Unit Conversion
The rem and millirem are CGS units in widest use among the American public, industry, and government. SI units are the norm outside of the US, and they are increasingly encountered within the US in academic, scientific, and engineering environments. The SI unit of dose equivalent is the sievert (Sv); conversion is straightforward, as 1 Sv = 100 rem by definition:
| 100.0000 rem | = | 100000.0 mrem | = | 1 Sv | = | 1.000000 Sv | = | 1000.000 mSv | = | 1000000 µSv |
|---|---|---|---|---|---|---|---|---|---|---|
| 1.0000 rem | = | 1000.0 mrem | = | 1 rem | = | 0.010000 Sv | = | 10.000 mSv | = | 10000 µSv |
| 0.1000 rem | = | 100.0 mrem | = | 1 mSv | = | 0.001000 Sv | = | 1.000 mSv | = | 1000 µSv |
| 0.0010 rem | = | 1.0 mrem | = | 1 mrem | = | 0.000010 Sv | = | 0.010 mSv | = | 10 µSv |
| 0.0001 rem | = | 0.1 mrem | = | 1 µSv | = | 0.000001 Sv | = | 0.001 mSv | = | 1 µSv |
The conventional units for dose rate is mrem/h. Regulatory limits and chronic doses are often given in units of mrem/yr or rem/yr, where they are understood to represent an average over the entire year. In many occupational scenarios, the hourly dose rate might fluctuate to levels thousands of times higher for a brief period of time, without infringing on the annual limits. There is no exact conversion from hours to years because of leap years, but approximate conversions are:
- 1 mrem/h = 8766 mrem/yr
- 0.1141 mrem/h = 1000 mrem/yr
The ICRP once adopted fixed conversion for occupational exposure, although these have not appeared in recent documents:
- 8 h = 1 day
- 40 h = 1 week
- 50 week = 1 yr
Therefore, for occupation exposures of that time period,
- 1 mrem/h = 2000 mrem/yr
- 0.5 mrem/h = 1000 mrem/yr
The U.S. National Institute of Standards and Technology (NIST) strongly discourages Americans from expressing doses in rem, in favor of recommending the SI unit. The NIST recommends defining the rem in relation to the SI in every document where this unit is used. For US industries and US firms that do not require the sole use of SI, however, the unit rem is often preferred.
Read more about this topic: Mrem
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