ? That’s a 100% conversion process, and it’s one we can perform even with our technology on a tiny scale.