Subject: U236 and long half life

when u235 is hit by a neutron, it becomes u236 and breaks up immediately, like
in the atom bomb. I'm confused at this point - when this was explained to me, i
understood that u236 was extremely unstable, and i thought the rapid decay was
due to its half life being short, and instead of normal radiation, fission
occurs. I looked up the half life of U236 and found it to be in millions of
years, and am in a bit of a puzzle. 

Re: U236 and long half life