Page 19 of classified scientific paper by US nuclear physicists Edward Teller and Stanislaw M. Ulam March 9, 1951 "On Heterocatalytic Detonations I: Hydrodynamic Lenses and Radiation Mirrors", at US nuclear weapon design facility Los Alamos Scientific Laboratory, Los Alamos, New Mexico, which contains their historic breakthrough idea for how to build a practical thermonuclear weapon, staged implosion, generally referred to as the "secret of the hydrogen bomb". This concept, which may have been independently invented by scientists in other countries, is thought to be the design used in all modern thermonuclear weapons, which includes virtually all nuclear weapons in the stockpiles of major "nuclear" nations. This declassified version is heavily redacted; out of 20 pages only a few paragraphs are not blacked out. Only pages with text remaining have been uploaded here. These last unredacted paragraphs say in part ""the essential parts of the design do not depend sensitively on complicated shapes"".