Love the detail. Interestingly, Cockroaches aren't even among the top contenders to best survive a nuclear holocaust.

So, humans will die off at about 4-10 radiation units (GY).
Cockroaches? between 100-9,000!!
Tardigrade (water bear)? - 5,000
Some bacteria? 15,000
Archaea? 30,000

There's something to be said for the little guys...