memorandum, written in England by Otto Frisch and Rudolf Peierls, contains all the fundamental elements of nuclear warfare technology: it speaks of a super-bomb that would use the energy of the atomic nucleus, producing an explosion of 1,000 tons of dynamite, with temperatures comparable to those reached in the interior of the Sun, capable of destroying the center of a large city. This would cause the dispersion of radioactive substances, which would decay only gradually over several days, capable of killing anyone who came near even after the explosion. These substances could also be carried by winds for miles. To make this, the memorandum states, the light isotope U235 from Uranium 238 would be needed: a difficult task, but, it concludes, not insurmountable. The critical mass is calculated at about one pound, and a mechanism is envisioned that combines two subcritical masses.
