<Tr> <Td> 25 </Td> <Td> rad: </Td> <Td> lowest dose to cause clinically observable blood changes </Td> </Tr> <Tr> <Td> 200 </Td> <Td> rad: </Td> <Td> local dose for onset of erythema in humans </Td> </Tr> <Tr> <Td> 400 </Td> <Td> rad: </Td> <Td> whole body LD for acute radiation syndrome in humans </Td> </Tr> <Tr> <Td> </Td> <Td> krad: </Td> <Td> whole body LD for acute radiation syndrome in humans </Td> </Tr>

The measurement of radiation energy (x-ray or gamma radiation) in air per unit of time is the