<P> Metals creep, harden, and become brittle under the effect of radiation . </P> <P> Foods and medical equipment can be sterilized with radiation . </P> <Table> <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> <Tr> <Td> </Td> <Td> krad: </Td> <Td> typical radiation tolerance of ordinary microchips </Td> </Tr> <Tr> <Td> 4 to 8 </Td> <Td> krad: </Td> <Td> typical radiotherapy dose, locally applied </Td> </Tr> <Tr> <Td> 10 </Td> <Td> krad: </Td> <Td> fatal whole - body dose in 1964 Wood River Junction criticality accident </Td> </Tr> <Tr> <Td> </Td> <Td> Mrad: </Td> <Td> typical tolerance of radiation - hardened microchips </Td> </Tr> </Table> <Tr> <Td> 25 </Td> <Td> rad: </Td> <Td> lowest dose to cause clinically observable blood changes </Td> </Tr>

What is the difference between the units rem and rad