Let's just say that basic nuclear physics is above your pay grade.
An exploding nuclear weapon instantly vaporizes itself. What was cold, solid material microseconds earlier becomes a gas hotter than the Sun’s 15-million-degree core.
This hot gas radiates its energy in the form of X-rays, which heat the surrounding air. A
fireball of superheated air forms and grows rapidly; 10 seconds after a 1-megaton explosion, the fireball is a mile in diameter. The fireball glows visibly from its own heat — so visibly that the early stages of a 1-megaton fireball are many times brighter than the Sun even at a distance of 50 miles. Besides light, the glowing fireball radiates heat.
This
thermal flash lasts many seconds and accounts for more than one-third of the weapon’s explosive energy. The intense heat can ignite fires and cause severe burns on exposed flesh as far as 20 miles from a large thermonuclear explosion. Two-thirds of injured Hiroshima survivors showed evidence of such flash burns. You can think of the incendiary effect of thermal flash as analogous to starting a fire using a magnifying glass to concentrate the Sun’s rays. The difference is that rays from a nuclear explosion are so intense that they don’t need concentration to ignite flammable materials.
