Millisieverts (mSv) = 1 sievert (Sv) Students will not be required to…

The idea

You will never be asked to name the unit of radiation dose from memory, but you will be given doses in sieverts or millisieverts and expected to use them. The conversion is the ordinary milli prefix: 1000 mSv = 1 Sv, so to go from mSv to Sv divide by 1000, and to go the other way multiply by 1000. A dose of 6 mSv is 0.006 Sv, and a dose of 0.05 Sv is 50 mSv. Most exam data appear in millisieverts because everyday doses are small, so always convert both figures to the same unit before you compare or divide them. The same prefix logic you already use for millimetres and milliamps applies here unchanged.

What earns the marks

• A correct conversion between mSv and Sv using the factor of 1000.
• Expressing two given doses in the same unit before comparing them.
• A correct ratio or difference calculated from the converted values.
• The answer written with the unit the question asked for.

Common mistakes and how to put them right

• Multiplying when you should divide, so turning 5 mSv into 5000 Sv.

• Comparing a dose in mSv directly with a dose in Sv.

• Using a factor of 100 or of a million instead of 1000 for the milli prefix.

• Giving a bare number with no unit at the end of a dose calculation.

Exam tips

• Convert both values to millisieverts first, since the numbers are usually easier to handle that way.
• Say in your working which unit you have converted to, so the examiner can follow the comparison.
• You are not expected to recall the unit, so spend no time worrying about its name.