You are a walking nuclear reactor, or a reasonable facsimile thereof. The seething energies inside you are toxic to most lifeforms. For you, it's food. Fuel. Power to fight with. With your radiation, you can damage foes' bodies, making them queasy and sometimes unable to fight back.
Some Radiation Blast features require an attack roll. In all such cases, you are making a ranged attack that you are proficient with, and you add your Dexterity Modifier to the roll. You also add your Dexterity Modifier to the damage.
At 1st level, you can use your Action to shoot a blast of pure radiation at a target that you can see within 80 feet. Make a ranged attack roll. If successful, the target suffers radiant damage equal to 2d8 plus your Dexterity Modifier. If your attack roll is a critical hit, your target is vulnerable to radiant damage until the end of its next turn.
You can use X-Ray Beam at 1st level, Proton Volley at 3rd level if you are a Corruptor, or at 4th level if Radiation Blast is your Primary Power Set and at 6th level if it is your Secondary Power Set, and Cosmic Burst at 7th level if Radiation Blast is your Primary Power Set and at 11th level if it is your Secondary Power Set.
At 1st level, you can use your Action to send a pulse of intense radiation outward from your body. Each creature within 20 feet of you must make a Constitution Saving Throw or take 2d8 radiant damage and become vulnerable fire, force, and radiant damage until the end of its next turn. If the creature's Saving Throw succeeds, it takes half damage and only becomes vulnerable to radiant damage.
You can use Neutron Bomb at 10th level if Radiation Blast is your Primary Power Set and at 14th level if it is your Secondary Power Set and Atomic Blast at 12th level if Radiation Blast is your Primary Power Set and at 15th level if it is your Secondary Power Set.
At 2nd level if Radiation Blast is your Primary Power Set or at 4th level if it is your Secondary Power Set, you can use your Action to release a blast of free electrons in a cone 40 feet long and 20 feet wide. Each creature in that area must make a Constitution Saving Throw. If the roll fails, all attack rolls against the creature have advantage and all Dexterity Saving throws may by the creature have disadvantage until the end of its next turn. If you add at least one Endurance Die to the DC for this feature and the target fails its roll, it is knocked prone.
At 3rd level if you are a Blaster, or at 4th level if Radiation Blast is your Primary Power Set or at 8th level if it is your Secondary Power Set, you can take a moment to focus your senses. Roll at least one Endurance Die. You can add the result to every Radiation Blast attack and damage roll you make until the end of your next turn. Using this feature does not cost an Action but you can only do it on your turn.