Verbal agreements are only as good as the paper they are written on. If your friend hasn't paid you for almost a year I wouldn't hold my breath waiting. Just be glad it only cost yo $500 to find out how good a friend they were. It could have cost you thousands of dollars.
Nuclear Materials. Nuclear materials are the key ingredients in nuclear weapons. They include fissile, fussionable and source materials. Fissile materials are those which are composed of atoms that can be split by neutrons in a self-sustaining chain-reaction to release energy, and include plutonium-239 and uranium-235.
There are two types of nuclear reaction, fusion and fission. Fusion is what the sun uses to generate energy --- the process in which light atoms combine and form heavier atoms. Fission is used in nuclear reactors and requires the atoms to be split, forming smaller atoms. There are four radioactive fuels used in nuclear reactors, although uranium is by far the most commonly used. Uranium is the most commonly used reactor fuel as it is the most common usable element. Different isotopes of uranium can be used, with uranium 235 the most widely used, although uranium 233 is also available for this task.