Characters are classified into categories via the RAD scale. The RAD scale is a measurement of theoretical radiation resistance, created by Dr. X. The RAD scale is performed by collecting some form of cellular sample of the person, and then introducing it to the 0.003 ms half-lifespan of Element-446, measuring how long the sample's cells survive.
Degrees apply to the half life, meaning a degree of two requires the ejected equivalent of 0.006 ms, but since the half life is this fast, the degree instead changes the amount of atoms in the radioactive element. So for example, to get the scale for 3 degrees, multiply 1 by 2 by 1.25. Equations are simplified below.
x = Level, y = cell survival time, z = degree.
A-RAD: Radioactive degree of 1. (y / z(0.003) ) A-RAD kills regular people and superhumans
B-RAD: Radioactive degree of 2. (y / z(0.003) ) B-RAD kills people who are between superhuman and Godlike
G-RAD: Radioactive degree of 1.25. (y / z(0.006) ) G-RAD kills Godlike entities
D-RAD: Radioactive degree of 2.5. (y / z(0.075) ) D-RAD kills anything above G-RAD and below E-RAD, since some organisms are naturally in a weird place between cellular resistance and weakness, via the same system in energy that creates the measure of RAD, so the system has a weird middle zone where this level exists.
E-RAD: Radioactive degree of 5. (y / z(0.01875) ) E-RAD kills anything beyond God level, or anything capable of instant cell regeneration.
OM-RAD: Radioactive degree of 10. (y / z(0.09375) ) OM-RAD kills anything, and is the final peak of radiation.
VOID: Void literally just means that this organism is capable of surviving in a completely empty environment, or vacuum. This is not a degree of RAD technically, but it does mean that this organism is not affected by RAD via some form of resistance.
The RAD test works upwards, testing for X via Y as it relates to Z, and if the level is greater than or equal to 1, the cells pass onto the next level. A new sample is obviously required per test, and if the cells generate X<1, the character immediately sits there, regardless of it's results in higher categories, and regardless of thread potential. This tests specifically for the initial cell death.