Radiation Units

Physical Quantity

Modern Unit
(SI Unit)
Old Unit 
(quasi-cgs unit)
Radiation Dose
Concept: Energy per unit mass

1 Gy = 1 joule/kg


1 rad = 1 erg/gram

Radiation Dose Equivalent
Concept: the dose that is equivalent (in terms of effect on cells) to a dose of 100-keV x-rays

Since (for example) neutrons have about 20 times as much effect on cells as x-rays (for the same dose),
1 milligray of neutrons amounts to 20 millisieverts.

1 rad = 0.01 Gy
1 rem = 0.01 Sv
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