Thanks for the input!
I really can’t wait for 2.5! I’m going to remake this whole animation once I have it!
And yes, I had to use billboards, it was the only way I could get shading and shadows to work correctly…it was extremely frustrating. I settled on a darker cloud after the fireball fades because if I lit the “smoke” any more, it wound up looking like “little spheres” and looked dumb.
There’s a material IPO lighting the color of the smoke over time, but I cut off the animation before it fades to a grayish color because, again, it looked a little goofy.
@ROUBAL: Thanks for the comments! I’m not pretending to be a professional on the subject, as I’ve never had any professional training in dealing with nuclear weapons.
I gathered my data from a few interesting web resources: If you’re interested in some technical reading, here’s a quick overview here. If you REALLY want to learn about nuclear fission weapons in great detail look here.
The 2nd link is a book. This book, completely published in pdf, is where I got the equations to make my simulator. It provides the equations that, given a “yield” or size of weapon, you can calculate initial prompt ionizing radiation, conversion to isothermic radiation, size and rise rate of the cloud over time, and the shock wave speed. It even provides a method for calculating mach effect—where the shockwave from the bomb meets the reflection shockwave from the ground, amplifying the initial shockwave and making it twice as deadly for twice the range. My simulator based on this, allows you to experiment with yields at different detonation heights to optimize “kill” distance. Yep, it’s a sick science!
According to this book, prompt ionizing radiation–gamma rays and soft x-rays, only last about 100th of a second for a 10 kiloton yield. Since our atmosphere is essentially opaque to this type of radiation, it undergoes a series of absorbing, and re-radiating only tens of meters around the bomb. This is where the secondary pulse you were explaining comes from. This secondary pulse is emitted from the explosion only after two things must occur. The shockwave compresses the air into a plasma at the onset of the explosion, making the shockwave incandescent, and yet considerably dimmer than the initial pulse. The air around the shockwave must become transparent again so it can no longer act as a “shutter”, and the ionizing radiation must be absorbed and re-radiated long enough to be emitted in visible wavelengths (light and heat) hence, the isothermic pulse. For 10 kt yield, this second, thermal pulse lasts about 0.6 seconds after the blast. Up to 1 second for a 1 megaton yield.
They say that while witnessing a real weapon detonation, you see an initial violet colored flash before the shockwave masks the core of the explosion. I even put this in my animation, however, you can’t see it because it was too quick to show up at 25 frames a second! Oh well.
