What unit is used when a dose is greater than 10 rem?

The correct choice for a dose greater than 10 rem is the rad. The rem (roentgen equivalent man) is a unit of equivalent dose, while the rad is a unit of absorbed dose. When discussing doses in the rem range, it's common to refer to the rad for higher doses because it provides a more straightforward representation of the energy deposited by radiation in a material or tissue.

For doses over 10 rem, using the rad is typically more relevant in radiological contexts where the focus is on the absorption of radiation by the body.

It's also important to note that the other units mentioned serve different purposes. The millirem (mrem) is a subunit of the rem and is used for smaller doses, whereas the curie (Ci) is a unit of radioactivity rather than dose. The sievert (Sv) is another unit of dose equivalent that is part of the International System of Units, which is often used in international contexts, but for dose levels greater than 10 rem in specific settings, the rad is the appropriate and commonly understood unit within the field.