DonFerro and Enzo,
Here is another recipe for you guys to try:
Industrial fly-ash - 40%
Enriched radio-active uranium - 40%
Coolant Liquid - 8%
Sulphuric-acid - 8%
Methane - 1%
Naphta+Asphalt - 2%
Bacteria Culture - 1%

Note: You can substitute Fly-ash with 99% pure cement+asbestos mixture