1. Roentgen
A unit used to express radiation exposure is the Roentgen.
More information:
Roentgen (R) or röntgen is an measurement unit for measuring radiation exposure.
It was defined as the x-rays amount that produced 2.580 × 10-4 coulombs of charge collected per unit of weight (kilograms) of air at normal temperature and pressure (STP): 1 R = 0.000258 Ckg-1 in the air.
Basic SI units: 2.58 × 10−4 A⋅s/kg