Hellfire Isaac Asimov 

There was a stir as of a very polite first-night audience. Only a handful of scientists were present, a sprinkling of high brass, some Congressmen, a few newsmen.
Alvin Horner of the Washington Bureau of the Continental Press found himself next to Joseph Vincenzo of Los Alarnos, and said, "N 0 W we ought to learn something."
Vincenzo stared at him through bifocals and said, "Not the important thing." Horner frowned. This was to be the first super-slow-motion films of an atomic explosion. With trick lenses changing directional polarisation in flickers, the moment of explosion would be divided into billionth-second snaps. Yesterday, an A-bomb had exploded. Today, those snaps would show the explosion in incredible detail.
Horner said, "You think this won't work?" Vincenzo looked tormented. "It will work. We've run pilot tests. But the important thing ∼"
"Which is?"
"That these bombs are man's death sentence. We don't seem to be able to learn that." Vincenzo nodded. "Look at them here. They're excited and thrilled, but not afraid."
The newsman said, "They know the danger. They're afraid, too. "
"Not enough," said the scientist. "I've seen men watch an H-bomb blow an island into a hole and then go home and sleep. That's the way men are. For thousands of years, hell-fire has been preached to them, and it's made no real impression."
"Hell-fire: Are you religions, sir?"
"What you saw yesterday, was hell-fire. An exploding atom bomb is hell-fire. Literally."
That was enough for Horner. He got up and changed his seat, but watched the audience uneasily. Were any afraid? Did any worry about hell-fire? It didn't seem to him. 
The light went out, the projector started. On the screen, the firing tower stood gaunt. The audience grew tensely quiet.
Then a dot of light appeared at the apex of the tower, a brilliant, burning point, slowly budding in a lazy, outward elbowing, this way and that, taking on uneven shapes of light and shadow, growing oval.
A man cried out chokingly, then others. A hoarse babble of noise, followed by thick silence. Horner could smell fear, taste terror in his own mouth, feel his blood freeze.
The oval fireball had sprouted projections, then paused a moment in stasis, before expanding rapidly into a bright and featureless sphere.
That moment of stasis – the fireball had shown dark spots for eyes, with dark lines for thin, flaring eyebrows, a hairline coming down v-shaped, a mouth twisted upward, laughing wildly in the hell-fire-and horns.