It is estimated that between one-half to two-thirds of the value of all U.S. currency in circulation is outside of the U.S. In 1934, the $100,000 Gold Certificate became the highest denomination ever issued. It was never intended for public use. Instead, it was meant solely for official transactions between Federal Reserve Banks.
Enriched uranium. Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight. 235U is the only nuclide existing in nature that is fissile with thermal neutrons.
This is because U 235 is  fissionable , meaning that it starts a nuclear reaction and keeps it going. Normally, the amount of the U 235 isotope is enriched from 0.7% of the uranium mass to about 5%, as illustrated in this diagram of the enrichment process.he gas centrifuge uranium enrichment process uses a large number of rotating cylinders in series and parallel formations. Centrifuge machines are interconnected to form trains and cascades. In this process, UF 6 gas is placed in a cylinder and rotated at a high speed.