Nuclear Bomb - The Explosion
The distinctive double flash of a nuclear detonation.
take a moment to talk about what happens during the first few milliseconds when
a nuclear explosion happens. When the explosion begins, the device itself
quickly goes to a temperature of about ten million kelvins. The X-rays and
ultraviolet waves emitted heat the air within a few meters of the device to a
temperature of about one million kelvins, which makes it extremely incandescent
and causes an incredibly bright flash. Meanwhile, inside that cloud of bright
gas, a shockwave expands, pushed by the explosion itself. Inside that shockwave,
everything is a plasma, where the atomic particles are actually dissociated.
Plasmas are opaque, because they absorb electromagnetic radiation at all
frequencies. As that shockwave expands, it overtakes those first few meters of
incandescent air, and once it does, its opacity actually shades it like a
curtain. From there, the shockwave expands outward spherically; and as the
plasma thins and diminishes it becomes increasingly transparent, allowing the
expanding fireball to shine forth with its full brilliance. Thus, when a nuclear
explosion happens, we actually get a double flash. The larger the yield, the
longer the space between the flashes; ranging from 30 milliseconds for the
smallest devices to half a second for larger ones.