Gray
The SI unit of absorbed radiation dose, equal to one joule of energy deposited per kilogram of matter.
Formula / equation
1 Gy = 1 J/kg
Unit
Gy
In depth
The gray measures physical energy deposition without regard to the biological effect, so one gray of alpha radiation is far more damaging than one gray of gamma. Whole-body doses above about 5 Gy are usually fatal without intensive treatment.
Examples in the real world
Radiotherapy delivering 60 Gy to a tumour in thirty daily fractions of 2 Gy.