who known a sturcture of nuke clear bomb?  

Take two lumps of enriched plutonium, which together have a critical mass. (Please keep these apart at this stage)

Next take a big hammer and give this to your GF

Now paint a very nice picture of your face on one lump of plutonium and place it on top of the other block in a room with your GF.

Call your GF all sorts of hideous insults and quickly leave the room and lock the door, enter you lead-lined bunker and remain there for 9,999,999 years.

Your GF in a fit of peak will undoubtedly hit your likeness painted on the uppermost block of Plutonium with the hammer forcing it into intimate contact with the other block, thus achieving critical mass. This will initiate an uncontrolled nuclear reaction and the subsequent extinguishing of all life for a considerable radius, eyeballs melting etc.

Don't worry you will be perfectly safe in your bunker, you did remember to install a recalculating air system and stock up on food and water didn't you?

all the best and good luck with the bomb urban