What are rems?

The Rem used to be used in Health Physics to measure radiation dose, it is an acronym for Rontgen Equivalent Man.(The methodology allows for the different effects of different types of radiation). The unit now used is the Sievert (Sv), 1 Sievert = 100 Rem. This is a large unit, so millisieverts are used for practical personnel radiation measures, so 1 millisievert = 100 millirem.

Recommended radiation levels for nuclear workers are set by the ICRP (International Committee for Radiation Protection). These used to be set at 5 Rem/year (50 milliSv) but now the level is 20 milliSv/year ie 2 Rem/year. The use of Rem and millirem has been discontinued in the nuclear industry in favour of Sieverts and millisieverts.

However as someone with nuclear experience going back to 1958 I find it difficult to think in Sieverts. For example I know that 500 Rem will kill roughly 1/2 the people exposed to it within a month, now I have to change that to 5 Sieverts. Fortunately that level of exposure has only happened once (at Chernobyl).