The Prismatic Hammer can be found on the Groundbreaker. Enter the bunk room to the left of the Promenade entrance and climb onto the beds. Sneak into the hidden room through the vent, and kill the guards to collect a key to the locked door —- the Prismatic Hammer is inside.
The Prismatic Hammer has a strong Power Attack, and deals all elemental damage types at the same time. Bring characters with perks that increase Science Weapon Damage, and select perks of your own that increase it further. You can boost Science Weapon Damage by +120% with Vicar Max and your character perks.