Fabien Weibel has made this great and detailed tutorial of how to make an atomic bomb (or any other massive) explosion. The result looks really good so don’t miss this intermediate/advanced level tutorial!
Weibel writes:
After many tests, I found that the particle system was inadequate to create an atomic bomb.
So I decided to find another way to do this. It is displacement mapping.
Go to the tutorial to read more (mirror). It’s viewable in pdf-format in both English and French.
