Re the "Gamma Bomb"
That would be a regular Nuclear Weapon.
(Gamma Rays, X-Rays, Alpha & Beta Particles, etc..)
They changed the origin in the other Hulk movie because in this day & age everyone
should know what Gamma radiation really does.
The Audience's perception of "Realistic" Science in Science Fiction progresses through the years.
Back in the sixties, people really believed that dropping an atom bomb on an Ant, or a Spider or a Dachshund would make it grow gigantic or give a Human phenomenal abilities..
Film makers today have a difficult job in this, nowadays.. coming up with explanations why there's a Giant Firebreathing Dinosauroid stomping on Downtown Osaka or explaining how an ordinary Human can turn green and grow from 5'10" & 190 pounds to 12"6' & 2500 pounds.
I'm glad I ain't got that job.
"Names in the new order were Totem signs, no longer mere markers for a face.
Markers were for tombstones."